Anthony Peter Schwartz, Robert Reay, Richard Markell INTRODUCTION vari
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Application Note August 1996 Using LTC1325 Battery Management
Anthony Peter Schwartz, Robert Reay, Richard Markell INTRODUCTION variety reasons, desirable charge batteries rapidly possible. same time, overcharging must limited prolong battery life. Such limitation overcharging depends factors such choice charge termination technique multi-rate/ multi-stage charging schemes. majority battery charger available today lock user into fixed charging regimen, with best limited number customization options suit variety application needs battery types. LTC1325 addresses these shortcomings providing user with functional blocks needed implement simple highly flexible battery charger (see Figure which only addresses issue charging batteries also those battery conditioning capacity monitoring. microprocessor interacts with LTC1325 through serial interface control operation functional blocks, allowing software expand scope flexibility charger circuit. This Application Note written with following objectives mind Provide users with insight into architecture operation LTC1325. Outline basic techniques charging various battery types. Present variety useful, tried tested charging circuits. Give overview most common battery types their characteristics. Clarify specialized application-specific terminology. Definitions provided text, well Appendix
IRF9531 (e.g. 8051) p1.4
RTRK NOTE
10µF TANT
DOUT
PGATE 7.5k COILTRONICS CTX100-1-52 7.5k 100µH (NOTE 1N5818
LTC1325 p1.3 p1.2 VBAT TBAT TAMB SENSE FILTER
CREG 4.7µF TANT
THERM NOTE
THERM VBAT CELLS NOTE 500mA RATE
RDIS IRF510 RSENSE
AN64
500pF
3.3µF (NOTE
NOTE THERMISTORS PANASONIC ERT-D2FHL103S THERMISTORS EQUIVALENT. NOTE VREF 160mV, RSENSE CHARGE RATE (160mA). NOTE CHOOSE C/20 TRICKLE CHARGE RATE. NOTE 2.0k 47µF COMPATIBILITY WITH LITHIUM-ION LEAD-ACID
Figure Complete LTC1325 Battery Management System
AN64-1
Application Note
LTC1325 PRIMER main features LTC1325 summarized follows: functional blocks needed build charger: 10-bit Analog-to-Digital Converter (ADC), fault detection circuitry, switching regulator controller with MOSFET driver, programmable timer, precision 3.072V regulator powering external temperature sensors, programmable battery voltage divider. functional blocks placed under control external microprocessor ready adaptability different charging algorithms, battery chemistries, charge rates. Communication with microprocessor simple serial interface, configurable 3-wire 4-wire operation. autonomous fault detection circuitry protect battery against temperature voltage extremes. addition charging, part discharge batteries battery conditioning purposes. includes on-chip circuitry accurate battery capacity monitor (Gas Gauge). charges batteries using switching buck regulator highest efficiency lowest power dissipation. wide supply voltage range (VDD) 4.5V allows battery charger powered from charging supply while charging batteries cells series. charge batteries which require charging voltages greater than VDD. charge batteries from charging supplies greater than VDD. shutdown mode drops supply current 30µA. Charging Circuit Unlike most other charger which employ linear regulator, LTC1325 charges batteries using switching buck regulator. This approach simultaneously maximizes efficiency minimizes power dissipation. only external power components needed inductor, P-channel MOSFET switch, sense resistor catch diode (see Figure internal, programmable battery voltage divider which accommodates cells removes need external resistive divider (for batteries with voltages below maximum 16V). circuits needed controlling loop integrated on-chip external required. LTC1325 operates from 4.5V that powered directly from charging supply. wide supply range makes possible charge cells without need external regulator drop charging supply down supply range LTC1325. These features make LTC1325 easy use. When charging completed charging supply removed, chip does load down other system supplies. LTC1325 powered from system supply, microprocessor program into shutdown mode which quiescent current drops 30µA. shutdown mode digital inputs stay alive await wake-up signal from microprocessor. buck regulator control circuit maintains average voltage across sense resistor (RSENSE) VDAC (see Figure addition, programmable duty cycle modulate P-channel MOSFET driver output (PGATE) reduce average charging current. average charging current given ICHRG VDAC (duty cycle)/Rsense microprocessor VDAC four values, duty cycle five values, giving possible ICHRG values with single RSENSE resistor.
AN64-2
Application Note
CHARGE
PGATE
IRF9531 RTRK
DUTY RATIO GENERATOR DISCHARGE
CSPLY 10µF
111kHz OSCILLATOR
1N5818
SHOT
500k 16pF 125k
BATTERY SENSE 500pF RSENSE FILTER
RDIS NOTE
Figure LTC1325 Charge, Discharge Gauge Circuit
Charge Termination Virtually known charge termination technique implemented with LTC1325. most common these based battery temperature (TBAT), cell voltage (VCELL), time (t), ambient temperature (TAMB), combination these parameters. Unlike other fast charging ICs, LTC1325 does lock user into particular termination technique shortcomings that technique. Instead, provides microprocessor means measure TBAT, TAMB VCELL. keeping track elapsed time, microprocessor means calculate existing termination techniques (including dTBAT/ d2VBAT/dt2), perform averaging reduce probability false termination. This flexibility also means that single circuit charge Nickel-Cadmium, NickelMetal Hydride, Sealed Lead-Acid, Lithium-Ion batteries. LTC1325 on-chip 10-bit successive approximation with 5-channel input multiplexer. Three channels dedicated TBAT, VCELL Gauge (see section Capacity Monitoring); other channels used other purposes such sensing TAMB another external sensor. LTC1325 programmed into Idle mode which charge loop turned off. This permits measurements made without switching noise that present across battery during charging.
VDAC
AN64
3.072V
VR0, GAUGE (GG)
CHIP BOUNDARY
AN64-3
Application Note
Fault Protection LTC1325 monitors battery temperature, cell voltage elapsed time faults prevents initiation continuation charging should fault arise. fault detection circuit (see Figure consists comparators which monitor TBAT VCELL detect temperature faults (LTF), high temperature faults (HTF), cell voltages (BATR, EDV) high cell voltages (MCV). LTF, thresholds external resistor divider maximize flexibility. LTC1325 also includes timer that permits microprocessor charging time before timer fault occurs eight values: 160, minutes time-out. Selecting time-out" disables timer faults (the time-out period effect infinity).
1.6V
Battery Conditioning Under some operating storage conditions, certain battery types (most notably NiCd) lose their full capacity. often necessary subject such batteries deep discharge charge cycles restore lost capacity. LTC1325 programmed into Discharge mode which automatically discharges each cell 0.9V. This voltage defined End-of-Discharge Voltage (EDV). Fault protection remains active Discharge mode protect battery against temperature extremes (LTF, HTF) detect discharge termination point.
3.072V LINEAR REGULATOR RTRK
BATP
BATTERY DIVIDER
VBAT
SENSE
900mV
BATR
100mV
TBAT
Figure LTC1325 Fault Detection Circuitry
AN64-4
AN64
Application Note
Capacity Monitoring LTC1325 programmed into Gauge mode Figure this mode, sense resistor used sense battery load current. battery load connected between VBAT ground that load current passes through sense resistor, producing negative voltage Sense pin. Sense voltage filtered lowpass filter multiplied gain amplifier output converted whenever gauge channel selected microprocessor. accumulating gauge measurements over time, microprocessor determine much charge left battery what capacity remains. APPLICATIONS CIRCUITS Charging Nickel Cadmium Nickel Metal Hydride Batteries desirable charge batteries fully rapidly possible. same time necessary limit overcharging, which adversely affect battery life. meet these requirements, multi-stage charging algorithms recommended NiCd NiMH batteries. Multi-stage charging algorithms consist stages: 2-Stage: 3-Stage: Fast Charge Trickle Charge Fast Charge Top-Off Charge Trickle Charge discharge maintain full capacity. Recommendations battery manufacturer determine which algorithm use. general, best limit overcharge primary charge termination technique several secondary techniques redundancy. Regardless algorithm, basic circuit charge NiCd NiMH cells shown Figure Examples Charging Algorithms
2-Stage NiCd Fast Charge Trickle Charge 2-Stage NiCd Fast Charge Trickle Charge 3-Stage NiMH Fast Charge rate, (10°C) primary termination rate, (45°C) primary termination Time-out secondary termination minutes) C/10 rate, termination needed. rate, (15mV) primary termination Time-out secondary termination minutes) C/10 rate, termination needed
Top-Off Charge C/10 until secondary termination minutes (160 min) Trickle Charge 3-Stage NiMH Quick Charge rate, minute min) minute time-out (40°C) secondary termination C/40 rate, termination
Top-Off Charge C/10 rate until VCELL 1.5V Trickle Charge C/40 rate, termination
During Fast Charge, battery charged maximum permitted rate near full capacity. Top-Off battery charged lower rate bring full capacity thus minimizing overcharge. Finally, during Trickle Charge, battery charged rate that just compensates self-
these algorithms realized with circuit Figure Only software perhaps some component values change.
AN64-5
Application Note
Conditioning Batteries When overcharged extended periods time, some NiCd batteries exhibit what commonly called "memory effect," voltage cell drops 150mV which lead user conclude that battery discharge curve. This condition reversed deeply discharging recharging battery. LTC1325 programmed discharge battery until cell voltage falls below 0.9V (EDV). shown Figure external N-channel MOSFET turned discharge battery. RDIS selected such that discharge current, VBAT/RDIS, within allowable limits battery manufacturer. Discharge currents large with high capacity batteries. power rating RDIS should greater than IDIS2 RDIS. source terminated RSENSE Figure ground. former preferred since VBAT monitors battery voltage battery voltage plus drop across RSENSE. desired possible adjust voltage internal battery divider setting outlined next section. Using End-of-Discharge Voltage Fail-Safe LTC1325, when commanded will discharge battery until cell voltage goes below 900mV nominal, which point fail-safe occurs taken stop discharge. This function most commonly used protection conditioning NiCd NiMH batteries, also used condition Lead-Acid battery reset Guage known point (remaining battery capacity equals zero) battery type. Immediately following discharge, voltage cell NiCd NiMH batteries will typically "rebound" 100mV 200mV. controlling software will need take this rebound into account prevent possible oscillation which would read, fail-safe bits reset, battery discharged more seconds before again indicating stopping discharge. desired, battery divider programmed divide factor that less than number cells battery. example, divider programmed divide-by-5 when number cells battery six, fault occurs 0.9)/6 0.75V. Similarly, programming divider divide-by-6 with three-cell Lead-Acid battery would give 0.9)/3 1.8V cell termination discharge. Operating from Charging Power Supplies Above LTC1325 maximum range 16V. operate from higher supply voltage, necessary things: regulator drop higher supply (VDC) down supply range LTC1325 level shifter between PGATE gate external P-channel MOSFET. level shifter ensures that P-channel MOSFET switched completely. Figure shows cost circuit that will charge cells from supply 160mA. charge current, RSENSE should changed 15µH 0.08 respectively. VDAC 160mV both cases best accuracy. number cells that charged affected series resistance charge path. high charging currents resistance inter-cell connections such solder tabs recommended. zener diode used drop down serve supply LTC1325. should greater than 220. Alternatively, 3-terminal regulator (such LT®1086-12 LT1085-12) replace regulator output voltage (VDD) fixes number cells that charged with circuit about VDD/VEC where maximum cell voltage expected. When battery removed, RTRK pulls VBAT towards VDC. acts clamp prevent VBAT from rising above supply voltage. form simple level shifter. During charging, clamps voltage gate between 0.7V, where reverse breakdown voltage selected limit within maximum rating. logic-level P-channel MOSFETs with maximum ±8V, 3.9V zener such 1N4730A. standard MOSFETs (±20V rating), 1N4740A zener used. When power (VDC) first applied, takes finite time charge that voltage PGATE initially turned breaks down, charging quickly zener drop below VDC. Then PGATE rises, forward
AN64-6
Application Note
1/2W 1N4745A
1N4740A
100k IRF9531
(e.g. 8051) p1.4 DOUT PGATE 7.5k
0.1µF 100µH COILTRONICS CTX100-1-52
1N5818
RTRK C/20 TRICKLE
LTC1325 p1.3 p1.2 VBAT TBAT TAMB SENSE FILTER
1N5818
7.5k
CSPLY 10µF
CREG 4.7µF
THERM NOTE
3.3µF
THERM NOTE
VBAT CELLS 500mA RATE
1N4745A
500pF
RSENSE
AN64
NOTE THERMISTORS PANASONIC ERT-D2FHL103S THERMISTORS EQUIVALENT.
Figure Charging from Supply
biases gate rises diode drop above shuts off. serves hold supply should away some reason. this situation, takes several milliseconds shut completely which means that RSENSE must able withstand brief current pulse (VDC VBAT)/R, where total RDS(ON) RSENSE inductor winding resistance. Diode prevents battery discharge supply removed. Charging "Tall" Batteries cells) charge more than cells, charging supply (VDC) must greater than (assuming cell charge). Since above 16V, regulator level shifter required, explained previous application. Figure shows circuit that will charge batteries with more than cells series. addition, external battery divider added limit voltage seen VBAT below VDD. values selected such that R10/(R8 R10) number cells
battery. battery divider LTC1325 programmed divide one. VDAC programmed 160mV that charging current 160mV/RSENSE 160mA. This charges cell 500mA stack rate. RTRK selected trickle charge battery C/20. same circuit will charge batteries RSENSE changed 15µH 0.08 respectively. Without R14, Figure BATP status flag will always high regardless whether battery present not. therefore possible start charge loop when battery present. current through charge loop will (typically milliampere range). this undesirable, R14, added ensure proper operation BATP flag. selected such that R12/(R11+R12) number cells battery. compares cell voltage against threshold R14. When battery absent, trips turn which then pulls VBAT VDD. This causes BATP flag indicate absence battery.
AN64-7
Application Note
1N4745A
1N4740A
100k IRF9531
(e.g. 8051) p1.4
0.1µF
1N5818
RTRK 1/4W C/20 TRICKLE
DOUT
PGATE 7.5k BS250 7.5k COILTRONICS CTX100-1-52 100µH 1N5818
LTC1325 p1.3 p1.2 VBAT TBAT TAMB SENSE FILTER
CREG 4.7µF
THERM NOTE
5.1k
LT1006
11.3k VBAT CELLS 500mA RATE 78.7k
THERM NOTE
CSPLY 10µF
500pF
3.3µF
RSENSE
AN64
NOTE PANASONIC ERT-D2FHL103S THERMISTORS EQUIVALENT.
Figure Charging More Than Cells
Hardwired Charge Termination Using Thermistors Termination Using Positive Temperature Coefficient (PTC) Thermistors: resistance thermistor increases sharply when temperature rises above specified setpoint (TS). This rapid change exploited implement hardwired charge termination. Figure fixed resistor connected from TBAT input, thermistor connected between TBAT input Sense. Hence controlling element temperature-dependent voltage divider. mounted battery sense temperature. selected such that when battery temperature below divider output voltage between voltages pins. When battery temperature rises above rapid increase resistance device causes divider output
(i.e. voltage TBAT pin) rise above voltage pin. LTC1325 detects temperature fail-safe (LTF stops charging taking PGATE VDD. typical value 45°C. RTHERM1 have typical tolerances ±5°C ±40% respectively. shown Figure 50°C ±5°C, charging will terminate when battery temperature reaches value between 45°C 55°C. series resistance thermistor should range minimize loading LTC1325. principle, possible implement hardwired termination replacing with another with resistance temperature characteristic that matches that shown Figure both PTCs match closely, divider output will respond difference between
AN64-8
Application Note
battery ambient temperature. practice, matched PTCs generally available standard items from thermistor manufacturers therefore recommended such use. hardware termination desired, standard NTCs such those matched over specified temperature range used. With NTCs, divider output will drop battery heats when voltage drops below voltage pin, LTC1325 will detect temperature fail-safe (HTF terminate charging.
(e.g. 8051) p1.4 p1.3 p1.2 DOUT PGATE
RTRK
LTC1325 VBAT TBAT TAMB SENSE FILTER
3.3µF THERM VBAT CELLS
CSPLY 10µF
CREG 4.7µF
500pF
RSENSE
AN64
Figure Hardwired Termination
(e.g. 8051) p1.4 p1.3 p1.2 DOUT PGATE THERM
RTRK
LTC1325 VBAT TBAT TAMB SENSE FILTER
3.3µF THERM VBAT CELLS
CSPLY 10µF
CREG 4.7µF
500pF
RSENSE
AN64
Figure Hardwired Termination
AN64-9
Application Note
Termination Using Negative Temperature Coefficient (NTC) Thermistor: common thermistor battery pack terminated negative terminal battery. During charging, Sense will exhibit switching waveform with peaks 200mV 300mV when VDAC programmed 160mV. This waveform appears TBAT when thermistor terminated negative terminal battery. thermistor slope typically 30mV/°C, switching noise cause premature fail-safes when battery temperature within 10°C trip points. filter (with time constant much greater than clock period 10µs) inserted between TBAT output battery thermistor circuit prevent false fail-safes. Disabling Fail-Safes LTC1325's built-in battery voltage temperature fail-safes easily disabled shown Figure disable temperature fail-safes, TBAT tied resistor LTC1325 made think that battery temperature constant within limits pins. Similarly, VBAT tied same point disable battery voltage fail-safes (MCV, EDV, BATR). LTC1325 battery divider programmed divide-by-1. Battery temperature cell voltage still measured using TAMB channels ADC. external divider (R7, replaces internal divider connected VBAT channel. Gated P-Channel MOSFET Controller When external current-limited voltage source available, charging currents enough that efficiency heat dissipation major concerns, LTC1325 used turn P-channel MOSFET gate current into battery. This circuit makes inexpensive effective combination. battery's current limit during charging current limit charging power supply maximum available current should therefore exceed permissible charge rate battery. With LTC1325 VDAC programmed 160mV setting, voltage Sense below this value, LTC1325 will hold MOSFET until charge
(e.g. 8051) p1.4
DOUT
PGATE 100µH COILTRONICS CTX100-1-52 7.5k THERM NOTE
IRF9531
RTRK NOTE
LTC1325 p1.3 p1.2 p1.5 4.99k VBAT TBAT TAMB SENSE FILTER 30.1k VN2222LL 500pF
1N5818
CREG 4.7µF
CSPLY 10µF
VBAT 500mA
4.99k
RSENSE
AN64
NOTE PANASONIC ERT-D2FHL103S THERMISTOR EQUIVALENT. NOTE CHOOSE C/20 TRICKLE CHARGE RATE.
Figure Charger with TBAT VBAT Fail-Safes Disabled
AN64-10
Application Note
(e.g. 8051) p1.4
IRF9531 DOUT PGATE 7.5k RTRK NOTE
LTC1325 p1.3 p1.2 VBAT TBAT TAMB SENSE FILTER THERM NOTE VBAT CELLS 500mA
CREG 4.7µF
RSENSE
NOTE PANASONIC ERT-D2FHL103S THERMISTOR EQUIVALENT. NOTE CHOOSE C/20 TRICKLE CHARGE.
AN64
Figure LTC1325 Charger Using External Constant-Current Supply
terminated microprocessor, fail-safe occurs. shown Figure inductor catch diode that normally connected positive terminal battery required, switching action occurs drain MOSFET With wall adapter connected, current into battery will always (IADAPTER IEQUIPMENT). additional operational amplifier, such LT1077, allows monitoring this charging current integrating voltage across RSENSE during charging interval. result this integration then measured using LTC1325's auxiliary input VIN. Combined with built-in gauge function during discharge interval (via Sense input), state charge battery reliably determined time. battery pack heavily depleted damaged, wall adapter still used operate equipment putting LTC1325 into Idle mode. Under these conditions battery will receive charging current (except through trickle charging resistor, provided). gauge needed, RSENSE removed Sense should returned ground.
Constant-Potential Charging (Lead-Acid Lithium-Ion) Constant-current charging, which technique choice NiCd NiMH batteries, recommended most Lead-Acid Lithium-Ion applications. Instead, constant-voltage charging regimen required, usually with means limiting initial charging current. Such charging technique generally referred "Constant-Potential" (CP) regimen. LTC1325 first glance constant-current part. Such view capabilities, however, limited. power control section more completely described constant-average-current with both hardware software feedback. hardware loop used current sensing Sense input; software loop, which used control effective output voltage LTC1325 charger circuit, microprocessor control routine conjunction with DAC. Given suitable output filter (the output inductor battery itself), current from section made produce current-limited constant voltage battery's terminals. circuit intended such operation shown Figure
AN64-11
Application Note
(e.g.,80C51) P1.4 P1.3 P1.2 P1.5 DATA CHIP SELECT CLOCK SHDN RMCV1 RTF1 DOUT 7.5k 7.5k IRF9Z30 RTRK 62µHY 1N5818
CREG 4.7µF RMCV2 RTF2
PGATE LTC1325 VBAT TBAT TAMB SENSE FILTER
THERM NOTE
RDIS
CSPLY 10µF
THERM NOTE
2N7002
IRF510 RSENSE 47µF
RTF3
500pF
470k
AN64
NOTE PANASONIC TYPE ERT-D2FHL103S THERMISTOR EQUIVALENT
Figure Constant Potential Battery Management System
Batteries that require charging algorithm generally need rather accurate charging voltage, especially fastcharge applications. this reason LTC1325's internal battery divider often cannot used control charging voltage, tolerance division ratios other than 1:1. does, however, remain useful and/or FEDV detection. measuring battery voltage external resistive divider feeding recommended. external divider resistors should chosen such that voltage will come close possible ADC'c full-scale input voltage without exceeding that value; 3.000V maximum good choice. Using near-full-scale input improves measurement accuracy. further improve charging voltage accuracy, it's good idea ±0.1% ±0.25% tolerance resistors battery voltage divider. Under such conditions, voltage loop error ideally only reference error (±0.8%), plus that bits 1024, ±0.4%) battery divider (±0.1% ±0.25%), total ±1.3% ±1.5% error. "Auxiliary Shutdown" static line from microprocessor small-signal MOSFET, which prevents
battery from discharging through voltage divider string when charging. With external divider place, BATP flag will always high except when Auxiliary Shutdown logic battery installed circuit (see "Charging `Tall' Batteries" above). Battery voltage fail-safes will remain operational (assuming that they VBAT input) although possible make simultaneous fail-safes with battery types. RTRK, needed, maintains battery fully charged condition. suitable software algorithm implement quasi-CP charger this: Establish regular repetition interval voltage servo loop. tLOOP values 10ms 20ms give good results. VDAC 160mV highest charge rates best resolution. Using maximum duty cycle [tON /(tON tOFF)], RSENSE chosen 160mV/(0.95 IMAX), where IMAX nominal maximum current allowed through battery. suitable minimum duty cycle 10%; beyond such duty cycle
AN64-12
Application Note
usually better reduce peak current through battery programming VDAC) than reduce duty cycle further. Perform each following tasks once each servo loop interval (tLOOP): Enter Idle mode operation. Read VCELL. Adjust value entered into timer register software timer) down according actual VCELL target VCELL. VCELL low, timer value increased. VCELL high, timer value decreased. maximum Charge time LTC1325 been tLOOP; minimum 10%. Within that range, duty cycle which loop will operate timer 3(c). timer's interval increased (VCELL low), portion each tLOOP during which LTC1325 into Charge mode increased. timer's interval decreased (VCELL high), LTC1325 commanded into Idle mode greater portion each tLOOP. (0.1 tLOOP), switch VDAC next lower value (note that VDAC value 34mV used). Repeat through until average current into battery, duty cycle, drops below chosen limit. timer-based secondary cutoff often recommended chargers. Terminate software loop with MOSFET "off" state, using RTRK required) maintain battery's charge. flow chart showing principals this voltage servo loop given Appendix Figures B3b. Figure shows "ramp-up" from point where charger first turned maximum charging current required Figure shows "taper-down" which simulates necessary charging algorithm. (This algorithm undergoing refinement press time. latest information implementation optimization, please contact LTC.) have greater values Figure than most circuits this Application Note. This because batteries requiring charge tend have significant positive during interval which charging current flowing through them. time constant (RIN CIN) filters resulting 10ms 20ms ripple before presented VBAT pins. only input will used, omitted, placed from ground, value decreased. circuit Figure deliberately been generalized provide flexibility across common battery types. applications requiring support only specific battery types, which need extensive thermal other protection mechanisms, various components modified removed minimize cost board space. Overcurrent Protection Three common scenarios which battery current exceed acceptable levels are: accidental shorting battery terminals, excessive loads inserting battery into charger reverse. Battery charger damage three cases prevented through thermal overcurrent device limit fault currents. Usually, desirable that this device reset itself when fault goes away. Possible choices bimetallic (thermostatic) switches polymer thermistors. high series resistance traditional ceramic thermistors, even unexcited state, make them unsuitable this application. Bimetallic switches operate sensing battery temperature. nature their operation, these switches cycle long fault remains, causing battery associated components (mechanical well electrical) heat cool down repeatedly. Polymer based thermistors such Raychem PolySwitch® also offer very series resistance until "tripped," have advantages faster response freedom from thermal cycling. Polymer PTCs should chosen such that under normal operation, average charging current (VDAC/RSENSE) less than Hold Current rating keep resistance state. Under fault conditions, Fuse Current should exceed Trip Current rating fuse. This will cause fuse's resistance increase dramatically reduce fault current about VBAT/RFUSE(Trip).
PolySwitch registered trademark Raychem Corporation.
AN64-13
Application Note
PolySwitch should ideally placed between cells battery, close physical contact with cells. this trip point device will reduced battery's temperature increases. Such configuration provides substantial protection battery against shorts across terminals from excessive load currents. will also protect battery accidentally inserted into charger reverse. Figure shows fault current path when battery inserted into charger reverse. Potentially damaging currents flow through this path since Sense resistor usually region less. PolySwitch inside battery pack described above), series with Schottky diode, limits fault currents safe levels. following points should noted choosing diode RSENSE. Normal charging currents should equal less than holding current rating PolySwitch. Temperature affects PolySwitch performance. manufacturer's data should consulted derating factors. Initial fault currents will approximately VBAT/RSENSE battery inserted reverse. This should exceed trip current rating PolySwitch. wattage RSENSE should high enough withstand initial fault currents VBAT/RSENSE. surge current rating should exceed initial fault current VBAT/RSENSE. necessary confirm selected diode's applicability with manufacturer part. addition above scenarios, battery current exceed acceptable levels when battery inserted into charger which charging supply (VDC) turned off. supply exhibits impedance path ground when turned off, diode that intrinsic P-channel MOSFET turn form battery discharge path which flows from battery's positive terminal through inductor, MOSFET internal diode, ground lead sense resistor before returning negative terminal battery. This prevented connecting Schottky diode between (diode anode) source P-channel. section "Current Sinking Sources" more details. Current-Sinking Sources some applications, necessary Schottky rectifier between supply source MOSFET This rectifier prevents battery from discharging backwards through MOSFET which could damage RSENSE. required following conditions met:
IRF9531 (e.g., 8051) p1.4 RTRK DOUT p1.3 p1.2 CREG 4.7µF PGATE
LTC1325 VBAT TBAT TAMB SENSE FILTER THERM
CSPLY 10µF
3.3µF
THERM
500pF
RSENSE
FUSE
AN64
Figure Reversed Battery Protection
AN64-14
Application Note
voltage battery being charged exceed that supply. supply sink current when lower voltage than battery being charged. Most switching power supplies, such those used adapter battery charger supplies portable computers, have very small reverse leakage current several milliamperes most. These would generally need additional Schottky rectifier. examples situations where rectifier necessary are: Charging 7.2V greater battery from battery using cigarette lighter socket. Under coldcranking conditions nominal battery drops automobile's wiring will allow starter motor pull current back lighter socket. Bench-top testing. Many power supplies have internal protection circuitry which will sink current from load rather than allow sourcing load, such charged battery, force current indiscriminately into supply's output. Also, supply with crowbar represents possible current-sinking power supply. Figure depicts basic charger circuit shows proper placement Schottky rectifier DIN. CONCLUSION Through ability accept commands from almost microprocessor, LTC1325 takes advantage power flexibility software avoid locking user into given battery type. This almost endless configurability enables battery system designer choose required charge regimen, charge rate charge termination technique(s) virtually task. Possibilities range from robust basic battery charging technique sophisticated multiple-stage charging algorithms, even several different algorithms entirely, executed with same hardware. this wide range battery types application needs accommodated with same circuit. on-board fault detection circuitry provides additional confidence final design acting "watchdog" microprocessor battery pack. design overall charging circuit made simple possible incorporating functional blocks needed minimizing discrete component count. addition charging batteries, LTC1325 provisions condition batteries measure battery capacity. with LTC1325's charging-related functions, these capabilities afforded maximum versatility value being placed almost completely under software control.
(20V SCHOTTKY) IRF9531 (e.g., 8051) p1.4 p1.3 p1.2 RTRK DOUT PGATE
LTC1325 VBAT TBAT
CSPLY 10µF
TAMB SENSE FILTER THERM
CREG 4.7µF
3.3µF
THERM FUSE
500pF
RSENSE
AN64 F012
Figure Protection Against Discharging Through
AN64-15
Application Note
APPENDIX Overview Battery Types, Terminology, Techniques world increasingly relying upon portable electronic equipment, rechargeable battery systems (battery, battery charger ancillary functional blocks) which power that equipment. These battery systems among defining elements product capability, endurance life. spite this, they commonly considered necessary evil; their design testing, black art. truth that commercially viable battery management systems comprised well understood electronic electrochemical components, with well defined performance characteristics. While this Appendix intended comprehensive treatment battery technology, will provide equipment engineer with practical information choice battery types battery management techniques. There three rechargeable battery types commonly used portable devices. These Nickel-Cadmium (NiCd), Nickel-Metal Hydride (NiMH) Sealed Lead-Acid (SLA). Lithium-Ion (Li-Ion) also beginning receive significant attention, primarily very high energy density measured terms volume weight). Table gives quick overview characteristics these battery types:
Table Battery Type Characteristics
BATTERY CHARACTERISTICS Energy Density W-h/kg Energy Density W-h/liter Cell Voltage SEALED LEAD-ACID NiCd NiMH LITHIUMION 4.20 3.60 2.50 Constant Potential Sloping 1000 6%/MO Highest
useful first-approximation view rechargeable battery that container into which energy poured desired, subsequently consumed needed. This analogy generally conjures image water, which would impose restrictions upon rates filling emptying vessel. fact, battery more akin bottle thick syrup, with bottle having narrow mouth wide base. With such bottle, syrup must delivered into bottle controlled rate pressure prevent possible damage delivery system neck bottle), drawn maximum rate determined amount syrup bottle bottle's shape. carry this analogy just little further, true batteries, with hypothetical syrup bottle, that possible almost contents container take long time last percent out. flow rate will vary with amount remaining, meaning that situations where high rate discharge required battery, "contents bottle" available energy will instantaneously available discharging circuit. Battery recharge times generally break down into several groups. most common these "standardcharge," suitable overnight applications (typically requiring hours) "fast-charge" (typically hours less). Between "quick-charge," which many respects akin standard-charge requires useably shorter interval (about five hours). Examples standard-charge applications cordless telephones systems small computers. Quickcharge batteries commonly found devices which will brief significant power drain several times daily, such cellular phones. Laptop computers cordless tools excellent locations fast-charge systems. these other fast-charge uses there high average drain battery, product's value determined large part availability battery power upon demand. LTC1325 forms comprehensive core battery management systems operating these charge rates; that need changed external components microprocessor algorithm used control charge cycle. Only batteries designed rated fast-charge should subjected fast-
Charging Method Dicharge Profile
#Charge/Discharge >500 >500 Cycles* Self-Discharge 3%/MO 15%/MO 20%/MO Internal Resistance Lowest Moderate Discharge Rate** Until rated capacity available upon discharge. capacity rating battery Ampere-Hours.
Constant Potential Mildly Sloping
Constant Current Flat
Constant Current Flat
AN64-16
Application Note
charge regimen. Similarly, only batteries rated quickcharge should subjected quick-charging conditions. might expected, there important differences between charging regimens used four different battery types. There also more similarities than might expected. Each following sections intended stand alone, suggested that battery system designer read four sections order feel where similarities differences between battery families lie. Terms which specific battery user community, which have special meanings this Appendix, defined Glossary Appendix Using Nickel-Cadmium Batteries Nickel-Cadmium batteries, various forms, have been over years. During that time they have evolved from expensive, special purpose devices battery choice most portable equipment. availability inexpensive sealed cells, with ongoing improvements energy density cycle life, have been driving forces this acceptance. LTC1325 adds this ability easily implement fast-charge routines, gauge algorithms and/or switch mode constant current sources, using very little system overhead printed circuit board space. quick run-down pros cons Nickel-Cadmium batteries: "pros": Good energy density, both weight volume, relative competing technologies. Acceptable charging rates range from 0.1C beyond. Most NiCd cells accept continuous overcharge current 0.1C. very flat discharge profile. lowest cell impedance major battery technologies. Well understood documented electrical behavior electrochemistry. Cells batteries available variety sizes from number vendors. Special purpose batteries available with extended operating temperature ranges. "cons": Cadmium commonly considered environmentally hazardous material. Nickel also coming under environmental scrutiny. NiCd cells have significant self-discharge rate (0.5%/ room temperature). Nickel-Cadmium Standard-Charge applications which allow recharge period about hours "overnight" charge standardcharge regimen method choice. reasons this include: Simplest charging algorithm. Least expensive charge termination techniques. Small power supply required provide charging current. Small charging circuit power components. overall charging system power dissipation. standard-charge relatively straightforward implement. "cookbook" form, such charge requires: Charging Current: 0.1C. Required Charging Voltage: 1.60V/cell greater, plus charger overhead. Charging Temperature Range: 45°C. Charging Time: hours. Charge Termination Method: None required. Secondary Charge Termination Methods: None required. Special issues which require further consideration are: wide temperature range charging, wide temperature range discharging accurate gauging temperature extremes. charging current 0.1C, battery hours, will deliver hours 0.1C) 160% standard capacity battery. temperatures between 25°C, resulting overcharge adequate ensure that battery returned 100% standard capacity. Once
AN64-17
Application Note
cells battery reach their actual capacity operating temperature, mild gassing will occur, enough cause venting other cell damage. Since most NiCd batteries will accept continuous 0.1C charge case temperature between 50°C, charge termination usually required. specialized applications, extended temperature range batteries available which charged 70°C. Charging temperatures below also possible charge current "throttled back" battery temperature decreases. charging current under such conditions should linearly decrease from 0.1C zero current 15°C 25°C. wide temperature range applications, battery ambient) temperature sensor conjunction with LTC1325 excellent provide positive control battery charging current versus temperature, thereby extending battery life. charge acceptance NiCd batteries reduced significantly temperatures above 40°C. This effect only marginally mitigated longer charge times, should taken into account gauging done over extended temperature ranges. example, battery that fully recharged 25°C hours will reach only about standard capacity 45°C after hours. Again, damage will done battery, available capacity during subsequent discharge will less than would otherwise expect. correction parameters gauging function LTC1325 will employed, recommended that manufacturer specific battery question consulted. same that charge acceptance reduced temperatures above 25°C, actual capacity reduced when discharging cell temperatures much removed from 25°C. battery temperatures which actual capacity standard capacity approximately 50°C. Again, more specific data, manufacturer battery used should contacted. Specially rated NiCd cells support higher rate relatively uncontrolled overcharge than ubiquitous 0.1C. This allows quick-charge regimen, which typically 0.33C hours. Charging current interval aside, most other details performing quick-charge same standard-charge. often desirable quick-charge regimens timed charge, reducing charger's output current 0.05C trickle-charge after five-hour recharge interval. Checking cell manufacturer's data will provide further information this, well specified charge rate, permissible continuous overcharge rate, information allowable temperature range. Under some conditions, desirable lower charging rate than 0.1C (for instance, reduce charger power requirements). This feasible only within narrow range: NiCd cells have reduced charge acceptance lower charge rates, lengthening required charge time. This, their self-discharge characteristic (approximately 0.5%/day 23°C), combine make anything under 0.05C very slow potentially unreliable charge rate most cell types. Nickel-Cadmium Fast-Charge recent years class applications arisen which hours hours constitute excessive recharge time. Portable computer equipment excellent example this even battery pack laptop "swapped out" external recharge, often needed again within several hours, fully charged ready use. this case, fast-charge techniques which LTC1325 makes practical fast-charge regimen implies: recharge within hour; 100% recharge within three hours. method determining optimum charge termination point(s). Backup charge termination method(s) ensure best battery life. Highly efficient available charging energy. Increased product value through better battery utilization greater customer satisfaction. Unlike standard-charge quick-charge regimens, there best fast-charge Nickel-Cadmium battery. Variables introduced allowable cost size application, continuing evolution Ni-Cd cells accomodate faster charge rates, specific battery vendor(s) chosen will influence final choice charging technique. There several areas
AN64-18
Application Note
industry consensus, however, regarding suitable fastcharging NiCd batteries: Charging Current: 1.0C 2.0C. Required Charging Voltage: 1.80V/cell greater, plus charger overhead. Charging Temperature Range: 10°C 40°C. Charging Time: Three hours (90% charge typically returned within first hour). Suitable Charge Termination Methods: Table Suitable Secondary Charge Termination Methods: Table Special issues which require further consideration are: accurate gauging temperatures over appropriate mechanical integration battery pack into equipment. objective fast-charging NiCd battery crudely stated, cram much energy takes bring battery back fully charged state into that battery short time possible. Since current proportional energy divided time, charging current should high battery system will reasonably allow. Generally, NiCd batteries rated fast-charge designed around maximum charging rate. rate, more than usable discharge capacity battery typically returned within first hour. Higher rate cells exist, they more oriented special applications will discussed here, except note that LTC1325 capable handling charging routines required such cells, should that required. Fast-charging compelling benefits, places certain demands upon battery system. properly performed fast-charge yield cell life many charge/ discharge cycles. high charging rates involved, however, engender correspondingly more rapid electrochemical reactions within cell. Once cell goes into overcharge, these reactions cause rapid increase internal cell pressure, cell's temperature. Figure shows Voltage, Pressure Temperature characteristics Nickel-Cadmium cell being charged rate. seen that, cell approaches 100%
Table Fast-Charge Termination Techniques Nickel-Cadmium Batteries
Voltage Cutoff (VCO) Negative (-V) Zero Uses absolute cell voltage determine cell's state charge. generally recommended NiCd charging regimens. Looks relatively pronounced downward slope cell voltage which NiCd exhibits (30mV 50mV) upon entering overcharge. Very common NiCd applications simplicity reliability. Waits time when voltage cell under charge stops rising, curve" prior downslope seen overcharge. Sometimes preferred over causes less overcharging. Looks increasing slope cell voltage (positive dV/dt) which occurs somewhat before cell reaches 100% returned charge (prior Zero point). longer widely used. NiCd cell approaches full charge, rate voltage rise begins level off. This method looks zero more commonly, slightly negative value second derivative cell voltage with respect time. Uses cell's case temperature (which will undergo rapid rise cell enters high-rate overcharge) determine when terminate high-rate charging. good backup method, susceptible variations ambient temperature conditions make good primary cutoff technique. Uses specified increase NiCd cell's case temperature, relative ambient temperature, determine when terminate high-rate charging. popular, relatively inexpensive reliable cutoff method. Uses rate increase NiCd cell's case temperature determine point which terminate high-rate charge. This technique inexpensive relatively reliable long cell housing have been properly characterized.
Voltage Slope (dV/dt) Inflection Point Cutoff (d2V/dt2, IPCO)
Absolute Temperature Cutoff (TCO)
Incremental Temperature Cutoff (TCO)
Delta Temperature/Delta Time (T/t)
AN64-19
Application Note
1.75 1.50
INTERNAL PRESSURE (PSIG) CELL VOLTAGE
CELL TEMPERATURE (°C)
PRESSURE CHARGE INPUT CAPACITY)
AN64 FA01
CELL VOLTAGE
1.25 1.00 0.75 0.50 0.25
TEMPERATURE
sensing uses thermistors measure case temperature cell, cells battery, while also measuring ambient temperature. 10°C differential between cell ambient typical high-rate termination criterion. single-thermistor variant "classic" approach made possible through combined power LTC1325 microprocessor: cell temperature measured just before commencing charge, assumed ambient temperature. This baseline value then becomes reference against which further temperature measurements compared.) illustration fast-charging NiCd batteries, this document will charge rate, three-stage algorithm. three stages are: Fast-Charge rate, until determined charging system that high-rate portion charge regimen must terminated. this point, charge will typically have returned between battery's actual capacity. Top-Charge 0.1C hours, additional 0.2C battery. This will bring battery back 100% usable capacity. Trickle-Charge between 0.02C 0.1C counter NiCd's self-discharge value about 0.5%/day. Unless battery being used unusual application, there little advantage using trickle-charge rate different from 0.1C top-charge rate, which most NiCd cells tolerate indefinitely. trickle-charge same top-charge rate, charge regimen illustrated effectively only stages. This uncommon NiCd batteries. cannot overstated that high-rate portion fastcharge regimen must terminated once battery being charged reached appropriate cutoff point. Murphy taught prepare unexpected. each method consider: "How this method fail?" give just example each case: contact resistance charging path could mask downslope battery's terminal voltage, causing microprocessor miss termination point. termination, ambient temperature might indicative battery's temperature start charge (e.g., recharging battery just removed from cooler environment warmer one),
Reproduced with permission Butterworth-Heinemann, Rechargeable Batteries Applications Handbook, copyright 1992
Figure NiCd Voltage, Pressure, Temperature Characteristics During Charge (23°C Ambient)
capacity, charging current must reduced terminated. Left unchecked, overcharge rate will ultimately cause cell's safety vent open. This results loss gaseous electrolyte ambient, permanent diminution cell capacity. Similarly, allowing temperature cell rise excessively will cause degradation internal materials, again reducing cell life. science fast-charging largely that determining when battery achieved between 100% dischargeable capacity. that point charging circuit must switch from fast-charge current level level appropriate finish charging and/ maintain charge battery. Some common methods doing this outlined Table Table shows, there number techniques which have been been successfully employed purpose determining when terminate high-rate interval fast-charge regimen. Individual application requirements, manufacturer's recommendations, must course considered carefully before making final design decision. Nonetheless, techniques detecting point which make transition from high-rate charging top-charging have become especially popular over years, used here examples. These methods. approach looks point which cell battery voltage reaches peak during charging, holds this maximum value. high-rate charge then terminated when voltage cell declined value 15mV 30mV.
AN64-20
Application Note
which would keep significant battery-to-ambient temperature differential from appearing. Failure charger system recognize cutoff point, whatever reason, quickly irretrievably damage battery. avoid such damage, inexpensive redundancy solution. With capabilities LTC1325 already hand, best plan simply employ both methods. then reasonable expect that techniques will result successful high-rate charge termination. this example regimen good choice primary high-rate charge termination NiCd batteries would sensing, with serving backup. give Murphy's gremlins harder time there maximum minimum operating temperatures cell voltages which LTC1325 recognize. LTC1325 also timer feature which will turn charge current battery unless timer reset within certain interval. These preset limits serve protect battery from severe overcharge even system's microprocessor should fail altogether. mentioned above, fast-charge current levels cause rapid evolution within NiCd cell. Since recombination inside cell slower reduced temperatures, pressure inside cell will rise cell temperature decreases. This places lower limit permissible fast-charge temperature range. Similarly, cell's charge acceptance decreases elevated temperatures. Hence, although recombination occurs much more rapidly, there danger more being generated than cell mechanisms handle. This places upper boundary fast-charge temperature range. Putting numbers these limits, 10°C 15°C common minimum figures with high 40°C 45°C. Using LTC1325 conjunction with microprocessor ensure that indicated operations occur within manufacturer's rated temperature limits will significantly extend life cell battery. most accurate gauging desirable take into account battery's actual temperature during charge temperature during discharge. Both these have effect upon ratio actual capacity standard capacity. This effect especially pronounced battery charged ambient temperature above 25°C and/or discharged below. specific data with which calibrate gauge function against charge discharge temperatures, manufacturer cells batteries being used should contacted. During fast-charge battery will warm vent unlikely case overstress failure. prudent engineering allow these contingencies mechanical design stage equipment which battery will reside. Again, manufacturer cells battery used should consulted specific guidance. Using Nickel-Metal Hydride Batteries Nickel-Hydrogen couple been known least years, until recently been costly most specialized applications. Recent developments manufacture NiMH cell, specifically hydrogen-bearing negative electrode, brought NiMH technology into realm commercial viability. present NiMH batteries remain somewhat more expensive than either Nickel-Cadmium units. However, applications requiring energy densities which NiMH provides, readily justify higher price. should also noted that NiMH mature enough technology useful reliable, young enough that prices should continue decline performance improve. LTC1325's features flexibility make excellent choice Nickel-Metal Hydride applications, providing ability easily implement modify fast-charge routines, gauge algorithms and/or switch-mode constant current sources, using very little system overhead printed circuit board space. quick rundown pros cons Nickel-Metal Hydride batteries: "pros": Excellent energy density, both weight volume, relative competing technologies. Acceptable charging rates range from 0.1C beyond (fast-charge capability virtually given NiMH). flat discharge profile. Well understood documented electrical behavior electrochemistry.
AN64-21
Application Note
Cells batteries available variety sizes from number vendors. anticipated that cell formulations will eliminate cadmium from NiMH product. "cons": Nickel coming under scrutiny potential ecological hazard. NiMH cells have significant self-discharge rate (0.5%/ 1%/day room temperature). Careful attention overcharge NiMH cells required, even standard-charge rates. NiMH cells command price premium relative NiCd cells present time. MiMH cells presently cover same temperature ranges either NiCd units. Nickel-Metal Hydride Standard-Charge applications which allow recharge period about hours "overnight" charge standardcharge regimen method choice. reasons this include: Simplest charging algorithm. Least expensive charge termination techniques. Small power supply required provide charging current. Small charging circuit power components. overall charging system power dissipation. standard-charge relatively straightforward implement. "cookbook" form, such charge requires: Charging Current: 0.1C, switching 0.025C tricklecharge. Required Charging Voltage: 1.60V/cell greater, plus charger overhead. Charging Temperature Range: 50°C. Charging Time: hours. Charge Termination Method: Timer. Secondary Charge Termination Methods: None required. Special issues which require further consideration are: wide temperature range discharging accurate gauging temperature extremes. charging current 0.1C, battery hours, will deliver hours 0.1C) 160% standard capacity battery. temperatures between 25°C, resulting overcharge adequate ensure that battery returned 100% standard capacity. Once this occurred charging rate must reduced sufficiently that cell venting does occur. same time 1%/day self-discharge NiMH cell needs countered with suitable trickle-charge rate. resulting two-level constant-current charger usually switches 0.025C rate after 0.1C main charge. NiMH battery will show modest temperature increase (typically 9°C) after hours standard-rate charging. However, this value tightly defined rate temperature rise quite gradual charging cycle. This rules thermal charge termination standard-charge regimen. better approach timed-charge technique which applies standard-rate charging current hours then drops back 0.025C trickle-charge. refinement this break main charging interval into numerous shorter intervals under control timer internal LTC1325. this way, even microprocessor controlling battery system should "lock up," permanent damage battery will prevented. Charging temperatures below above 45°C recommended. addition, NiMH batteries should discharged beyond range 20°C 50°C. wide temperature excursion ambient anticipated, thermal sensor conjunction with LTC1325 excellent ensure that battery operations occur only within their permissible temperature boundaries, which will significantly extend battery life. charge acceptance NiMH batteries reduced significantly temperatures above 40°C. This effect should taken into account gauging done over extended temperature ranges. this regard, performance NiMH Nickel-Cadmium batteries quite similar. NiMH battery that will recover 100% standard capacity after hours 25°C will attain only about standard capacity 45°C. Hence battery's available capacity during subsequent discharge will less than
AN64-22
Application Note
would otherwise expect. correction parameters gauging function LTC1325 will employed, recommended that manufacturer specific battery question consulted. same that charge acceptance reduced temperatures above 25°C, actual capacity reduced when discharging cell temperatures much below 25°C. Typical figures actual capacity standard capacity 0°C, 20°C. Again, more specific data manufacturer battery used should contacted. Generally speaking, it's good idea lower charging rate than 0.1C. This part fact that NiMH cells have reduced charge acceptance lower charge rates, lengthening required charge time, part fact that their self-discharge rate approximately 1%/day 23°C increases quickly with temperature. Nickel-Metal Hydride Fast-Charge recent years class applications arisen which hours hours constitute excessive recharge time. NiMH batteries, with their relatively high energy densities, were perfected largely mobile portion this market. Portable computer equipment excellent example NiMH fast-charge application even battery pack laptop "swapped out" external recharge, often needed again within several hours, fully charged ready use. this case techniques which LTC1325 makes practical Such fast-charge implies: recharge within hour; 100% recharge within four hours. method determining optimum charge termination point(s). Backup charge termination method(s) ensure best battery life. Highly efficient available charging energy. Increased product value through better battery utilization greater customer satisfaction. fast-charge battery system involves: Charging Current: 1.0C. Charging Time: Three hours (90% charge typically returned within first hour). Required Charging Voltage: 1.80V/cell greater, plus charger overhead. Charging Temperature Range: 15°C 30°C optimal (consult manufacturer permissible range). Charge Termination Method: Table Secondary Charge Termination Methods: Table Special issues which require further consideration are: accurate gauging temperatures other than 25°C appropriate mechanical integration battery pack into equipment. objective fast-charging NiMH battery crudely stated, cram much energy takes bring battery back fully charged state into that battery short time possible. Since current proportional energy divided time, charging current should high battery system will reasonably allow. Generally, NiMH batteries rated maximum charging rate. that rate, more than useable discharge capacity battery typically returned within first hour. course, LTC1325 will also support charging higher rate cells they become available. Fast-charging compelling benefits, places certain demands upon battery system. properly performed fast-charge yield cell life many charge/ discharge cycles. high charging rates involved, however, engender correspondingly more rapid electrochemical reactions within cell. Once cell goes into overcharge, these reactions cause rapid increase internal cell pressure cell's temperature. Figure shows Voltage Temperature characteristics Nickel-Metal Hydride cell being charged rate. seen that, cell approaches 100% capacity, charging current must reduced terminated. Left unchecked, overcharge rate will ultimately cause cell's safety vent open. This results loss gaseous electrolyte ambient permanent diminution cell capacity. Similarly, allowing temperature cell rise excessively will cause degradation internal materials, again reducing cell life. science fast-charging largely that determining when battery achieved between 100%
AN64-23
Application Note
Table Fast-Charge Termination Techniques Nickel-Metal Hydride Batteries
Voltage Cutoff (VCO) Negative (-V) Zero Uses absolute cell voltage determine cell's state charge. generally recommended NiMH charging regimens. Looks downward slope cell voltage which NiMH exhibits 15mV) upon entering overcharge. Common NiMH applications simplicity reliability. Waits time when voltage cell under charge stops rising, curve" prior downslope seen overcharge. Sometimes preferred over causes less overcharging, easier detect reliably (due small NiMH cell). Common NiMH applications. Looks increasing slope cell voltage (positive dV/dt) which occurs somewhat before cell reaches 100% returned charge (prior Zero point). widely used. NiMH cell approaches full charge, rate voltage rise begins level off. This method looks zero more commonly, slightly negative value second derivative cell voltage with respect time. Uses cell's case temperature (which will undergo rapid rise cell enters high-rate overcharge) determine when terminate high-rate charging. good backup method, susceptible variations ambient temperature conditions make good primary cutoff technique. Uses specified increase NiMH cell's case temperature, relative ambient temperature, determine when terminate high-rate charging. popular, relatively inexpensive reliable cutoff method. Uses rate increase NiMH cell's case temperature determine point which terminate high-rate charge. This technique inexpensive relatively reliable long cell housing have been properly characterized.
Voltage Slope (dV/dt) Inflection Point Cutoff (d2V/dt2, IPCO)
Absolute Temperature Cutoff (TCO)
Incremental Temperature Cutoff (TCO)
Delta Temperature/Delta Time (T/t)
1.60 1.55
1.50 1.45 1.40 1.35 1.30 1.25
VOLTAGE TEMPERATURE
CHARGE INPUT TYPICAL CAPACITY) Data used courtesy Duracell, Inc.
AN64 FA02
Figure NiMH Voltage Temperature Characteristics During Charge (20°C Ambient)
dischargeable capacity. that point charging circuit must switch from fast-charge current level level appropriate finish charging and/or maintain charge battery. Some common methods doing this outlined Table
Table shows there number techniques which have been been successfully employed purpose determining when terminate high-rate interval fast-charge regimen. Individual application requirements, manufacturer's recommendations, must course considered carefully before making final design decision. Several techniques detecting point which make transition from high-rate charging top-charging have gained especially wide acceptance NiMH community. Among these T/t, TCO, d2V/dt2 methods. sensing measures rate change case temperature cell, cell battery with respect time. When this rate rise reaches 1°C/minute, almost dischargeable capacity been returned cell high-rate charge should terminated. sensing measures difference between case temperature cell, cells battery, while also measuring ambient temperature. 15°C differential between cell ambient typical high-rate termination criterion. approach looks point which
BATTERY TEMPERATURE (°C)
AN64-24
BATTERY VOLTAGE (V.p.c.)
Application Note
cell battery voltage peaks during charging, holds this maximum value. high-rate charge then terminated when voltage cell declined value 10mV. d2V/dt2 technique looks slowing rate rise battery's terminal voltage. This trend, properly filtered processed system's software, will yield negative second derivative battery voltage when battery approaches complete recharge. important note that under certain conditions, particularly following intervals storage, NiMH battery give erroneous voltage peak charging commences. this reason, reliable fast-charge cycle should deliberately disable voltage-based sensing technique first five minutes charging interval. illustration fast-charging NiMH batteries, this document will regimen recommended Duracell, Inc. three stages this regimen are: Fast-charge rate, until determined charging system that high-rate portion charging cycle must terminated. this point, charge will typically have returned between battery's actual capacity. Top-charge 0.1C hour additional 0.1C battery. This will bring battery back 100% usable capacity. Trickle-charge 0.0033C counter self-discharge characteristic Nickel-Metal Hydride, while exposing battery excessive overcharge. Nickel-Metal Hydride batteries suffer quickly severely from protracted overcharge. prevent damage battery manufacturer's algorithms recommend trickle-charge value. shown, Duracell recommends 0.0033C while many other vendors specify 0.025C. exact value this trickle-charge, well specific overall charging regimen, application vendor dependent, literature selected battery supplier should consulted. cannot overstated that high-rate portion fastcharge regimen must terminated once battery being charged reached appropriate cutoff point. Murphy taught prepare unexpected. each method consider: "How this method fail?" illustrate example: contact resistance charging path could mask downslope battery's terminal voltage, causing microprocessor miss termination point. case termination, ambient temperature might artificially prevent rapid enough change temperature from occuring (e.g., recharging battery while sits airstream conditioner). Failure charger system recognize cutoff point, whatever reason, quickly irretrievably damage battery. avoid such damage, inexpensive redundancy solution. With capabilities LTC1325 already hand, best plan simply employ more methods. then reasonable expect that techniques will result successful high-rate charge termination. Duracell's suggested regimen primary technique terminating high-rate charge sensing, with serving backup. give Murphy's gremlins harder time there maximum minimum operating temperatures cell voltages which LTC1325 recognize. example, Duracell recommends using third, TCO-based "safety" shut high-rate charge down battery temperature ever exceeds 60°C absolute. LTC1325 also timer feature which will turn charge current battery unless timer reset within certain interval. only does this provide extra margin safety, simplify charging well: Duracell's regimen calls hour timer-controlled 0.1C overcharge. LTC1325 offload this timing from system processor. Hence, battery charging task simplified battery protected from severe overcharge even system's microprocessor should fail altogether. mentioned above, fast-charge current levels cause rapid evolution within NiMH cell. Since recombination inside cell slower reduced temperatures, pressure inside cell will rise cell temperature decreases. This places lower limit permissible fast-charge temperature range. Similarly, cell's charge acceptance decreases elevated temperatures. Hence, although recombination occurs much more rapidly, there danger more being generated than cell mechanisms handle. This places upper boundary fast-charge temperature range. Putting numbers these limits, 10°C 15°C common minimum
AN64-25
Application Note
figures with high 40°C 45°C. This temperature span constitutes limit fast-charging NiMH batteries; they will give longer life better performance charged between 15°C 30°C. Using LTC1325's measurement capabilities ensure that indicated operations occur within manufacturer's rated temperature limits will significantly extend life cell battery. most accurate gauging, desirable take into account battery's actual temperature during charge temperature during discharge. Both these have effect upon ratio actual capacity standard capacity. This effect especially pronounced battery charged ambient temperature above 25°C and/or discharged below. specific data with which calibrate gauge function against charge discharge temperatures, manufacturer cells batteries being used should contacted. During fast-charge battery will warm vent unlikely case overstress failure. prudent engineering allow these contingencies mechanical design stage equipment which battery will reside. Again, manufacturer cells battery used should consulted specific guidance. Using Sealed Lead-Acid Batteries Lead-Acid batteries "venerable elders" among rechargeable power sources. They have been known various forms substantially over century. does imply weakness many most significant developments Lead-Acid cells, including those which have made portable Sealed Lead-Acid (SLA) construction practical, have taken place last years less. Concerns about safety stability sulfuric-acid electrolyte system have been addressed, first wellknown "Gel Cell," thereafter modern "starvedelectrolyte" technologies. Improvements purity materials, optimization internal cell structure portable battery applications opposed traditional automotive market which imposes unique demands) have made battery serious contender many applications. smaller ratings batteries compare favorably cost Watt-Hour with NiCd batteries superior NiMH devices; higher Watt-Hour ratings technology usually clear choice. With minimum board space system overhead, LTC1325 provides programmable switchmode charging controller. also carries on-chip necessary battery monitoring safeguard circuitry, means readily implement gauge algorithms. quick rundown pros cons Sealed Lead-Acid batteries: "pros": electrochemistry electrical behavior batteries very well understood documented moderate charge rates broad range discharge rates. technology lends itself prismatic batteries well cylindrical cells. batteries available with wider operating temperature ranges than either NiCd NiMH batteries. Excellent cost/Watt-Hour, especially larger size cells batteries. Very self-discharge rates: 0.2%/day 25°C cell impedance with good capability handle high pulse currents. cells available variety sizes from number vendors. "cons": cell lowest energy density, weight volume, three technologies. batteries deliver their best performance under constant voltage pseudo-constant voltage) charge regime. Lead commonly considered environmentally hazardous material. cells susceptible damage from overcharge, repeated deep discharge, and/or cell reversal. discharge profile cell flat that NiCd cell, that NiMH cell most applications.
AN64-26
Application Note
Sealed Lead-Acid Standard-Charge applications which allow recharge period hours more period from extended "overnight" charge "float charge"-- standard-charge regimen choice. reasons this include: charge termination required. Frequently requires temperature compensation. Small power supply required provide charging current. Small charging circuit power components. overall charging system power dissipation. Excellent battery life charging stress. standard-charge relatively straightforward implement. "cookbook" form, such charge requires: Charging Current: Limited 0.25C less. Charging Voltage: 2.25V/cell 2.30V/cell, plus charger overhead. Charging Temperature Range: 40°C. Charging Time: hours longer. Charge Termination Method: None required. Secondary Charge Termination Methods: None required. Special issues which require further consideration are: wide temperature range charging, wide temperature range discharging, accurate gauging under varying conditions use. Sealed Lead-Acid (SLA) batteries generally charged using constant voltage source with deliberately imposed current limit (essentially current-limited voltage regulator), charger which will, terms electrochemical effects seen battery, were such source. charging regimen which this gives rise known "Constant Voltage," more commonly, "Constant Potential." purposes this document term "Constant Potential" (CP) will used. reasons using charge regimen various, three principal ones these: Charge acceptance (the efficiency conversion previously removed electrical energy back into chemical potential) reduced charging current through cell increased. Once full charge achieved, continued charging current through cell will have irreversible oxidizing effect upon positive plate battery, ultimately reducing battery capacity. Most importantly from standpoint designing practical charger, there reliable know cell's state charge based upon terminal voltage temperature. significantly discharged cell undergoing charging will initially attempt draw very high currents, cells impedance devices. function current-limiting regimen keep peak current flowing into cell within cell's (and charger's) ratings. Following current-limited phase charging profile, charging technique combination with characteristics devices cause cell under charge essence regulate charging current. cell vendor's recommendation charging voltage (typically 2.25V/cell 2.30V/cell 20°C) followed, cell's charging current will naturally taper with time cell goes slightly into overcharge. Under these conditions fully discharged cell will essentially cease charging once achieved 110% returned charge which results 100% dischargeable capacity. remaining lost heating other parasitic reactions. This simple charging concept, sometimes combined with compensation ambient temperature 2mV/°C -3mV/°C, depending upon manufacturer), will provide highly satisfactory results over good temperature range. range 40°C typical, with some vendors specifying their products operation temperatures 50°C more. Figure shows which charge current tapers returned capacity rises under such charging regimen. Figure reproduction Figure from body this Application Note, shows LTC1325 used provide necessary functions battery management. body this Application Note, Figures Appendix also relevant here. charge acceptance batteries reduced temperatures below about 0°C, actual capacity reduced when discharging cell temperatures much
AN64-27
Application Note
CURRENT LIMIT CHARGE CURRENT CAPACITY RETURNED STATE CHARGE
gauging function LTC1325 will employed, recommended that manufacturer specific battery question consulted. Under some conditions, desirable lower charging rate than 0.1C (for instance, reduce charger power requirements). This quite feasible with batteries their self-discharge rates. batteries have excellent charge acceptance characteristics lower charge rates. Ultimately, limiting issue usually maximum practical time allowable recharge. During charging, battery warm and/or vent. prudent engineering allow these contingencies mechanical design stage equipment which battery will reside. manufacturer battery used should consulted specific guidance. Sealed Lead-Acid Fast-Charge many cases, hours more will constitute excessive recharge time. Portable instrumentation excellent example even battery pack instrument "swapped out" external recharge, often needed again before out, fully charged
CHARGING CURRENT
TIME
AN64 FA03
Reproduced with permission Butterworth-Heinemann, Rechargeable Batteries Applications Handbook, copyright 1992
Figure Typical Charging Current Capacity Returned Charge Time Charging
lower than 25°C. battery temperature which actual capacity standard capacity approximately 0°C. Similarly, adjustment indicated capacity desired continuous discharge current will rate significantly greater than 0.1C. desirable take these effects into account gauging done over extended temperature ranges. correction parameters
(e.g.,80C51) P1.4 P1.3 P1.2 P1.5
DATA CHIP SELECT CLOCK SHDN DOUT 7.5k 7.5k IRF9Z30 RTRK 62µHY 1N5818
RMCV1
RTF1
CREG 4.7µF RMCV2 RTF2
PGATE LTC1325 VBAT TBAT TAMB SENSE FILTER
THERM NOTE
RDIS
CSPLY 10µF
THERM NOTE
2N7002
IRF510 RSENSE 47µF
RTF3
500pF
470k
AN64 FA04
NOTE PANASONIC TYPE ERT-D2FHL103S THERMISTOR EQUIVALENT
Figure LTC1325 Constant Potential Battery Management System
AN64-28
Application Note
ready use. this case sophisticated fast-charge techniques which LTC1325 makes practical fast-charge regimen implies: Significant recharge within hour; 100% recharge within three hours. Suitable means determine charge termination point. backup charge termination method ensure best battery life. Highly efficient available charging energy. Increased product value through better battery utilization greater customer satisfaction. fast-charge very similar standardcharge. recommended that section standardcharging Sealed Lead-Acid batteries read before reading this section. There only three significant differences between sections: charging voltage increased increase charging current). Temperature compensation definitely required rate 5mV/°C, preferably from sensor mounted near battery case. Fast-charge termination required. Charging Current: Vendor-dependent. vendor used reference suggests 1.5C. Charging Voltage: 2.45V/cell 2.50V/cell, plus charger overhead. Charging Temperature Range: 30°C. Charge Termination Method: Current Cutoff. Charging Time: Three hours; charge typically returned within first hour. Secondary Charge Termination Methods: Timer. Special issues which require further consideration are: wide temperature range charging, wide temperature range discharging, accurate gauging under varying conditions use. primary termination method, "Current Cutoff" (CCO), looks absolute value average charging current flowing into battery. When that current drops below 0.01C battery charged needs only trickle current about 0.002C. backup method should 180-minute time-out, according recommendations vendor suggesting 1.5C high-rate current. During fast-charge battery will warm some venting occur. prudent engineering allow these contingencies mechanical design stage equipment which battery will reside. manufacturer battery used should consulted specific guidance. other regards, techniques fast-charging cells batteries same those used standard-charging these devices. simple circuit, coupled with straightforward software servo loop, provides high performance battery charger gauge well significant built-in fault detection protection mechanisms. Using Lithium-Ion Batteries four battery types discussed this Appendix, Lithium-Ion (Li-Ion) newest. Li-Ion cells offer excellent service life, considered environmentally sound, easily manufactured true prismatic (rectangular) format, most importantly, they have highest energy density, both terms Watt-Hours/kg WattHours/Liter, cells discussed. merely telling associated microcontroller whether NiMH Li-Ion battery present system, LTC1325 using same hardware accommodate either type cell technology. Li-Ion batteries charged using constant voltage source with deliberately imposed current limit (essentially current-limited voltage regulator), charger which will, terms electrochemical effects seen battery, were such source. charging regimen which this gives rise known "Constant Voltage," more commonly, "Constant Potential." purpose this document, term "Constant Potential" (CP) will used. quick run-down pros cons Lithium-Ion batteries: "pros": Superb energy densities, both Watt-Hours/Liter Watt-Hours/kg, relative competing technologies.
AN64-29
Application Note
High average cell voltage during discharge (3.6V). Excellent cycle life characteristics. Very self-discharge rates 0.3%/day 25°C). Environmentally sound (not heavy-metal technology). Li-Ion cells available prismatic (rectangular) form factors. "cons": Susceptible irreversible damage taken into deep discharge. Susceptible loss capacity catastrophic failure overcharged. Efficient cell capacity requires extremely tight control charging voltage. Lithium-Ion Fast-Charging Li-Ion fast-charge conceptually quite simple: Charging Current: Charging Voltage: 4.20V ±0.05V (some cells require slightly different voltages) Charging Temperature Range: 40°C. Charging Time: Hours Hours. Charge Termination Method: timer typical (consult cell manufacturer). Secondary Charge Termination Methods: None required. Special issues which require further consideration are: wide temperature range charging, wide temperature range discharging, accurate gauging under varying conditions use. significantly discharged cell undergoing charging will initially attempt draw very high currents, Li-Ion cells relatively impedance devices. function current-limiting regimen keep peak current flowing into cell within cell's (and charger's) ratings. Following current-limited phase charging profile, charging technique combination with characteristics Li-Ion cell cause cell under charge essence regulate charging current. cell vendor's recommendation charging voltage (usually 4.20V ±50mV 23°C) followed, cell's charging current will naturally taper with time. Figure illustrates such charging behavior. This straightforward charging regimen best knowledge, that required charge cell. Multicell Li-Ion battery packs (e.g., more cells series) incorporate custom circuit monitoring state charge each individual cell within battery. This circuit also provides extensive overcharge other major fault protection. LTC1325 readily charge either single cell, manufacturer's finished battery pack. LTC1325 first glance, constant-current part. Such view capabilities, however, limited. power control section more completely described constantaverage-current PWM, with capability "software" feedback. Given suitable output filter (probably only output inductor battery itself), current from section turned into suitably constant voltage battery's terminals this voltage used charge Li-Ion cells batteries. software feedback loop mentioned previously allows controlling processor handle aspects charging, rather than demanding that important variables hardwired. necessary servo loop created follows: Establish regular repetition interval voltage servo loop. 10ms 20ms gives good results sealed lead-acid Li-Ion cells batteries. VDAC 150mV best resolution. RSENSE then chosen 150mV/(0.9 IMAX), where IMAX maximum current allowed through battery. Perform each following tasks once each servo loop interval: Enter Idle mode operation. Each VCELL. Adjust value entered into timer register software timer) down according actual VCELL target VCELL. VCELL high timer value increased. VCELL timer value decreased.
AN64-30
Application Note
Assume that maximum charger will each servo loop interval. Enter Charge mode operation, period between servo loop interval determined (d)]. essence, timer's period being subtracted from charging time available during each servo loop interval, perform duty cycle modulation processor. 2ms, switch VDAC next lower value. Repeat through until current into battery drops below 0.002C, until three hours charging have elapsed. Terminate software loop with MOSFET (Figure "off" state. trick-charging resistor used. Lithium-Ion System Issues Lithium-Ion cells batteries require tight control over voltages which they exposed. This makes virtually mandatory that precision external resistive divider used scale battery voltage present auxiliary input highest input voltage possible consistent with overloading LTC1325's should used; 3.000V full-scale good choice. This gives best resolution helps preserve accuracy part when measuring battery voltage. LTC1325's internal battery divider used, account must taken tolerance (±2%), well reference tolerance (±0.8%) tolerances bits/1024 bits 0.4%). system tolerance then ±3.2%. Adding resistor division ratio would bring this tolerance ±4.2%. Using ±0.1% external divider feeding into pin, resulting tolerance ±0.8% reference, plus ±0.5% represented divider resistors. design center charging voltage 4.19V. Overcharging effective voltage battery's terminals greater than 4.250V absolute maximum) strongly discouraged Li-Ion cell manufacturers. overcharging will shorten cell's life result catastrophic failure. With undivided battery voltage connected LTC1325's VBAT input, on-chip battery divider used check VCELL reaching FEDV (Fault: Discharge Voltage) point. There also need ensure that cell voltage rarely, ever, dips below 2.5V 2.7V (contact specific cell manufacturer details), that never goes below 1.0V. This spot where fail-safe capabilities LTC1325 serve Li-Ion user well.
AN64-31
Application Note
APPENDIX Flow Charts
START
CONDITIONING?
START DISCHARGE START TOP-OFF CHARGE LONG WAIT
READ STATUS
LONG WAIT
RESUME TOP-OFF CHARGE
IDLE MODE SHORT WAIT
START FAST CHARGE
READ STATUS
TERMINATE?
LONG WAIT
IDLE MODE SHORT WAIT
RESUME FAST CHARGE
IDLE MODE SHORT WAIT
READ STATUS
MORE CONDITIONING?
TERMINATE?
AN64 FB01
Figure Simplified Battery Management Flow Chart
AN64-32
Application Note
START
RESET MINUTE COUNTER
IDLE MODE MODE FSCLR FAST-CHARGE RATE TIME-OUT MIN.
DISPLAY STATUS MODE
CHARGE STARTED? CHARGE MODE MODE
STOP?
BATTERY PRESENT?
TERMINATE? ENABLE CONDITIONING
BATTERY REVERSED? DISCHARGE MODE MODE
CHARGE RATE FAST?
CHARGE RATE TOP-OFF COLD?
MORE CONDITIONING? DISABLE CONDITIONING
DISCHARGE? FAIL-SAFE TIME-OUT
CHARGE MODE MODE
CONDITIONING ENABLED?
TIME-OUT?
TIME-OUT?
INDICATE DEFECTIVE BATTERY
IDLE MODE MODE
AN64 FB02a
Figure B2a. Comprehensive Battery Management Flow Chart
AN64-33
Application Note
START
SAVE CURRENT MODE
READ SAVE USER SWITCHES
INCREMENT COUNTER
IDLE MODE MODE FSCLR
RESET MINUTE COUNTER
READ VCELL VOLTAGE
READ TBAT VOLTAGE
READ TAMB VOLTAGE STATUS
CALCULATE TERMINATION CRITERIA
RESTORE CURRENT MODE
RE-ENABLE INTERRUPTS
AN64 FB02b
Figure B2b. Timer Interrupt Service Routine Comprehensive Battery Management
AN64-34
Application Note
START CHARGING
READ VCELL
VCELL VCELL(MAX) 0.105C 0.315C 1.05C
CHARGE INCREASE IDLE READ VCELL
VCELL VCELL(MAX)
0.105C
VCELL (VCELL(MAX) 50mV)
0.315C
"CONTINUE" "DONE"
AN64 FB03a
Figure B3a. Constant-Potential Charging Algorithm Lead-Acid Li-Ion
AN64-35
Application Note
CONTINUE
DECREASE
1.05C
0.315C
0.105C
0.315C
CHARGE DONE (FROM P.1)
IDLE
READ VCELL
MODE GAUGE IDLE)
MONITOR BATTERY VCELL VCELL(MAX)
VCELL (VCELL(MAX) 50mV)
AN64 FB03b
Figure B3b. Constant-Potential Charging Algorithm Lead-Acid Li-Ion
AN64-36
Application Note
APPENDIX Brief Glossary with other field, rechargeable battery technique terminology. Here definitions which useful know. Also included terms used describe LTC1325, operation application circuits. Actual Capacity: capacity electrical energy storage cell which good condition, under test circumstances which differ from those established measurement cell's standard capacity. Battery: grouping cells, increase voltage (series), Ampere-Hour capability (parallel), both (series-parallel). this document, "battery" used interchangeably with "cell." Where differ, battery assumed series assembly cells unless otherwise specified. Battery Divider: programmable voltage divider (divide 1,2,.,16) connected between VBAT Sense pins LTC1325. battery types with cell voltages greater than 2.9V, necessary program divider keep divider output within 2.9V minimum range LTC1325 10-bit (Analog-to-Digital Converter). BATP: Battery Present Status Bit. status bits that LTC1325 provides. This when VBAT pulled below least 1.8V. BATR: Battery Reversed Battery Shorted Status Bit. status bits that LTC1325 provides. When cell voltage, VCELL less than 100mV, BATR discharging charging terminated. Current expressed terms rate battery, e.g., 1.2C, 0.1C, etc. Rate: normalization concept widely used battery community. rate unity equal capacity cell ampere-hours, divided hour. Hence Ampere-Hour cell rate (2.4 Ampere-Hours)/ Hour) Amperes. extension, 0.1C rate same cell equates (0.1) (2.4 Ampere-Hours)/ Hour) 0.24 Amperes, rate Amperes. value this term lies fact that, given cell type, behavior cells varying actual capacity will nonetheless very similar same rates. Cell: single electrochemical energy storage element. Cells come various technologies (e.g., Nickel-Cadmium Nickel-Metal Hydride) various Ampere-Hour ratings. Cell Reversal: situation involving lowest capacity cell battery stack, which manifest itself battery stack approaches deeply discharged state. given cell reaches condition zero charge before current draw from battery stack whole terminated, then current from other cells battery stack will force reverse charge onto cell question. This reverse charge, allowed continue significant length time, cause irreversible deterioration cell undergoing reversal. Charge Acceptance: ability battery transform charging energy form electrical current) into available energy form useful chemical reactions). Essentially, measure efficiency battery storage device electrical energy. This efficiency varies with battery temperature, state charge, charging rate, electrochemistry. Charge Mode: LTC1325 programmed into this functional mode charge batteries. Charging will commence terminated battery absent (see BATP) battery temperature outside permissible limits (see HTF) battery reversed shorted (see BATR) time-out condition exists. Charge Termination Method: means employed given charging algorithm determine appropriate point charging cycle which terminate phase that charging cycle. Current Cutoff (CCO): charge termination technique which monitors current level flowing into cell battery, indicates charging circuit that charging current should reduced when level falls below given limit. Cycle Life: number charge/discharge cycles which battery sustain before capacity declines specified percentage standard capacity, initial actual capacity given application. permissible percentage loss battery capacity fixed term
AN64-37
Application Note
within battery industry, most applications have their unique criteria. dTBAT/dt: Delta Temperature/Delta Time. Delta Temperature/Delta Time (T/t dTBAT/dt): Charge Termination Method Secondary Charge Termination Method) used terminate high-rate portion NiCd NiMH fast-charge regimen. This technique makes fact that case temperature cell undergoing high-rate charge will experience relatively rapid temperature rise goes into high-rate overcharge. When this rate rise reaches predetermined value (typically about 1°C/minute), almost dischargeable capacity been returned cell, high-rate charge should terminated. d2VBAT/dt2: Inflection Point Cutoff. Discharge Mode: LTC1325 programmed into this functional mode discharge batteries through external limiting resistor RDIS N-channel MOSFET. gate N-channel MOSFET driven pin. Discharge Profile voltage-vs-remaining charge characteristic cell battery; degree voltage change shown battery goes from being fully charged being fully discharged. Duty Cycle: LTC1325 programmed modulate "on" time charge loop with duty cycles 1/8, 1/4, period this modulation 42s. EDV: Discharge Voltage. Refers either status internal discharge voltage 0.9V. Discharge automatically terminated LTC1325 when cell voltage (VCELL) falls below 0.9V. Energy Density (W-H/kg): "figure-of-merit" term comparing differing battery technologies terms energy storage capacity mass (Watt-Hours/kg). Energy Density (W-H/L): "figure-of-merit" term comparing differing battery technologies terms energy storage capacity volume (Watt-Hours/Liter). Fail-Safes: Various protective measures (voltage, temperature time limits) built into LTC1325 protect battery against potentially damaging voltage temperature conditions when charge discharge modes. Also referred "Fault Protection." Fast-Charge: Generally, several charging regimens which capable completely recharging battery within three hours less. More importantly, such regimens typically return least battery's useable capacity within hour less. Only batteries specifically designed rated requirements imposed fastcharge applications should employed such applications. Gauging: Computation amount energy remaining battery. This typically done coulometric means, that current with which battery charged metered integrated. currents drawn battery then metered subtracted from integrated total. More sophisticated versions this same concept look-up tables and/or algorithmic means allow effects such variables charging rate, discharge rate, temperature during charge discharge phases battery use. These corrections compensate measurement discrepancies which battery's variable charge acceptance actual capacity might otherwise cause. Gauge: perform gauging function. Also, device display used somewhere within system employing gauging function, indicate status battery user and/or system software routines. Gauge Mode: LTC1325 programmed into this functional mode measure load currents sensed RSENSE. voltage across RSENSE multipled filtered before being converted ADC. filter consists internal resistor external nonpolarised capacitor CFILTER connected Filter LTC1325. Gassing: generation gas(ses) within cell approaches enters overcharge regime. Gassing anticipated part cell's operation, harmful unless rate gassing exceeds rate which cell recombine gas(ses) generated. Under such circumstances, excess gas(ses) will escape outside cell through pressure relief valve, causing permanent loss cell some electrolyte from which gas(ses) were evolved. High-Rate Charge: first stage more stage fast-charge regimen, during which current flowing
AN64-38
Application Note
through battery under charge greater rate than battery allow continuous basis. This portion fast-charge requires specific external termination. HTF: High Temperature Fault. Refers either status highest battery temperature which charging discharging permitted LTC1325. Charging automatically terminated LTC1325 when voltage TBAT less than voltage pin. ICHG: Average Charging Current. This should within recommended limits battery. IDIS: Average Discharge Current. This should within recommended limits battery. Idle Mode: LTC1325 programmed into this mode when none other modes needed make measurements without presence switching noise. Inflection Point Cutoff (d2VBAT/dt2): charge termination technique used with Nickel-Cadmium Nickel Metal Hydride batteries. During charge constant rate (e.g., high-current portion fast-charge regimen), terminal voltage such batteries increases until battery slightly into overcharge. rate this increase, however, linear with respect time. Shortly before battery reaches full charge, rate change terminal voltage becomes constant; time battery becomes fully charged this rate change becomes either zero negative. second derivative battery's voltage with respect time therefore used indicate that point which battery near full charge, looking either zero, more commonly negative, value d2VBAT/dt. Incremental Temperature Cutoff (TCO): Charge Termination Method Secondary Charge Termination Method) frequently used terminate high-rate portion fast-charge regimen. makes fact that case fully charged cell will experience relatively rapid temperature rise goes into high-rate overcharge (typically 0.5°C/minute 1°C/minute). LTF: Temperature Fault. Refers either status lowest battery temperature which charging discharging permitted LTC1325. Charging automatically terminated when voltage TBAT LTC1325 greater than voltage pin. MCV: Maximum Cell Voltage. Refers either status highest permissible VCELL. Charging automatically terminated LTC1325 when cell voltage (VCELL) greater than voltage pin. Negative Voltage Charge Termination Method Secondary Charge Termination Method) frequently used terminate high rate portion fast-charge regimen. This method makes fact that voltage across Nickel-Cadmium cell, lesser degree, Nickel-Metal Hydride cell, will experience maximum voltage subsequent voltage decrease (the once goes into high-rate overcharge (typically between 20mV 50mV Nickel-Cadmium cell). This technique most commonly employed with NiCd batteries. NiCd: Nickel-Cadmium NiMH: Nickel-Metal Hydride NTC: Negative Temperature Coefficient. Also used this Application Note refer thermistors with negative temperature coefficients. Overcharge: situation which arises when cell been returned state full charge, charging current cell removed. necessity, cells designed handle certain amount overcharge, hence, this necessarily either harmful undesirable condition. During overcharge, excess electrical energy applied cell which does towards preventing self-discharge dissipated heat, through formation recombination gas(ses) within cell. PTC: Positive Temperature Coefficient. Also used this Application Note refer thermistors with positive temperature coefficients. Quick-Charge: charging regimen Nickel-Cadmium Nickel-Metal Hydride batteries which return 100% usable capacity battery five hours. Batteries charged this manner must rated such charging. charging current this regimen usually stipulated manufacturer 0.33C.
AN64-39
Application Note
RDIS: External resistor LTC1325-based circuits limit battery discharge currents within recommended limits battery. RDS(ON): Drain source on-resistance MOSFET. Required Charging Voltage: minimum voltage which should available with which charge given type battery, given charge regimen. Essentially, compliance voltage capability charger, dictated voltage which battery expected achieve during charging cycle. RSENSE: Sense Resistor. external resistor LTC1325based circuits which connected between Sense ground. This resistor used sense battery current charge gauge modes. RTRK: Trickle Resistor. external resistor LTC1325based circuits. This resistor three purposes: keeps battery fully charged condition after charging completed, trickle-charges deeply discharged battery raise cell voltage above 100mV that charging commence, pulls VBAT high whenever battery removed. This tells LTC1325 that battery been removed. Secondary Charge Termination Methods: Certain charging algorithms, especially fast-charge algorithms, have potential damage batteries which they charging charge termination does occur properly. this reason, such algorithms generally employ more than termination method. Secondary Charge Termination Methods those which provide redundancy chosen Charge Termination Method. Self-Discharge: characteristic electrochemical storage cells bring themselves discharged state, even when their terminals open-circuited. Self-Discharge Rate: rate which electrochemical storage cell brings itself towards discharged state, with terminals open-circuited. This rate example, approximately 0.5%/day 1%/day Nickel-Cadmium Nickel-Metal Hydride cells room temperature. Shutdown Mode: LTC1325 programmed into this functional mode reduce current drain supply 30mA typical. Standard Capacity: capacity electrical energy storage cell which good condition. necessary tests ascertain this capacity carried under cell manufacturer's specified standard conditions, which generally those which cell expected deliver best performance. Standard-Charge: "overnight" charge method. This regimen typically involves charging 0.1C rate, requiring hours perform complete charge battery. TAMB: Refers ambient temperature TAMB LTC1325. This connected undedicated channel 10-bit used monitor ambient temperature. TBAT: Refers either battery temperature voltage TBAT LTC1325. Temperature Cutoff (TCO): technique determining what point terminate charging cell battery. absolute temperature cell cell battery) monitored temperature-sensitive element which, upon detecting preset temperature, will either reduce terminate charging current cell battery. frequently used backup termination method fast-charge systems. Time-Out: time limit charge discharge time. eight values: 160, minutes time-out. Top-Off Charge: second portion three-stage fast-charge regimen, during which rate current flow through battery under charge back significantly from high-rate value. This portion charge serves battery barely into overcharge. Trickle-Charge: third stage three-stage fastcharge regimen, during which rate current flow through battery under charge kept sufficient level prevent battery from self-discharging, which contributes little charging battery current level required trickle-charge lower than that used topoff-charge. VCELL: Cell Voltage. battery voltage divided programmed setting LTC1325 battery divider.
AN64-40
Application Note
VDAC: programmable reference voltage LTC1325 which determines average voltage Sense when LTC1325 programmed into charge mode. VDAC four values. VDC: Positive charging supply LTC1325 circuits described this Application Note. VDD: Positive supply LTC1325. Same voltages between 4.5V 16V. VEC: Charge Voltage. maximum voltage across each cell battery when fully charged. voltage should above prevent false failsafes from occurring. Venting: loss gas(ses) from inside nominally "sealed" cell ambient, through cell's pressure relief valve. Venting indicative harmful level overcharge, will cause eventual irreparable damage cell. VBAT: Battery Voltage VIN: Refers LTC1325 voltage. This connected undedicated channel 10-bit used monitor desired voltage within range ADC. Zero Voltage (Zero Charge Termination Method Secondary Charge Termination Method) frequently used terminate high-rate portion fast-charge regimen. This method makes fact that voltage across Nickel-Metal Hydride Nickel-Cadmium cell will experience voltage maximum, subsequent voltage decrease plateau once goes into high-rate overcharge. point which voltage stops increasing during charging point Zero This technique most commonly employed with NiMH batteries.
APPENDIX External Component Sources List Batteries Duracell (HQ) Berkshire Corporate Park Bethel, 06801 (203) 796-4000 (800) 243-9540 FAX: (203) 730-8958 Energizer Power Systems Div. Eveready Battery Co., Inc. Highway North P.O. 147114 Gainesville, 32614-7114 (904) 462-3911 FAX: (904) 462-6210 Batteries (U.S.A.) Inc, 2772 Loker Avenue West Carlsbad, 92008 (619) 438-2202 FAX: (619) 438-0694 Battery (USA) Inc. 17253 Chestnut Street City Industry, 91748 (818) 964-8348 FAX: (818) 810-9438 Hawker Energy Products, Inc. Ridgeview Drive Warrensburg, 64093-9301 (816) 429-2165 FAX: (816) 429-2253 Panasonic Industrial Company Headquarters: 1511 Secaucus, 07096 (201) 348-5272 FAX: (201) 392-4728 SAFT America, Inc. Otay Commerce Center 2155 Paseo Americas, Diego, 92173 (619) 661-7992 FAX: (619) 661-5096 SANYO Energy (U.S.A.) Corporation 2001 Sanyo Avenue Diego, 92173 (619) 661-6620 FAX: (619) 661-6743 Tadiran Electronic Industries, Inc. Seaview Boulevard Port Washington, 11050 (800) 786-9887 (516) 621-4980 FAX: (516) 621-4517
AN64-41
Application Note
Varta Batteries Inc. (USA) Executive Boulevard Elmsford, 10523-1202 (914) 592-2500 FAX: (914) 592-2667 Inductors Coiltronics, Inc. 6000 Park Commerce Boulevard Boca Raton, 33487 (407) 241-7876 FAX: (407) 241-9339 Dale Electronics, Inc. East Highway P.O. Yankton, 57078-0180 (605) 665-9301 FAX: (605) 665-1627 Hurricane Electronics P.O. 1280 North 2260 West Hurricane, 84737 (801) 635-2003 FAX: (801) 635-2495 Sumida Electric (USA) Corp., Ltd. 5999 Wilkie Road Suite Rolling Meadows, 60008 (847) 956-0666 FAX: (847) 956-0702 Thermistors Alpha Thermistor Assembly Inc. 7181 Construction Court Diego, 92121 (619) 549-4660 FAX: (619) 549-4791 Fenwal Electronics Inc. Fortune Boulevard Milford, 01757 (508) 478-6000 FAX: (508) 473-6035 Panasonic Industrial Company Panasonic Way, 7H-3 Secaucus, 07094 (201) 348-5232 FAX: (201) 392-4441 Phillips Components Discrete Products Division 2001 Blue Heron Blvd. P.O. 10330 Riviera Beach, 33404 (407) 881-3200 Thermometrics Inc. U.S. Highway Edison, 08817 (908) 287-2870 FAX: (908) 287-8847 MOSFETs International Rectifier U.S. World Headquarters Kansas Street Segundo, 90245 (310) 322-3331 FAX: (310) 322-3332 Motorola Semiconductor, Inc. 3102 North 56th Street MS56-126 Phoenix, 85018 (800) 521-6274 Siliconix Inc. 2201 Laurelwood Road P.O. 54951 Santa Clara, 95056 (408) 988-8000 FAX: (408) 970-3950 Schottky Diodes General Instrument Power Semiconductor Division Melville Park Road Melville, 11747 (516) 847-3000 International Rectifier U.S. World Headquarters Kansas Street Segundo, 90245 (310) 322-3331 FAX: (310) 322-3332 Motorola Semiconductor, Inc. 3102 North 56th Street MS56-126 Phoenix, 85018 (800) 521-6274 Polymer PTCs Raychem Corporation PolySwitch Division Constitution Drive Menlo Park, 94025-1164 (800) 272-9243, x6900 FAX: (800) 227-4866 Bimetallic Thermostats Phillips Technologies Airpax Protector Group Highland Avenue Frederick, 21701 (301) 663-5141 FAX: (301) 698-0624
AN64-42
Application Note
VOLTS AMPS
SELENIUM INDUSTRIES,
LOAD
AN64 FC01
Early Battery Management
SEMI-REGULATED
DC/DC CONVERTER(S)
INTERNAL POWER SUPPLY
PRECISION REFERENCE
SWITCHING CHARGER CONTROL
POWER SWITCHING CIRCUITRY
SYSTEM POWER MANAGEMENT
INTERFACE
ANALOG DIGITAL CONVERTER
BATTERY SENSOR SIGNAL CONDITIONING
VBAT TBAT TAMB SPARE HIGH
CONTROL LOGIC
DIGITAL ANALOG CONVERTER
"HARD WIRED" FAIL-SAFES
HIGH LONG
BATTERY
GAUGE CIRCUITRY
LTC1325 POWER SUPPLY ENABLES SYSTEM LOAD ENABLES
AN64 FC02
Modern Battery Management
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
AN64-43
Application Note
U.S. Area Sales Offices
NORTHEAST REGION Linear Technology Corporation 3220 Tillman Drive, Suite Bensalem, 19020 Phone: (215) 638-9667 FAX: (215) 638-9764 Linear Technology Corporation Lowell Street, Suite Wilmington, 01887 Phone: (508) 658-3881 FAX: (508) 658-2701 NORTHWEST REGION Linear Technology Corporation 1900 McCarthy Blvd., Suite Milpitas, 95035 Phone: (408) 428-2050 FAX: (408) 432-6331 SOUTHEAST REGION Linear Technology Corporation 17000 Dallas Parkway, Suite Dallas, 75248 Phone: (214) 733-3071 FAX: (214) 380-5138 Linear Technology Corporation 5510 Forks Road, Suite Raleigh, 27609 Phone: (919) 870-5106 FAX: (919) 870-8831 CENTRAL REGION Linear Technology Corporation Chesapeake Square Mitchell Court, Suite A-25 Addison, 60101 Phone: (708) 620-6910 FAX: (708) 620-6977 SOUTHWEST REGION Linear Technology Corporation 21243 Ventura Blvd., Suite Woodland Hills, 91364 Phone: (818) 703-0835 FAX: (818) 703-0517 Linear Technology Corporation 15375 Barranca Parkway, Suite A-211 Irvine, 92718 Phone: (714) 453-4650 FAX: (714) 453-4765
International Sales Offices
FRANCE Linear Technology S.A.R.L. Immeuble Quartz" Chemin Justice 92290 Chatenay Malabry France Phone: 33-1-41079555 FAX: 33-1-46314613 GERMANY Linear Technology GmbH Oskar-Messter-Str. 85737 Ismaning Germany Phone: 49-89-962455-0 FAX: 49-89-963147 JAPAN Linear Technology Bldg. 1-14 Shin-Ogawa-cho Shinjuku-ku Tokyo, Japan Phone: 81-3-3267-7891 FAX: 81-3-3267-8510 KOREA Linear Technology Korea Co., Namsong Building, #403 Itaewon-Dong 260-199 Yongsan-Ku, Seoul 140-200 Korea Phone: 82-2-792-1617 FAX: 82-2-792-1619 SINGAPORE Linear Technology Pte. Ltd. Yishun Industrial Park Singapore 2776 Phone: 65-753-2692 FAX: 65-754-4113 SWEDEN Linear Technology S-191 Sollentuna Sweden Phone: 46-8-623-1600 FAX: 46-8-623-1650 TAIWAN Linear Technology Corporation 602, Sec. Chung Shan Taipei, Taiwan, R.O.C. Phone: 886-2-521-7575 FAX: 886-2-562-2285 UNITED KINGDOM Linear Technology (UK) Ltd. Coliseum, Riverside Camberley, Surrey GU15 United Kingdom Phone: 44-1276-677676 FAX: 44-1276-64851
World Headquarters
Linear Technology Corporation 1630 McCarthy Blvd. Milpitas, 95035-7417 Phone: (408) 432-1900 FAX: (408) 434-0507
0896
Linear Technology Corporation
LT/GP 0896 PRINTED
AN64-44
1630 McCarthy Blvd., Milpitas, 95035-7417
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
LINEAR TECHNOLOGY CORPORATION 1994
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