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LT1769 Constant-Current/ Constant-Voltage Battery Charger with Input Current Limiting DESCRIPTIO
LT®1769 current mode battery charger simple, efficient solution fast charge modern rechargeable batteries including lithium-ion (Li-Ion), nickel-metalhydride (NiMH) nickel-cadmium (NiCd) that require constant-current and/or constant-voltage charging. internal switch capable delivering 2A** current peak current). Charge current programmed resistors within With 0.5% reference voltage accuracy, LT1769 meets critical constant-voltage charging requirement Li-Ion cells. third control loop provided regulate current drawn from input adapter. This allows simultaneous operation equipment battery charging without overloading adapter. Charge current reduced keep adapter current below specified levels. LT1769 charge batteries ranging from 20V. Ground sensing current required battery's negative terminal tied directly ground. saturating switch running 200kHz gives high charging efficiency small inductor size. blocking diode required between chip battery because chip goes into sleep mode drains only when wall adapter unplugged.
Simple Solution Charge NiCd, NiMH Lithium Rechargeable Batteries-Charging Current Programmed Resistors Adapter Current Limit Allows Maximum Possible Charging Current During System Use* Precision 0.5% Accuracy Voltage Mode Charging Available 20-Lead Exposed TSSOP 28-Lead Narrow SSOP Packages High Efficiency Current Mode with Internal Switch Charge Current Accuracy Adjustable Undervoltage Lockout Automatic Shutdown When Adapter Removed Reverse Battery Drain Current: Current Sensing Either Terminal Battery Charging Current Soft Start Shutdown Control
APPLICATIO
Chargers NiCd, NiMH, Lead-Acid, Lithium Rechargeable Batteries Switching Regulators with Precision Current Limit
registered trademarks Linear Technology Corporation. patent number 5,723,970 **See LT1510 1.5A charger; LT1511 charger
TYPICAL APPLICATIO
SS24
BOOST LT1769 COMP1 SPIN SENSE PROG 390k 0.25% BATTERY VOLTAGE SENSE 162k 0.25% 0.33µF CPROG RPROG 4.93k CIN* 15µF
0.47µF L1** 22µH 1N4148
NOTE: COMPLETE LITHIUM-ION CHARGER, TERMINATION REQUIRED. RS4, OPTIONAL LIMITING *TOKIN UNITED CHEMI-CON/MARCON CERAMIC SURFACE MOUNT **22µH SUMIDA CDRH125 APPLICATIONS INFORMATION INPUT CURRENT LIMIT UNDERVOLTAGE LOCKOUT GENERAL SEMICONDUCTOR. LESS THEN 100°C MBRS130LT3 USED
0.05 BATTERY CURRENT SENSE
COUT 22µF TANT
Figure Lithium-Ion Battery Charger
SS24 ADAPTER CURRENT SENSE (ADAPTER INPUT) MAIN SYSTEM LOAD UNDERVOLTAGE LOCKOUT
VBAT 8.4V Li-Ion
1511
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LT1769
ABSOLUTE MAXIMUM RATINGS (Note
Supply Voltage (VCC, Voltage) BOOST Voltage with Respect IBAT (Average). Operating Junction Temperature Range Commercial 125°C Industrial 40°C 125°C Operating Ambient Temperature Commercial 70°C Industrial 40°C 85°C Storage Temperature Range 65°C 150°C Lead Temperature (Soldering, sec). 300°C
PACKAGE/ORDER INFORMATION
VIEW GND** GND** GND** BOOST GND** GND** GND** GND** GND** VCC1* VCC2* VCC3* GND** PROG UVOUT COMP2 SPIN GND**
ORDER PART NUMBER LT1769CGN LT1769IGN
BOOST
COMP1 SENSE GND**
PACKAGE 28-LEAD PLASTIC SSOP
TJMAX 125°C, 35°C/
*ALL PINS SHOULD CONNECTED TOGETHER CLOSE PINS PINS FUSED INTERNAL ATTACH PADDLE HEAT SINKING. CONNECT THESE PINS EXPANDED LANDS PROPER HEAT SINKING. 35°C/W THERMAL RESISTANCE ASSUMES INTERNAL GROUND PLANE DOUBLING HEAT SPREADER
Consult Marketing parts specified with wider operating temperature ranges.
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 16V, VBAT (see Block Diagram), VCLN VCC. load outputs unless otherwise noted.
PARAMETER Overall Supply Current Sense Amplifier Gain Input Offset Voltage (With 200, 200) (Measured across RS1)(Note VPROG 2.7V, VPROG 2.7V, VBAT RPROG 4.93k RPROG 49.3k 28V, VBAT RPROG 4.93k RPROG 49.3k
ELECTRICAL CHARACTERISTICS
CONDITIONS
VIEW VCC1 VCC2 VCC3 PROG UVOUT SPIN
ORDER PART NUMBER LT1769CFE LT1769IFE
COMP1
SENSE
PACKAGE 20-LEAD PLASTIC TSSOP
BOTTOM METAL
TJMAX 125°C, 35°C/ EXPOSED GROUND (MUST SOLDERED PCB) EXPOSED SIZE: (.188) (.162)
PLATE THIS PACKAGE FUSED INTERNAL GROUND HEAT SINKING. SOLDER BOTTOM METAL PLATE ONTO GROUND PLANE HEAT SINKING.
UNITS
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LT1769
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 16V, VBAT (see Block Diagram), VCLN VCC. load outputs unless otherwise noted.
PARAMETER Overall Undervoltage Lockout (Switch OFF) Threshold Input Current Output Voltage UVOUT Output Leakage Current UVOUT Reverse Current from Battery (When Connected, Floating) Boost Current Measured 0.2V Undervoltage State, IUVOUT 70µA VUV, VUVOUT VBAT 20V, 0.4V 20V, VBOOST 28V, VBOOST VBOOST (Switch VBOOST (Switch VMAX, VBOOST VBOOST 24V,
ELECTRICAL CHARACTERISTICS
CONDITIONS
0.25
UNITS
Switch Switch Resistance IBOOST/ISW During Switch Switch Leakage Current Minimum IPROG Switch Minimum IPROG Switch Maximum VBAT Switch Current Sense Amplifier Inputs (Sense, BAT) Input Bias Current Input Common Mode Input Common Mode High SPIN Input Current Reference Reference Voltage (Note Reference Voltage Oscillator Switching Frequency Switching Frequency Maximum Duty Cycle
0.15
0.25
mA/A
0.25
RPROG 4.93k, Measured with Supplying IPROG Switch Conditions VCC, (Note
2.448 2.441 2.43
2.465
2.477 2.489 2.489
Conditions VCC,
Current Amplifier Transconductance Maximum Switch Current (Out Pin) 0.6V 0.45V ±1µA
µmho
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LT1769
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. 16V, VBAT load outputs unless otherwise noted.
PARAMETER Voltage Amplifier Transconductance (Note Output Source Current Input Bias Current Output Current from 50µA 500µA VOVP VREF 10mV, VPROG VREF 10mV Output Current 0.5mA Output Current 0.5mA, 90°C Output Current 0.5mA,
ELECTRICAL CHARACTERISTICS
CONDITIONS
UNITS
0.25
Current Limit Amplifier CL1, Input Common Mode Turn-On Threshold Transconductance Input Current Input Current 0.5mA Output Current Output Current from 50µA 500µA 0.5mA Output Current, 0.4V 0.5mA Output Current 0.4V
Note Absolute Maximum Ratings those values beyond which life device impaired. Note Tested with Test Circuit
Note Tested with Test Circuit Note linear interpolation used reference voltage specification between 40°C.
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency Figure Circuit
16.5 VBAT 8.4V
EFFICIENCY
(mA)
CHARGER EFFICIENCY
(mA)
INCLUDES LOSS DIODE
IBAT
1769
Duty Cycle
MAXIMUM DUTY CYCLE 25°C
125°C 25°C
125°C
DUTY CYCLE
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LT1769 TYPICAL PERFORMANCE CHARACTERISTICS
VREF Line Regulation
0.003 0.002
0.001
VREF
VOVP (mV)
-0.001
-0.002 -0.003
Maximum Duty Cycle
-1.20 -1.08 -0.96 -0.84 -0.72
DUTY CYCLE
(mA)
JUNCTION TEMPERATURE (°C)
PROG Characteristic6
125°C
REFERENCE VOLTAGE
IPROG (mA)
VPROG
1769
VOVP (Voltage Amplifier)
TEMPERATURES
125°C
25°C
1769
(mA)
1769
Characteristic
-0.60 -0.48 -0.36 -0.24 -0.12 0.12
1769
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Reference Voltage Temperature
2.470 2.468 2.466 2.464 2.462 2.460 2.458 JUNCTION TEMPERATURE
25°C
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LT1769
FUNCTIONS
(Pins 28/Pins 20): Ground Pins. Must connected expanded lands proper heat sinking. Applications Information section details. (Pin 4/Pin Switch Output. Schottky catch diode must placed with very short lead length close proximity GND. BOOST (Pin 5/Pin This used bootstrap drive switch power transistor on-voltage power dissipation. Figure VBOOST VBAT when switch lowest power dissipation, connect boost diode 30mA voltage source (see Figure 10). (Pin 6/Pin Undervoltage Lockout Input. rising threshold 6.7V with hysteresis 0.5V. Switching stops undervoltage lockout. When input supply (normally wall adapter output) removed, must pulled down below 0.7V resistor from adapter output required) otherwise reverse battery current drained will approximately 200µA instead 3µA. leave floating. When connected with resistor divider, built-in 6.7V undervoltage lockout will effective. (Pin 9/Pin This input amplifier with threshold 2.465V. Typical bias current about this pin. charging lithium-ion batteries, monitors battery voltage reduces charging when battery voltage reaches preset value. used, should grounded. (Pin 10/Pin This positive input input current limit amplifier CL1. threshold 100mV. When used limit supply current, filter needed filter 200kHz switching noise. (Pin 11/Pin This negative input input current limit amplifier CL1. COMP1 (Pin 12/Pin This compensation node input current limit amplifier CL1. input adapter current limit, this node rises forcing COMP1 with external transistor, amplifier will defeated adapter current limit). COMP1 source 200µA.
(GN/FE Numbers)
this function used, resistor capacitor COMP1 pin, shown Figure circuit, needed. SENSE (Pin 13/Pin 10): Current Amplifier Input. Sensing either terminal battery. SPIN (Pin 16/Pin 11): This current amplifier bias. must connected shown Lithium Battery Charger (Figure (Pin 17/Pin 12): Current Amplifier Input. COMP2 (Pin 18): This also compensation node amplifier CL1. Voltage this rises 2.8V input adapter current limit and/or constant-voltage charging. UVOUT (Pin 19/Pin 13): This open-collector output undervoltage lockout status. stays undervoltage state. With external pull-up resistor, goes high valid VCC. Note that base drive open-collector comes from pin. UVOUT stays only when higher than Pull-up current should kept under 100µA. (Pin 20/Pin 15): This inner loop control signal current mode PWM. Switching starts 0.7V. normal operation, higher corresponds higher charge current. capacitor least 0.33µF filters noise controls rate soft start. stop switching, pull this low. Typical output current 30µA. PROG (Pin 21/Pin 16): This programming charge current system loop compensation. During normal operation, VPROG stays close 2.465V. shorted switching will stop. When microprocessor controlled used program charge current, must capable sinking current compliance 2.465V. VCC1, VCC2, VCC3 (Pins 25/Pins 19): Input Supply. good bypass, capacitor 15µF higher required, with lead length kept minimum. should between least higher than VBAT. Undervoltage lockout starts switching stops when goes below typical. Note that there internal parasitic diode from pin. force below more than 0.7V with battery present. three pins should shorted together close pins.
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LT1769
BLOCK DIAGRAM
200kHz OSCILLATOR SHUTDOWN BOOST
0.7V
1.5V VBAT
VREF 0.64
UVOUT SLOPE COMPENSATION SPIN SENSE IBAT
IPROG
VREF 2.465V 100mV
COMP1 COMP2
PROG IPROG RPROG
CPROG
IBAT PROG 2.465V RPROG (RS3 RS2)
1769
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LT1769
TEST CIRCUITS
Test Circuit
SPIN LT1769 SENSE
VREF
0.047µF
LT1006
1769 TC01
0.65V
LT1769
IPROG
0.47µF
RPROG
2.465V
1769 TC02
OPERATION
LT1769 current mode step-down (buck) switcher. battery charge current programmed resistor RPROG output current) PROG (see Block Diagram). Amplifier converts charge current through much lower current IPROG into PROG pin. Amplifier compares output with programmed current drives control loop force them equal. High accuracy achieved with averaging capacitor CPROG. Note that IPROG both components. IPROG goes through generates ramp signal that control comparator through buffer level shift resistors forming current mode inner loop. BOOST drives switch into saturation reduces power loss. batteries like lithium-ion that require both constant-current constant-voltage charging, 0.5%, 2.465V reference amplifier reduce charge current when battery voltage reaches preset level. NiMH NiCd, used overvoltage protection. When input voltage removed, drops 0.7V below battery voltage, forcing charger into battery drain (3µA typical) sleep mode. shut down charger, simply pull with transistor.
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RPROG
PROG
VBAT
PROG
Test Circuit
VREF
LT1013
LT1769
APPLICATIONS INFORMATION
Input Output Capacitors Lithium-Ion Battery Charger (Figure input capacitor (CIN) assumed absorb input switching ripple current converter, must have adequate ripple current rating. Worst-case ripple current will equal half output charge current. Actual capacitance value critical. Solid tantalum capacitors such Sprague 593D series have high ripple current rating relatively small surface mount package, caution must used when tantalum capacitors used input bypass. High input surge currents possible when adapter hot-plugged charger solid tantalum capacitors have known failure mechanism when subjected very high turn-on surge currents. Selecting high voltage rating capacitor will minimize problems. Consult with manufacturer before use. Alternatives include high capacity ceramic (5µF 20µF) from Tokin United Chemi-Con/ Marcon, Sanyo OS-CON also used. output capacitor (COUT) also assumed absorb output switching ripple current. general formula capacitor ripple current
0.29 (VBAT) IRMS (L1)(f)
example, 16V, VBAT 8.4V, 20µH, 200kHz, IRMS 0.3A. considerations usually make desirable minimize ripple current battery leads. Beads inductors added increase battery impedance 200kHz switching frequency. Switching ripple current splits between battery output capacitor depending output capacitor battery impedance. COUT battery impedance raised with bead inductor, only ripple current will flow into battery. Soft-Start Undervoltage Lockout LT1769 soft-started 0.33µF capacitor pin. start-up, voltage will quickly rise 0.5V, then ramp rate internal 45µA pull-up current external capacitor. Charge current start
ramping when voltage reaches 0.7V full current achieved with 1.1V. With 0.33µF capacitor, time reach full charge current about 10ms assumed that input voltage charger will reach full value less than 10ms. capacitor increased longer input start-up times needed. switching regulator, conventional time-based softstarting defeated input voltage rises much slower than time period. This happens because switching regulators battery charger computer power supply typically supplying fixed amount power load. input voltage comes slowly compared soft-start time, regulators will deliver full power load when input voltage still well below final value. adapter current limited, cannot deliver full power reduced output voltages possibility exists quasi "latch" state where adapter output stays current limited state reduced output voltage. instance, maximum charger plus computer load power 25W, adapter might current limited adapter voltage less than (25W/2A 12.5V) when full power drawn, adapter voltage will pulled down constant load until reaches lower stable state where switching regulators longer supply full load. This situation prevented utilizing undervoltage lockout, higher than minimum adapter voltage where full power achieved. fixed undervoltage lockout built into LT1769. This threshold increased adding resistive divider shown Figure Internal lockout performed clamping low. released from clamped state when rises above pulled when drops below 6.5V (0.5V hysteresis). same time UVOUT goes high with external pull-up resistor. This signal used alert system that charging about start. charger will start delivering current about after released, 0.33µF capacitor. resistor divider used desired lockout voltage shown Figure typical value found from: R6(VIN
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LT1769
APPLICATIONS INFORMATION
Rising lockout threshold Charger input voltage that will sustain full load power Example: With 6.7V setting 12V; (12V 6.7V)/6.7V resistor divider should connected directly adapter output shown, pin, prevent battery drain with adapter voltage. used, connect adapter output (not VCC) connect resistor greater than ground. Floating this will cause reverse battery current increase from 200µA. connecting unused adapter output possible, grounded. Although would seem that grounding creates permanent lockout state, circuitry arranged phase reversal with voltages allow grounding technique work.
100mV
ADAPTER OUTPUT
RS4*
LT1769 *RS4 100mV ADAPTER CURRENT LIMIT
1769
Figure Adapter Input Current Limiting
Adapter Current Limiting important feature LT1769 ability automatically adjust charge current level which avoids overloading wall adapter. This allows product operate same time batteries being charged without complex load management algorithms. Additionally, batteries will automatically charged maximum possible rate which adapter capable. This accomplished sensing total adapter output current adjusting charge current downward preset adapter current limit exceeded. True analog control used, with closed-loop feedback ensuring that
adapter load current remains below limit. Amplifier Figure senses voltage across RS4, connected between pins. When this voltage exceeds 100mV, amplifier will override programmed charge current limit adapter current 100mV/RS4. lowpass filter formed required eliminate switching noise. input current limit used, both pins should connected VCC. Charge Current Programming basic formula charge current (see Block Diagram):
IBAT IPROG
2.465V RPROG
where RPROG total resistance from PROG ground. sense amplifier biasing purpose, should have same value SPIN should connected directly sense resistor (RS1) shown Block Diagram. example, charge current needed. power dissipation enough signal drive amplifier CA1, 100mV/2A 0.05. This limits power 0.2W. RPROG then:
PROG 2.465V (2A)(5k)(0.05) 2.465V
Charge current also programmed pulse width modulating IPROG with switch RPROG frequency higher than (Figure Charge current will proportional duty cycle switch with full current 100% duty cycle. Lithium-Ion Charging Lithium-Ion Battery Charger (Figure charges constant until battery voltage reaches limit charger will then automatically into constant-voltage mode with current decreasing near zero over time battery reaches full charge. This normal regimen lithium-ion charging, with charger
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LT1769
APPLICATIONS INFORMATION
LT1769 PROG
LT1769 VN2222 0.25%
RPROG 4.7k VN2222
CPROG
IBAT (DC)(2A)
1769
Figure Current Programming
holding battery "float" voltage indefinitely. this case external sensing full charge needed. Battery Voltage Sense Resistors Selection minimize battery drain when charger off, current through R3/R4 divider 15µA. input current error neglected. With divider current 15µA, VBAT 8.4V, 2.465/15µA 162k and,
(R4)(VBAT 2.465) 162k (8.4 2.465)
2.465 2.465
390k
Li-Ion batteries typically require float voltage accuracy Accuracy LT1769 voltage ±0.5% 25°C over full temperature. This leads possibility that very accurate (0.1%) resistors might needed Actually, temperature LT1769 will rarely exceed 50°C float mode because charging currents have tapered level, 0.25% resistors will normally provide required level overall accuracy. When power there about 200µA current flowing SENSE pins. battery removed during charging, total load including less than 200µA, VBAT could float even though loop turned switching off. keep VBAT regulated battery voltage this condition, chosen draw 0.5mA added disconnect them when power (Figure isolates from high frequency noise VIN. alternative method
8.4V
VBAT
220k 4.99k 0.25%
1769
Figure Disconnecting Voltage Divider
Zener diode with breakdown voltage three volts higher than battery voltage clamp VBAT voltage. Battery manufacturers recommend terminating constant-voltage float mode after charge current dropped below specified level (typically around full current) further time period minutes elapsed. This extend battery life, check with manufacturer details. circuit Figure will detect when charge current dropped below 270mA. This logic signal used initiate timeout period, after which LT1769 shut down pulling with open collector drain. Some external means must used detect need additional charging
IBAT SENSE 0.05 LT1769 VBAT 1.6k 0.1µF ADAPTER OUTPUT
3.3V 470k NEGATIVE EDGE TIMER
1N4148
LT1011 560k 430k 1N4148
TRIP CURRENT
R1(VBAT) R3)(RS1)
(1.6k)(8.4V) 270mA (560k 430k)(0.05)
1769
Figure Current Comparator Initiating Float Time
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LT1769
APPLICATIONS INFORMATION
charger turned periodically complete short float-voltage cycle. Current trip level determined battery voltage, through sense resistor (RS1). generates hysteresis trip level avoid multiple comparator transitions. Nickel-Cadmium Nickel-Metal-Hydride Charging Lithium-Ion Battery Charger shown Figure modified charge NiCd NiMH batteries. example, 2-level charge needed; when 100mA when off.
LT1769 PROG 49.3k 5.49k
1769
Figure 2-Level Charging
full current, current sense resistor (RS1) should increased that enough signal (10mV) will across 0.1A trickle charge keep charging current accurate. 2-level charger, found from:
(2.465)(2000
ILOW
(2.465)(2000
ILOW
battery chargers with fast charge rates require some means detect full charge battery terminate high charge current. NiCd batteries typically charged high current until temperature rise battery voltage decrease detected indication near full charge. charging current then reduced much lower value maintained constant trickle charge. intermediate "top off" current also used fixed time period reduce total charge time. NiMH batteries similar chemistry NiCd have differences related charging. First, inflection characteristic battery voltage full charge approached
nearly pronounced. This makes more difficult dV/dt indicator full charge, increase battery temperature more often used with temperature sensor battery pack. Secondly, constant trickle charge recommended. Instead, moderate level current used pulse basis duty cycle) with time-averaged value substituting constant trickle. Please contact Linear Technology Applications department about charge termination circuits. overvoltage protection needed, calculated according procedure described LithiumIon Charging section. should grounded used. When microprocessor output used control charge current, must capable sinking current compliance 2.5V connected directly PROG pin. Thermal Calculations LT1769 used charging currents above thermal calculation should done ensure that junction temperature will exceed 125°C. Power dissipation caused bias driver current, switch resistance switch transition losses. package, with thermal resistance 35°C/W, provide full charging current many situations. graph shown Typical Performance Characteristics section.
PBIAS (3.5mA )(VIN) 1.5mA(VBAT
(VBAT
[7.5mA (0.012)(IBAT
(IBAT )(VBAT VBAT PDRIVER 55(VIN) (IBAT (RSW )(VBAT OL)( IN)(
Switch resistance 0.16 Effective switch overlap time 10ns 200kHz
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LT1769
APPLICATIONS INFORMATION
Example: 19V, VBAT 12.6V, IBAT
PBIAS (3.5mA )(19) 1.5mA(12.6)
SPIN LT1769 BOOST
(12.6)2
[7.5mA (0.012)(2000mA)] 0.35W
(2)(12.6)2 12.6 0.43W PDRIVER 55(19) (2)2 (0.16)(12.6) 10-9 200kHz
0.42 0.08 0.5W
Total Power 0.35 0.43 1.3W Temperature rise will (1.3W)(35°C/W) 46°C. This assumes that LT1769 properly heat sunk connecting eleven fused ground pins expanded traces that board backside internal plane heat spreading. PDRIVER term reduced connecting boost diode (see Figure lower system voltage (lower than VBAT) instead VBAT.
(IBAT )(VBAT )(VX Then PDRIVER 55(VIN
example, 3.3V then:
(2A)(12.6V)(3.3V) 330V 0.09 55(19V
PDRIVER
average required PDRIVER 0.09 28mA 3.3V previous example shows dramatic drop driver power dissipation when boost diode (D2) connected external 3.3V source instead 12.6V battery. PDRIVER drops from 0.43W 0.09W resulting approximately 12°C drop junction temperature. Fused-lead packages conduct most their heat leads. This makes very important provide much board copper around leads practical. Total
10µF
1769
Figure Lower VBOOST
thermal resistance package-board combination dominated characteristics board immediate area package. This means both lateral thermal resistance across board vertical thermal resistance through board other copper layers. Each layer acts thermal heat spreader that increases heat sinking effectiveness extended areas board. Total board area becomes important factor when area board drops below about square inches. graph Figure shows thermal resistance board area 2-layer 4-layer boards with continuous copper planes. Note that 4-layer boards have significantly lower thermal resistance, both types show rapid increase reduced board areas. Figure shows actual measured lead temperatures chargers operating full current. Battery voltage input voltage will affect device power dissipation, data sheet power calculations must used extrapolate these readings other situations. Vias should used connect board layers together. Planes under charger area away from rest board connected with vias form both thermal resistance system ground plane reduced EMI. Glue-on, chip-mounted heat sinks effective only moderate power applications where board copper cannot used, where board size small. They offer very little improvement properly laid multilayer board reasonable size. Higher Duty Cycle LT1769 Battery Charger Maximum duty cycle LT1769 typically 90%, this some applications. example,
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LT1769
APPLICATIONS INFORMATION
BOARD AREA (IN2)
1769
THERMAL RESISTANCE (°C/W)
2-LAYER BOARD
4-LAYER BOARD MEASURED FROM AMBIENT USING COPPER LANDS SHOWN DATA SHEET
Figure LT1769 Thermal Resistance
HIGH DUTY CYCLE CONNECTION LEAD TEMPERATURE PINS (°C) NOTE: PEAK TEMPERATURE WILL ABOUT 15°C HIGHER CHARGE CURRENT VBAT 12.3V VBOOST 2-LAYER BOARD ROOM TEMP 24°C BOARD
BOARD Si4435DY TP0610L
CHARGE CURRENT
1769 1769
Figure LT1769 Lead Temperature
adapter used charge NiMH cells, charger must approximaly 15V. total 1.6V lost input diode, switch resistance, inductor resistance parasitics, required duty cycle 15/16.4 91.4%. duty cycle extended restricting boost voltage instead using VBAT normally done. This lower boost voltage also reduces power dissipation LT1769, win-win decision. Connect external source node Figure with 10µF bypass capacitor. Lower Dropout Voltage even lower dropout and/or reducing heat board, input diode replaced with (see Figure 11). Connect P-channel place input diode
STANDARD CONNECTION BOOST LT1769 SPIN SENSE
HIGH DUTY CYCLE CONNECTION BOOST LT1769 SPIN SENSE 10µF VBAT
0.47µF
0.47µF
VBAT
1769
Figure High Duty Cycle
0.47µF
BOOST LT1769 SPIN SENSE
10µF
VBAT
Figure Replacing Input Diode
with gate connected battery causing turn when input voltage goes low. problem that gate must pumped that fully turned even when input only volt above battery voltage. Also there turn-off speed issue. should turn instantly when input dead shorted avoid large current surges from battery back through charger into FET. Gate capacitance slows turn-off, small P-channel (Q2) added discharge gate capacitance quickly event input short. body diode creates necessary pumping action keep gate during normal operation. Note that have spec limit 20V. This restricts maximum 20V. dropout operation with consult factory.
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LT1769
APPLICATIONS INFORMATION
Optional Diode Connections typical application Figure shows single diode (D3) isolate from adaptor input block reverse input voltage (both steady state transient). This simple connection unacceptable situations where system load must powered from battery when adapter input power removed. shown Figure parasitic diode exists from LT1769. When input power removed, this diode will become forward biased will provide current path from battery system load. Because diode power limitations, recommended power system load through internal parasitic diode. safely power system load from battery, additional Schottky diode (D4) needed. minimum losses, could replaced RDS(ON) MOSFET which turned when adapter power removed.
LT1769 ADAPTER SYSTEM LOAD HIGH FREQUENCY CIRCULATING PATH
INTERNAL PARASITIC DIODE
1769 F12a 1769
Figure Modified Diode Connection
NOTE: CONNECT PINS EXPANDED LANDS PROPER HEAT SINKING
Figure Critical Electrical Thermal Path Layout
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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.
Layout Considerations Switch rise fall times under 10ns maximum efficiency. minimize radiation, catch diode, input bypass capacitor leads should kept short possible. ground plane should used under switching circuitry prevent interplane coupling thermal spreading path. ground pins should connected expanded traces thermal resistance. fast-switching high current ground path, including switch, catch diode input capacitor, should kept very short. Catch diode input capacitor should close chip terminated same point. This path contains nanosecond rise fall times with several amps current. other paths contain only and/or 200kHz tri-wave less critical. Figure indicates high speed, high current switching path. Figure shows critical path layout. Contact Linear Technology LT1769 circuit layout Gerber file.
SWITCH NODE VBAT
COUT
Figure High Speed Switching Path
BOOST COMP1 SENSE VCC1 VCC2 VCC3 PROG UVOUT COMP2 SPIN
COUT
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LT1769
PACKAGE DESCRIPTION
Package 20-Lead Plastic TSSOP (4.4mm)
(Reference 05-08-1663)
3.86 (.152)
6.60 ±0.10 4.50 ±0.10 NOTE
0.45 ±0.05 1.05 ±0.10 0.65 RECOMMENDED SOLDER LAYOUT 4.30 4.50* (.169 .177) 1.20 (.047) 6.40 6.60* (.252 .260) 3.86 (.152) 1918
0.09 0.20 (.0036 .0079)
0.45 0.75 (.018 .030)
NOTE: CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS DIMENSIONS (INCHES) DRAWING SCALE
0.015 0.004 (0.38 0.10) 0.0075 0.0098 (0.191 0.249) 0.016 0.050 (0.406 1.270)
0.053 0.069 (1.351 1.748)
0.008 0.012 (0.203 0.305)
DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.006" (0.152mm) SIDE DIMENSION DOES INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL EXCEED 0.010" (0.254mm) SIDE
RELATED PARTS
PART NUMBER LT1372/LT1377 LT1376 LT1505 LT1510 LT1511 LT1512/LT1513 LTC1729 LTC1759 LTC1960 DESCRIPTION 500kHz/1MHz Step-Up Switching Regulators 500kHz Step-Down Switching Regulator High Current, High Efficiency Battery Charger Battery Charger Battery Charger SEPIC Battery Chargers Li-Ion Battery Charger Termination Controller SMBus Smart Battery Charger Dual Battery Charger Selector with Interface COMMENTS High Frequency, Small Inductor, High Efficiency Switchers, 1.5A Switch High Frequency, Small Inductor, High Efficiency Switcher, 1.5A Switch Efficiency, Synchronous Current Mode 1.5A Charge Current Lithium-Ion, NiCd NiMH Batteries Charge Current Lithium-Ion, NiCd NiMH Batteries Higher Lower Than Battery Voltage Preconditioning Cell 2.7V, Time-Out, C/10 Detection, Temp Sensor Pin, Charger Battery Detection Efficiency with Input Current Limiting, ICHG ICHARGE Fast Charge, Longer Battery Life, Crisis Management
1769fa LT/TP 1101 1.5K PRINTED
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, 95035-7417
(408) 432-1900 FAX: (408) 434-0507
Exposed Variation
2.74 (.108)
0.65 (.0256)
0.195 0.30 (.0077 .0118)
0.05 0.15 (.002 .006)
2.74 6.40 (.108)
RECOMMENDED MINIMUM METAL SIZE EXPOSED ATTACHMENT *DIMENSIONS INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.150mm (.006") SIDE
FE20 (CB) TSSOP 0203
Package 28-Lead Plastic SSOP (Narrow .150 Inch)
(Reference 05-08-1641)
0.386 0.393* (9.804 9.982) 0.004 0.009 (0.102 0.249) 1615 0.033 (0.838)
0.0250 (0.635)
0.229 0.244 (5.817 6.198)
0.150 0.157** (3.810 3.988)
GN28 (SSOP) 1098
www.linear.com
LINEAR TECHNOLOGY CORPORATION 1999
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