ILABLE EVALUATIO Simple Current-Limited Switch-Mode Charger Contr

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ILABLE EVALUATIO Simple Current-Limited Switch-Mode Charger Contr

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19-2099; 7/01
ILABLE EVALUATIO
Simple Current-Limited Switch-Mode Charger Controller
low-cost MAX1873R/S/T provides functions needed simply efficiently charge 4series lithium-ion cells more. provides regulated charging current voltage with less than ±0.75% total voltage error battery terminals. external P-channel MOSFET operates step-down DC-DC configuration efficiently charge batteries low-cost designs. MAX1873R/S/T regulates battery voltage charging current using control loops that work together transition smoothly between voltage current regulation. additional control loop limits current drawn from input source that adapter size cost minimized. analog voltage output proportional charging current also supplied that microcontroller monitor charging current. MAX1873 also used efficient currentlimited source charge NiCd NiMH batteries multichemistry charger designs. MAX1873R/S/T available space-saving 16-pin QSOP package. evaluation (MAX1873EVKIT) help reduce design time. Low-Cost Simple Circuit Charges 4-Series Lithium-Ion Cells Adapter Input-Current-Limit Loop Also Charges Ni-Based Batteries Analog Output Monitors Charge Current ±0.75% Battery-Regulation Voltage Shutdown Battery Current Input Voltage 200mV Dropout Voltage/100% Duty Cycle Adjustable Charging Current 300kHz Oscillator Reduces Noise Space-Saving 16-Pin QSOP MAX1873 Evaluation Available Speed Designs
Features
MAX1873
Ordering Information
PART MAX1873REEE MAX1873SEEE MAX1873TEEE TEMP. RANGE -40°C +85°C -40°C +85°C -40°C +85°C PIN-PACKAGE QSOP QSOP QSOP
Applications
Notebook Computers Portable Internet Tablets 4-cell Battery Pack Chargers 10-cell Battery Pack Chargers Hand-Held Instruments Portable Desktop Assistants (PDAs) Desktop Cradle Chargers
Typical Operating Circuit
2CELLS) CSSP SYSTEM LOAD
Selector Guide
PART MAX1873REEE MAX1873SEEE MAX1873TEEE SERIES CELLS CHARGE 2-Cell 6-cell Battery 3-Cell 9-cell Battery 4-Cell 10-cell Battery Packs
200mV
DCIN
MAX1873
CSSN
IOUT ICHG/EN BATT VADJ
Configuration appears data sheet.
4-CELL
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim/Dallas Direct! 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
Simple Current-Limited Switch-Mode Charger Controller MAX1873
ABSOLUTE MAXIMUM RATINGS
CSSP, CSSN, DCIN .-0.3V +30V ICHG/EN GND.-0.3V DCIN.-6V +0.3V .(VDCIN 0.3V) -0.3V .+6V -0.3V DCIN VL.+30V -0.3V VADJ, REF, CCI, CCV, CCS, IOUT GND.-0.3V 0.3V) BATT, GND.-0.3V +20V CSSP CSSN.-0.3V +0.6V BATT.-0.3V +0.6V Source Current .+50mA Sink Current .+40mA Continuous Power Dissipation +70°C) 16-Pin QSOP (derate 8.3mW/°C above +70°C.+667mW Operating Temperature Range MAX1873_EEE .-40°C +85°C Junction Temperature +150°C Storage Temperature Range .-65°C +150°C Lead Temperature (soldering, 10s) +300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuit Figure VDCIN VCSSP VCSSN 18V, VICHG/EN VREF, VVADJ VREF/2. MAX1873R: VBATT VCSB 8.4V; MAX1873S: VBATT VCSB 12.6V; MAX1873T: VBATT VCSB 16.8V; +85°C. Typical values +25°C, unless otherwise noted.)
PARAMETER INPUT SUPPLY REFERENCE DCIN Input Voltage Range DCIN Quiescent Supply Current DCIN BATT Undervoltage Threshold DCIN BATT Undervoltage Threshold Output Voltage Output Load Regulation Output Voltage Line Regulation Load Regulation SWITCHING REGULATOR Oscillator Frequency Driver Source On-Resistance Driver Sink On-Resistance Output Voltage CSSN/CSSP Input Current CSSN/CSSP Off-State Leakage BATT, Input Current BATT, Input Current DCIN VDCIN <28V, 20mA VCSSN/VCSSP 28V, VDCIN VDCIN VSSN/VCSSP 18V, VBATT VCSB ICHG/EN (charger disabled) ICHG/EN (charger enabled) DCIN BATT (input power removed) 4.75 5.75 6.0V VDCIN DCIN BATT CSSP DCIN, input falling CSSP DCIN, input rising 6.0V VDCIN IREF 21µA (200k load) 6.0V VDCIN IREF 4.179 0.05 0.22 5.15 5.40 4.20 0.175 0.38 5.65 4.221 ppm/V CONDITIONS UNITS
Simple Current-Limited Switch-Mode Charger Controller
ELECTRICAL CHARACTERISTICS (continued)
(Circuit Figure VDCIN VCSSP VCSSN 18V, VICHG/EN VREF, VVADJ VREF/2. MAX1873R: VBATT VCSB 8.4V; MAX1873S: VBATT VCSB 12.6V; MAX1873T: VBATT VCSB 16.8V; +85°C. Typical values +25°C, unless otherwise noted.)
PARAMETER BATT Overvoltage Cutoff Threshold CONDITIONS 2-cell version MAX1873R 3-cell version MAX1873S 4-cell version MAX1873T (Note MAX1873R cells) VVADJ VVADJ VREF/2 VVADJ VREF (Note Battery Regulation Voltage MAX1873S cells) VVADJ VVADJ VREF/2 VVADJ VREF (Note MAX1873T cells) VVADJ VVADJ VREF/2 VVADJ VREF (Note MAX1873R BATT Undervoltage Threshold CURRENT SENSE BATT Battery Current-Sense Voltage BATT Current-Sense Voltage when VBATT 2.5V Cell CSSP CSSN Current-Sense Voltage CONTROL INPUTS/OUTPUTS ICHG/EN Input Threshold ICHG/EN Input Voltage Range Charge Current Adjustment VADJ Input Current ICHG/EN Input Current VADJ Input Voltage Range Full scale scale Trickle charge charge current VCSB VBATT 200mV, IOUT 500µA VCSB VBATT 50mV, IOUT 500µA VCSB VBATT 10mV VCSB VBATT IIOUT sinking 20µA Includes 50mV hysteresis VVADJ VREF/2 VICHG/EN VREF -100 -100 VREF VREF VCSSP VICHG/EN VREF VICHG/EN VREF/4 ICHG/20 trickle charge MAX1873S MAX1873T 10.45 15.675 17.575 7.898 8.337 8.775 11.847 12.505 13.163 15.796 16.674 17.551 16.5 18.5 7.958 8.842 11.937 12.6 13.263 15.916 16.8 17.684 11.55 17.325 19.425 8.018 8.463 8.909 12.027 12.695 13.363 16.036 16.926 17.817 10.4 UNITS
MAX1873
IOUT Voltage
Simple Current-Limited Switch-Mode Charger Controller MAX1873
ELECTRICAL CHARACTERISTICS
(Circuit Figure VDCIN VCSSP VCSSN 18V, VICHG/EN VREF, VVADJ VREF/2. MAX1873R: VBATT VCSB 8.4V; MAX1873S: VBATT VCSB 12.6V; MAX1873T: VBATT VCSB 16.8V; -40°C +85°C. Typical values +25°C, unless otherwise noted.)
PARAMETER INPUT SUPPLY REFERENCE DCIN Input Voltage Range DCIN Quiescent Supply Current DCIN BATT Undervoltage Threshold DCIN BATT Undervoltage Threshold Output Voltage Output Load Regulation Output Voltage Line Regulation Load Regulation SWITCHING REGULATOR Oscillator Frequency Driver Source On-Resistance Driver Sink On-Resistance Output Voltage CSSN/CSSP Input Current CSSN/CSSP Off-State Leakage BATT, Input Current BATT, Input Current BATT Overvoltage Cutoff Threshold DCIN VDCIN <28V, 20mA VCSSN/VCSSP 28V, VDCIN VDCIN VSSN/VCSSP VBATT VCSB ICHG/EN (charger disabled) ICHG/EN (charger enabled) DCIN BATT (input power removed) 2-cell version MAX1873R 3-cell version MAX1873S 4-cell version MAX1873T (Note MAX1873R cells) VVADJ VVADJ VREF/2 VVADJ VREF (Note Battery Regulation Voltage MAX1873S cells) VVADJ VVADJ VREF/2 VVADJ VREF (Note MAX1873T cells) VVADJ VVADJ VREF/2 VVADJ VREF (Note 10.45 15.675 17.575 7.898 8.337 8.775 11.847 12.505 13.163 15.796 16.674 17.551 4.75 5.75 11.55 17.325 19.425 8.018 8.463 8.909 12.027 12.695 13.363 16.036 16.926 17.817 6.0V VDCIN DCIN BATT CSSP DCIN, input falling CSSP DCIN, input rising 6.0V VDCIN IREF 21µA (200k load) 6.0V VDCIN IREF 4.179 0.05 0.22 5.15 0.38 5.65 4.221 ppm/V CONDITIONS UNITS
Simple Current-Limited Switch-Mode Charger Controller
ELECTRICAL CHARACTERISTICS (continued)
(Circuit Figure VDCIN VCSSP VCSSN 18V, VICHG/EN VREF, VVADJ VREF/2. MAX1873R: VBATT VCSB 8.4V; MAX1873S: VBATT VCSB 12.6V; MAX1873T: VBATT VCSB 16.8V; -40°C +85°C. Typical values +25°C, unless otherwise noted.)
PARAMETER BATT Undervoltage Threshold CURRENT SENSE BATT Battery Current-Sense Voltage BATT Current-Sense Voltage when VBATT 2.5V Cell CSSP CSSN Current-Sense Voltage CONTROL INPUTS/OUTPUTS ICHG/EN Input Threshold ICHG/EN Input Voltage Range Charge Current Adjustment VADJ Input Current ICHG/EN Input Current VADJ Input Voltage Range Full scale scale Trickle charge charge current VCSB VBATT 200mV, IOUT 500µA VCSB VBATT 50mV, IOUT 500µA VCSB VBATT 10mV VCSB VBATT IIOUT sinking 20µA VVADJ VREF/2 VICHG/EN VREF Includes 50mV hysteresis -100 -100 VREF VREF VCSSP VICHG/EN VREF VICHG/EN VREF/4 CONDITIONS MAX1873R ICHG/20 trickle charge MAX1873S MAX1873T 10.4 UNITS
MAX1873
IOUT Voltage
Note While appear possible Battery Regulation Voltage higher than Battery Overvoltage Cutoff Threshold, this cannot happen because both parameters derived from same reference track each other. Note Specifications -40°C guaranteed design, production tested.
Simple Current-Limited Switch-Mode Charger Controller MAX1873
Typical Operating Characteristics
(Circuit Figure VDCIN VCSSP VCSSN 18V, VICHG/EN VREF, VVADJ VREF/2. MAX1873R: VBATT VCSB 8.4V; MAX1873S: VBATT VCSB 12.6V; MAX1873T: VBATT VCSB 16.8V; +25°C, unless otherwise noted).
MAX1873T (4-CELL) BATTERY VOLTAGE CHARGING CURRENT
MAX1873 toc01
IOUT VOLTAGE CSB-BATT VOLTAGE
IOUT VOLTAGE
MAX1873 toc02
17.5 15.0 BATTERY VOLTAGE 12.5 10.0 RCSB 0.068
CHARGING CURRENT
CSB-BATT VOLTAGE (mV)
MAX1873T (4-CELL) BATTERY REGULATION VOLTAGE VADJ VOLTAGE
MAX1873 toc03
RECENT VOLTAGE TEMPERATURE
MAX1873 toc04
18.0 BATTERY REGULATION VOLTAGE
4.210 4.205
REFERENCE VOLTAGE
17.5
4.200 4.195 4.190 4.185 MAX1873T 4.180
17.0
16.5
16.0
15.5 VADJ VOLTAGE
TEMPERATURE (°C)
RECENT VOLTAGE
REFERENCE CURRENT
MAX1873 toc05
MAX1873R (2-CELL) EFFICIENCY INPUT VOLTAGE
MAX1873 toc06
4.210 4.205 REFERENCE VOLTAGE 4.200 4.195 4.190 4.185 MAX1873T 4.180
EFFICIENCY
VBATT ICHG REFERENCE VOLTAGE (mA) INPUT VOLTAGE
Simple Current-Limited Switch-Mode Charger Controller
Typical Operating Characteristics (continued)
(Circuit Figure VDCIN VCSSP VCSSN 18V, VICHG/EN VREF, VVADJ VREF/2. MAX1873R: VBATT VCSB 8.4V; MAX1873S: VBATT VCSB 12.6V; MAX1873T: VBATT VCSB 16.8V; +25°C, unless otherwise noted).
MAX1873S (3-CELL) EFFICIENCY INPUT VOLTAGE
MAX1873 toc07
MAX1873
MAX1873T (4-CELL) EFFICIENCY INPUT VOLTAGE
MAX1873 toc08
EFFICIENCY
EFFICIENCY
VBATT 10.5V ICHG INPUT VOLTAGE
VBATT ICHG
INPUT VOLTAGE
4-CELL BATTERY VOLTAGE CHARGING CURRENT TIME
MAX1873 toc09
CHARGING CURRENT SYSTEM LOAD CURRENT
MAX1873 toc10
BATTERY VOLTAGE CHARGING CURRENT BATTERY VOLTAGE
CHARGING CURRENT CHARGING CURRENT
TIME (MINUTES)
SYSTEM LOAD CURRENT
Simple Current-Limited Switch-Mode Charger Controller MAX1873
Description
NAME CSSN CSSP FUNCTION Source Current-Sense Negative Input. Connect current-sense resistor between CSSP CSSN limit total current drawn from input source. disable input current sensing, connect CSSN CSSP. Source Current-Sense Positive Input. Also used input source undervoltage sensing. Input-Source-Current Regulation Loop Compensation Point Battery Regulation Voltage Control-Loop Compensation Point. Pulling high through 1.5k resistor disables voltage control loop charging NiCd NiMH batteries. Battery Charge Current Control-Loop Compensation Point Battery Charging Current Adjust/Shutdown Input. This connected resistive-divider between adjust charge current sense threshold between BATT. When ICHG/EN connected REF, CSB-BATT threshold 200mV. Pull ICHG/EN (below 500mV) disable charging reduce supply current 5µA. Charge Current Monitor Output. Analog Voltage Output that proportional charging current. VIOUT (VCSB VBATT) 200mV current-sense voltage (maximum load capacitance 5nF). Battery Regulation Voltage Adjust. battery regulation voltage from 3.979V cell 4.421V cell with resistors. Output accuracy remains better than 0.75% even with adjusting resistors reduced adjustment range. 4.2V, voltage-divider resistors must equal value (nominally 100k each). 4.2V Reference Voltage Output. Bypass with ceramic capacitor. Battery Voltage-Sense Input Battery Current-Sense Negative Input. Bypass with 68µF MAX1873R, 47µF MAX1873S, 33µF MAX1873T. capacitors with Battery Current-Sense Positive Input Ground Internal Regulator. internally supplies power driver. Connect 0.22µF ceramic capacitor between DCIN. Drive Output External PFET. swings from VDCIN VDCIN Power-Supply Input. DCIN input supply charger Bypass with 0.22µF ceramic capacitor. Internal Regulator. powers MAX1873's control logic 5.4V. Bypass with 2.2µF larger ceramic capacitor.
ICHG/EN
IOUT
VADJ
BATT DCIN
Simple Current-Limited Switch-Mode Charger Controller MAX1873
MBR5340 CELLS) 2.2µF 0.22µF DCIN CSSN CSSP 0.01µF 0.01µF
CDCIN 0.22µF
RCSS 0.033 SYSTEM LOAD MBR5340 47µF
MAX1873
200mV RCSB 47nF IOUT ICHG/EN CCCS 47nF CCCVS 0.1µF RCCV VADJ BATT
100k DISABLE
10µH
RCSB 0.068
CBATT 68µF
CREF
BATTERY 4-CELLS)
CCCVP
Figure Typical Application Circuit
Detailed Description
MAX1873 includes functions necessary charge 4-series cell lithium-ion (Li+) battery packs. includes high-efficiency step-down DC-DC converter that controls charging voltage current. also features input source current limiting that adapter that supplies less than total system current addition charging current used without fear overload. DC-DC converter uses external P-channel MOSFET switch, inductor, diode convert input voltage charging current charging voltage. typical application circuit shown Figure Charging current RCSB, while battery voltage measured BATT. battery regulation voltage limit nominally 8.4V version (2-cells), 12.6V version (3-cells), 16.8V version (4-cells),
also adjusted other voltages different chemistries.
Voltage Regulator
batteries require high-accuracy voltage limit while charging. battery regulation voltage nominally 4.2V cell adjusted ±5.25% setting voltage VADJ between ground. limiting adjust range regulation voltage, overall voltage accuracy better than ±0.75% maintained while using resistors. internal error amplifier maintains voltage regulation within ±0.75%. amplifier compensated (see Figure Individual compensation voltage regulation current regulation loops allows optimal compensation each. typical compensation network shown Figure will suffice most designs.
Simple Current-Limited Switch-Mode Charger Controller
CSSN REGULATOR UNDERVOLTAGE COMPARATOR BATT DCIN DRIVER CONTROL LOGIC ICHG CURRENT ERROR IOUT BATT
CSSP
SHUTDOWN BLOCKS
VOLTAGE ERROR
portions system powered sleep. Without benefit input-current regulation, input source would have able supply maximum system current plus maximum charger-input current. MAX1873 input-current loop ensures that system always gets adequate power reducing charging current needed. using input-current limiter, size cost adapter reduced. Setting Input-Current Limit section design details. Input current measured through external sense resistor, RCSS, between CSSP CSSN. inputcurrent limit feature bypassed connecting CSSP CSSN. input-current error amplifier compensated CCS. 47nF capacitor from provides suitable performance most applications.
MAX1873
Controller
pulse-width modulation (PWM) controller drives external MOSFET constant 300kHz regulate charging current voltage while maintaining noise. controller accepts inputs from CCI, CCV, error amplifiers. lowest signal these three drives controller. internal clamp limits noncontrolling signals within 200mV controlling signal prevent delay when switching between battery-voltage control, charging-current control, input-current regulation loops.
VADJ
4.2V REFERENCE
Shutdown
MAX1873 stops charging when ICHG/EN pulled (below 0.5V) shuts down when voltage DCIN falls below voltage BATT. shutdown, internal resistive voltage-divider disconnected from BATT reduce battery drain. When AC-adapter power removed, when part shut down, MAX1873 typically draws 1.5µA from battery.
Figure Functional Block Diagram
Charging-Current Regulator
charging-current regulator limits battery charging current. Current sensed current-sense resistor (RCSB Figure connected between BATT CSB. voltage ICHG/EN also adjust charging current. Full-scale charging current (ICHG 0.2V RCSB) achieved connecting ICHG/EN REF. Setting Charging-Current Limit section more details. charging-current error amplifier compensated (Figure 47nF capacitor from provides suitable performance most applications.
Source Undervoltage Shutdown (Dropout)
DCIN voltage compared voltage BATT. When voltage DCIN drops below BATT 50mV, charger turns off, preventing drain battery when input source present below battery voltage. diode typically connected between input source charger input. This diode prevents battery from discharging through body diode high-side MOSFET should input shorted GND. also protects charger, battery, systems from reversed polarity adapters negative input voltages.
Input-Current Regulator
input-current regulator limits source current reducing charging current when input current reaches input-current limit. typical portable design, system load current will normally fluctuate
Simple Current-Limited Switch-Mode Charger Controller
Charge-Current Monitor Output
IOUT analog voltage output that proportional actual charge current. With microcontroller, IOUT signal facilitate gas-gauging, indicate percent charge, charge-time remaining. equation governing this output VIOUT VCSB VBATT VOUT 20(RCSB ICHG where VCSB VBATT voltages BATT pins, ICHG charging current. IOUT drive load capacitance 5nF.
Setting Charging-Current Limit
charging current ICHG sensed currentsense resistor RCSB between BATT, also adjusted voltage ICHG/EN. ICHG/EN connected (the standard connection), charge current given ICHG 0.2V RCSB some cases, common values RCSB allow desired charge-current value. also desirable reduce 0.2V CSB-to-BATT sense threshold reduce power dissipation. such cases, ICHG/EN input used reduce charge-current-sense threshold. those cases equation charge current becomes: ICHG 0.2V VICH VREF RCSB
MAX1873
Design Procedure
Setting Battery-Regulation Voltage
batteries, VADJ sets per-cell battery-regulation voltage limit. VADJ voltage, resistive-divider from (Figure battery voltage 4.2V cell, resistors equal value (100k each) VADJ voltage-divider. other battery-regulation voltages, remainder this section. per-cell battery regulation voltage function battery chemistry construction usually clearly specified manufacturer. this clearly specified, sure consult battery manufacturer determine this voltage before charging battery. Once per-cell voltage determined, VADJ voltage calculated equation: VVADJ 9.5( VBATTR (9VREF where VBATTR desired battery-regulation voltage (for total series-cell stack), number battery cells, VREF reference voltage (4.2V). VVADJ choosing should selected that total divider resistance (R1+ near 200k. then calculated follows: VVADJ VREF VVADJ Since full range VADJ (from VREF) results ±5.263% adjustment battery-regulation limit (3.979V 4.421V), resistive-divider's accuracy need tight output-voltage accuracy. Using resistors voltage-divider still provides ±0.75% battery-voltage-regulation accuracy.
Setting Input-Current Limit
input-source current limit, IIN, inputcurrent sense resistor, (Figure connected between CSSP CSSN. equation source current 0.1V RCSS This limit typically current rating input power source adapter protect input source from overload. Short CSSP CSSN DCIN input-source current-limit feature used.
Inductor Selection
inductor value selected more less ripple current. greater inductance, lower ripple current. However, physical size kept same, larger inductance value typically results higher inductor series resistance lower inductor saturation current. Typically, good tradeoff choose inductor such that ripple current approximately average charging current. ratio ripple current charging current (LIR) used calculate inductor value: VBATT VDCIN(MAX) VBATT
[VDCIN(MAX) ICHG LIR]
where switching frequency (nominally 300kHz) ICHG charging current. peak inductor current given
Simple Current-Limited Switch-Mode Charger Controller MAX1873
IPEAK ICHG example, 4-cell charging current VDCIN(MAX) 24V, 0.5, calculated 11.2µH with peak current 3.75A. Therefore 10µH inductor would satisfactory. PTOT
Diode Selection
Schottky rectifier with current rating least charge current limit must connected from MOSFET drain GND. voltage rating diode must exceed maximum expected input voltage.
MOSFET Selection
MAX1873 uses P-channel power MOSFET switch. MOSFET must selected meet efficiency power dissipation requirements charging circuit well maximum temperature MOSFET. Characteristics that affect MOSFET power dissipation drain-source on-resistance (RDS(ON)) gate charge. Generally these inversely proportional. determine MOSFET power dissipation, operating duty cycle must first calculated. When charger operating higher currents, inductor current will continuous (the inductor current will drop this case, high-side MOSFET duty cycle approximated equation: BATT VDCIN catch-diode duty cycle (D') will VBATT DCIN VDCIN where VBATT battery-regulation voltage (typically 4.2V cell) VDCIN source-input voltage. MOSFETs, worst-case power dissipation on-resistance (PR) occurs maximum duty cycle, where operating conditions minimum sourcevoltage maximum battery voltage. approximated equation: VBATT(MAX) VDCIN(MIN) RDS(ON) ICHG2
Capacitor Selection
input capacitor shunts switching current from charger input prevents that current from circulating through source, typically wall cube. Thus input capacitor must able handle input current. high charging currents, converter will typically operate continuous conduction. this case, current input capacitor approximated with equation: ICIN ICHG where ICIN input capacitor current, converter duty cycle (typically VBATT/VDCIN), ICHG battery-charging current. maximum input current occurs duty cycle, worst-case input-ripple current ICHG. input-to-output voltage ratio such that controller will never work duty cycle, then worst-case capacitor current will occur where duty cycle nearest 50%. impedance input capacitor critical preventing currents from flowing back into wall cube. This requirement varies depending wall cube's impedance requirements conducted radiated specifications that must met. aluminum electrolytic capacitors used, however, tantalum high-value ceramic capacitors generally provide better performance. output filter capacitor absorbs inductor-ripple current. output-capacitor impedance must significantly less than that battery ensure that will absorb ripple current. Both capacitance rating capacitor important effectiveness filter ensure stability circuit. minimum output capacitance stability VBATT VREF VDCIN(MIN) COUT VBATT RCSB
Transition losses approximated equation: DCIN where MOSFET transition time switching frequency. total power dissipation MOSFET then:
Simple Current-Limited Switch-Mode Charger Controller
where COUT total output capacitance, VREF reference voltage (4.2V), VBATT maximum battery regulation voltage (typically 4.2V cell), VDCIN (MIN) minimum source-input voltage, RCSB current-sense resistor (68m charging current) from BATT. maximum output capacitor allowed stability RESR BATT VREF where RESR output capacitor ESR. tings interfere with charging. However, battery undervoltage-protection features remain active charging current reduced when VBATT less than levels stated BATT Undervoltage Threshold line Electrical Characteristics Table. 6-series cells charged with version device, 9-cells with version, 10-cells with version. MAX1873 contains charge-termination algorithms cells; acts only current source. separate microcontroller Ni-cell charge controller must instruct MAX1873 terminate charging.
MAX1873
Compensation Components
three regulation loops: input current limit, charging current limit, charging voltage limit compensated separately using CCS, CCI, pins, respectively. charge-current loop error-amplifier output brought CCI. Likewise, source-current erroramplifier output brought CCS. 47nF capacitors ground compensate current loops most charger designs. Raising value these capacitors reduces bandwidth these loops. voltage-regulating loop error-amplifier output brought CCV. Compensate this loop connecting capacitor parallel with series resistor-capacitor from GND. Recommended values shown Figure PROCESS: BiCMOS TRANSISTOR COUNT: 1397
Chip Information
Applications Information
Bypassing
MAX1873 uses internal linear regulators power internal circuitry. outputs linear regulators powers internal control circuitry while powers MOSFET gate driver. also power limited amount external circuitry, long maximum current (3mA) exceeded. 2.2µF bypass capacitor required from ensure stability. 0.22µF capacitor required from DCIN. bypass capacitor required between ensure that internal 4.2V reference stable. cases, low-ESR ceramic capacitors.
VIEW
CSSN CSSP ICHG/EN IOUT VADJ DCIN
Configuration
MAX1873R/S/T
BATT
Charging NiMH NiCd Cells
MAX1873 used multichemistry chargers. When charging NiMH NiCd cells, pull high with resistor. This disables voltage control loop battery-regulation voltage set-
QSOP
Simple Current-Limited Switch-Mode Charger Controller MAX1873
Package Information
QSOP.EPS
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2001 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.

ILABLE EVALUATIO Simple Current-Limited Switch-Mode Charger Contr

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