MAX8731ETI+ Fast Delivery |IC PHOENIX CO.,LIMITED

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MAX8731ETI+
SMBus Level 2 Battery Charger with Remote Sense
General Description
The MAX8731 is an SMBus™ programmable multichem-
istry battery charger. The MAX8731 uses a minimal
command set to easily program the charge voltage,
charge current, and adapter current limit.
The MAX8731 charges one to four Li+ series cells and
delivers up to 8A charge current. The MAX8731 drives
n-channel MOSFETs for improved efficiency and
reduced cost. Low-offset current-sense amplifiers pro-
vide high accuracy with 10mΩsense resistors.
The MAX8731 current-sense amplifiers provide high
accuracy (3% at 3.5A) and also provide fast cycle-by-
cycle current-mode control to protect against battery
short circuit and system load transients.
The charger employs dual remote-sense, which reduces
charge time by measuring the feedback voltage directly
at the battery, improving accuracy of initial transition into
constant-voltage mode. The MAX8731 provides 0.5%
battery voltage accuracy directly at the battery terminal.
The MAX8731 provides a digital output that indicates the
presence of the AC adapter, as well as an analog output
that indicates the adapter current within 4% accuracy.
The MAX8731 is available in a small 5mm x 5mm,
28-pin, thin (0.8mm) QFN package. An evaluation kit is
available to reduce design time. The MAX8731 is avail-
able in lead-free packages.
Applications
Notebook Computers
Tablet PCs
Medical Devices
Portable Equipment with Rechargeable Batteries
Features0.5% Battery Voltage Accuracy 3% Input Current-Limit Accuracy3% Charge-Current AccuracySMBus 2-Wire Serial InterfaceCycle-by-Cycle Current Limit
Battery Short-Circuit Protection
Fast Response for Pulse Charging
Fast System-Load-Transient ResponseDual-Remote-Sense InputsMonitor Outputs for
Adapter Current (4% Accuracy)
AC Adapter Detection11-Bit Battery Voltage Setting6-Bit Charge-Current/Input-Current Setting8A (max) Battery Charger Current11A (max) Input Current+8V to +26V Input Voltage RangeCharges Li+, NiMH, and NiCd Battery Chemistries
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
Ordering Information
Typical Operating Circuit
19-3923; Rev 0; 1/06
SMBus is a trademark of Intel Corp.+Indicates lead-free packaging.
PARTTEMP RANGEPIN-PACKAGE
MAX8731ETI+-40°C to +85°C28 Thin QFN (5mm x 5mm)
EVALUATION KIT
AVAILABLE
EXTERNAL
LOAD
DCIN
GND
REF
ACIN
BATSEL
BATTERY
BATTERY
SCL
SDA
VDD
GND
ACOK
VCC
LDO
FBSB
FBSA
BST
PGND
CSIN
CSIP
DLO
DHI
OPTIONAL
IINPCCV
DACCCS
CSSPCSSN
SELECTORBATSEL
CCI
HOST
SCL
SDA
VDDMAX8731
MAX8731
THIN QFN5mm x 5mm
TOP VIEW
ACIN
CCS
CCI
CCVDAC
GND
DLOCSIPCSINLDOFBSBFBSA
BST672119171615
VCC
CSSN
GND
VDD
SCL
SDA
REF
PGND8CSSPIINP
*EXPOSED PADDLE
DHI13ACOKLX14BATSELDCIN
Pin Configuration
SMBus Level 2 Battery Charger with
Remote Sense
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDCIN= VLX= VCSSP= VCSSN= 19V, VBST- VLX= 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF, VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
DCIN, CSSN, CSIN, FBSA, FBSB to GND..............-0.3V to +28V
CSSP to CSSN, CSIP to CSIN, PGND to GND......-0.3V to +0.3V
BST to GND............................................................-0.3V to +32V
BST to LX..................................................................-0.3V to +6V
DHI to LX.................................................-0.3V to +(VBST+ 0.3)V
DLO to PGND..........................................-0.3V to +(LDO + 0.3)V
LX to GND.................................................................-6V to +28V
CCI, CCS, CCV, DAC, REF,
IINP to GND...........................................-0.3V to (VVCC+ 0.3)V
VDD, SCL, SDA, BATSEL, ACIN, ACOK, VCCto GND,
LDO to PGND......................................................-0.3V to +6V
Continuous Power Dissipation (TA= +70°C)
28-Pin Thin QFN
(derate 20.8mW/°C above +70°C)........................1666.7 mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-60°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERCONDITIONS MIN TYP MAX UNITSCHARGE-VOLTAGE REGULATION16.716 16.8 16.884 V ChargingVoltage() = 0x41A0 -0.5 +0.5 %12.491 12.592 12.693 V ChargingVoltage() = 0x3130 -0.8 +0.8 %8.333 8.4 8.467 V ChargingVoltage() = 0x20D0 -0.8 +0.8 %4.15 4.192 4.234 VBattery Full-Charge Voltage and
AccuracyChargingVoltage() = 0x1060 -1.0 +1.0 %Battery Undervoltage-Lockout
Trip Point for Trickle Charge 2.5 VCHARGE-CURRENT REGULATIONCSIP to CSIN Full-Scale Current-
Sense Voltage 78.22 80.64 83.06 mV7.822 8.064 8.306 A RS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x1f80 -3 +3 %3.809 3.968 4.126 A RS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x0f80 -4 +4 % Charge Current and AccuracyRS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x0080 (128mA) 64 400 mACharge-Current Gain Error Based on ChargeCurrent() = 128mA and 8.064A -2 +2 %FBSA/FBSB/CSIP/CSIN
Input Voltage Range 0 19 V
MAX8731
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN= VLX= VCSSP= VCSSN= 19V, VBST- VLX= 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF, VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERCONDITIONS MIN TYP MAX UNITSAdapter present, not charging, ICSIP + ICSIN + ILX + IFBS,
VFBS_ = VLX = VCSIN = VCSIP = 19V 2 5Battery Quiescent Current Ad ap ter ab sent, IC S I P + IC S I N + ILX + IFBS A + IFBS B + IC S S P IC S S N , V FBS _ = V LX = V C S I N = V C S I P = 19V , V D C I N = 0V +1µAVAdapter = 26V, VBattery = 16.8V, not
charging 200 500 µACharging 0.4 1 mA VAdapter = 19V,
VBattery = 16.8V Not charging 200 500 µACharging 0.4 1 mAAdapter Quiescent Current IDCIN +
ICSSP +
ICSSN VAdapter = 8V,
VBattery = 4V Not charging 200 500 µAINPUT-CURRENT REGULATIONCSSP to CSSN Full-Scale
Current-Sense Voltage VFBS_ = 19V 106.7 110 113.3 mVRS1 (Figure 1) = 10mΩ, InputCurrent() = 11004mA or
3584mA -3 +3 % Input Current AccuracyRS1 (Figure 1) = 10mΩ, InputCurrent() = 2048mA -5 +5 %POR Input Current RS1 (Figure 1) = 10mΩ 256 mAInput Current-Limit Gain Error -2 +2 %Input Current-Limit Offset Based on InputCurrent() = 1024mA and 11004mA -1 +1 mVCSSP/CSSN Input Voltage Range 8 26 VIINP Transconductance VCSSP - CSSN = 110mV 2.85 3.0 3.15 mA/VIINP Offset Based on VCSSP - CSSN = 110mV and 20mV -1.5 +1.5 mVVCSSP - CSSN = 110mV -5 +5VCSSP - CSSN = 55mV or 35mV -4 +4 IINP AccuracyVCSSP - CSSN = 20mV -10 +10%IINP Output Voltage Range 0 3.5 VSUPPLY AND LINEAR REGULATORDCIN, Input Voltage Range 8.0 26.0 VDCIN falling 7 7.4 DCIN Undervoltage-Lockout
Trip Point DCIN rising 7.5 7.85 VVCSSP - VCSIN falling 9 15 21 Power-Fail Threshold VCSSP - VCSIN rising 160 210 271 mV
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN= VLX= VCSSP= VCSSN= 19V, VBST- VLX= 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF, VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
PARAMETERCONDITIONS MIN TYP MAX UNITSLDO Output Voltage 8.0V < VDCIN < 28V, no load 5.25 5.4 5.55 VLDO Load Regulation 0 < ILDO < 30mA 34 100 mVLDO Undervoltage-Lockout Threshold VDCIN = 8.0V, VLDO falling 3.20 4 5.15 VVDD Range 2.7 5.5 VVDD UVLO Rising 2.5 2.7 VVDD UVLO Hysteresis 100 mVVDD Quiescent Current DCIN < 6V, VDD = 5.5V, SCL = SDA = 5.5V 16 27 µAREFERENCE REF Output Voltage 0 < IREF < 500µA 4.071 4.096 4.120 VREF Undervoltage-Lockout Trip Point REF falling 3.1 3.9 VACOK ACOK Sink Current VACOK = 0.4V, ACIN = 1.5V 1 mAACOK Leakage Current VACOK = 5.5V, ACIN = 2.5V 1 µAACIN ACIN Threshold 2.007 2.048 2.089 VACIN Threshold Hysteresis 10 20 30 mVACIN Input Bias Current -1 +1 µAREMOTE-SENSE INPUTS FBS_ Range VCSIN - VFBS 0 200 mVFBS_ Gain ∆VCSIN / ∆(VCSIN - VFBS_) 0.95 1.00 1.05 V/VCSIN-FBS_ Clamp Voltage 225 250 275 mVFBS_ Bias Current Charger switching, FBS_ selected 14 µAFBS_ Bias Current Charger not switching or FBS_ not selected -2 +2 µASWITCHING REGULATORVCSIN = 16.0V, VCSSP = 19V 360 400 440 Off-Time VCSIN = 16.0V, VCSSP = 17V 260 300 360 nsBST Supply Current DHI high 500 800 µALX Input Bias Current VDCIN = 28V, VCSIN = VLX = 20V, DHI low 2 µAMaximum Discontinuous-Mode Peak
Current (IMIN) 0.5 ADHI On-Resistance Low IDHI = -10mA 1 3 ΩDHI On-Resistance High IDHI = 10mA 3 5 ΩDLO On-Resistance High IDLO = 10mA 3 5 ΩDLO On-Resistance Low IDLO = -10mA 1 3 Ω
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN= VLX= VCSSP= VCSSN= 19V, VBST- VLX= 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF, VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
PARAMETERCONDITIONS MIN TYP MAX UNITSERROR AMPLIFIERSGMV Amplifier Transconductance C har g i ng V ol tag e( ) = 16.8V , V FBS_ = 16.8V 0.0625 0.125 0.2500 mA/VGMI Amplifier Transconductance ChargingCurrent() = 3968mA, VCSIP - VCSIN = 39.68mV 0.5 1 2.0 mA/VGMS Amplifier Transconductance InputCurrent() = 3968mA, VCSSP - VCSSN = 79.36mV 0.5 1 2.0 mA/VCCI/CCS/CCV Clamp Voltage 0.25V < VCCI/S/V < 2.0V 120 250 600 mVLOGIC LEVELS
SDA/SCL Input Low VoltageVDD = 2.7V to 5.5V0.8 V
SDA/SCL Input High VoltageVDD = 2.7V to 5.5V2.1 V
SDA/SCL Input Bias CurrentVDD = 2.7V to 5.5V-1+1 µA
BATSEL Input Low Voltage0.8 V
BATSEL Input High Voltage2.1 V
BATSEL Input Bias Current-1+1 µA
SDA, Output Sink CurrentV(SDA) = 0.4V6 mASMBus TIMING SPECIFICATIONS (VDD = 2.7V to 5.5V) (see Figures 4 and 5)
PARAMETERSSYMBOLCONDITIONSMINTYPMAX UNITS
SMBus FrequencyfSMB10100 kHz
Bus Free TimetBUF4.7 µs
Start Condition Hold Time from
SCLtHD:STA4 µs
Start Condition Setup Time from
SCLtSU:STA4.7 µs
Stop Condition Setup Time from
SCLtSU:STO4 µs
SDA Hold Time from SCLtHD:DAT300 ns
SDA Setup Time from SCLtSU:DAT250 ns
SCL Low TimeouttTIMEOUT(Note 1)2535 ms
SCL Low PeriodTLOW4.7 µs
SCL High PeriodTHIGH4 µs
Maximum Charging Period
Without a ChargeVoltage() or
ChargeCurrent() Command
140175210 s
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICSDCIN= VLX= VCSSP= VCSSN= 19V, VBST - VLX = 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF , VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETERCONDITIONS MIN TYP MAX UNITSCHARGE-VOLTAGE REGULATION16.632 16.968 V ChargingVoltage() = 0x41A0 -1 +1 %12.466 12.717 V ChargingVoltage() = 0x3130 -1 +1 %8.316 8.484 V ChargingVoltage() = 0x20D0 -1 +1 %4.129 4.255 VBattery Full-Charge Voltage and
AccuracyChargingVoltage() = 0x1060 -1.5 +1.5 %CHARGE-CURRENT REGULATIONCSIP to CSIN Full-Scale Current-
Sense Voltage 78.22 83.05 mV7.822 8.305 A RS2 (Figure 1) = 10mΩ;
ChargingCurrent()= 0x1f80 -3 +3 %3.809 4.126 A RS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x0f80 -4 +4 % Charge Current and AccuracyRS2 (Figure 1) =10mΩ;
ChargingCurrent() = 0x0080 30 400 mACharge-Current Gain Error Based on ChargeCurrent() = 128mA and 8.064A -2 +2 %FBSA/FBSB/CSIP/CSIN Input
Voltage Range 0 19 VAdapter present, not charging, ICSIP + ICSIN + ILX + IFBS,
VFBS_ = VLX = VCSIN = VCSIP = 19V 5Battery Quiescent Current Adapter absent, ICSIP + ICSIN + ILX + IFBSA + IFBSB +
ICSSP + ICSSN, VFBS_= VLX = VCSIN = VCSIP = 19V,
VDCIN = 0V 1µAV A d a p t er = 26V , V B at te r y = 16.8V , not char g i ng 500 µACharging 1 mA VAdapter = 19V,
VBattery = 16.8V Not charging 500 µACharging 1 mAAdapter Quiescent Current IDCIN +
ICSSP +
ICSSN VAdapter = 8V,
VBattery = 4V Not charging 500 µA
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)DCIN= VLX= VCSSP= VCSSN= 19V, VBST - VLX = 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF , VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETERCONDITIONS MIN TYP MAX UNITSINPUT-CURRENT REGULATIONCSSP to CSSN Full-Scale
Current-Sense Voltage VFBS_ = 19V 103.3 116.6 mVRS1 (Figure 1) = 10mΩ;
InputCurrent() = 11004mA or 3584mA -6 +6Input Current Accuracy RS1 (Figure 1) = 10mΩ;
InputCurrent() = 2048mA -5 +5%Input Current-Limit Gain Error Based on InputCurrent() = 1024mA and 11004mA -5 +5 %Input Current-Limit Offset Based on InputCurrent() = 1024mA and 11004mA -1 +1 mVCSSP/CSSN Input Voltage Range 8 26 VIINP Transconductance VCSSP - CSSN = 110mV 2.7 3.3 mA/VIINP Offset Based on VCSSP - CSSN = 110mV and 20mV -1.5 +1.5 mVVCSSP - CSSN = 110mV -5 +5VCSSP - CSSN = 55mV or 35mV -4 +4 IINP AccuracyVCSSP - CSSN = 20mV -10 +10%IINP Output Voltage Range 0 3.5 VSUPPLY AND LINEAR REGULATORDCIN, Input Voltage Range 8.0 26.0 VDCIN falling 7 DCIN Undervoltage-Lockout
Trip Point DCIN rising 7.85 VVCSSP - VCSIN falling 9 21 POWER_FAIL Threshold VCSSP - VCSIN rising 160 271 mVLDO Output Voltage 8.0V < VDCIN < 28V, no load 5.25 5.55 VLDO Load Regulation 0 < ILDO < 30mA 100 mVLDO Undervoltage-Lockout
Threshold VDCIN = 8.0V, VLDO falling 3.20 5.15 VVDD Range 2.7 5.5 VVDD UVLO Rising 2.7 VVDD Quiescent Current DCIN < 6V, VDD = 5.5V, SCL = SDA = 5.5V 27 µAREFERENCEREF Output Voltage 0 < IREF < 500µA 4.053 4.139 VREF Undervoltage-Lockout
Trip Point REF falling 3.9 VACOK ACOK Sink Current VACOK = 0.4V, ACIN = 1.5V 1 mA
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)DCIN= VLX= VCSSP= VCSSN= 19V, VBST - VLX = 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF , VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1; TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETERCONDITIONS MIN TYP MAX UNITSACINACIN Threshold 2.007 2.089 VACIN Threshold Hysteresis 10 30 mVREMOTE-SENSE INPUTSFBS_ Range VCSIN - VFBS 0 200 mVFBS_ Gain ΔVCSIN / Δ(VCSIN - VFBS_) 0.9 1.1 V/VCSIN-FBS_ Clamp Voltage 220 280 mVFBS_ Bias Current Charger switching, FBS_ selected 14 µASWITCHING REGULATORVCSIN = 16.0V, VCSSP = 19V 360 440 Off-Time VCSIN = 16.0V, VCSSP = 17V 260 350 nsBST Supply Current DHI high 800 µADHI On-Resistance Low IDHI = -10mA 3 ΩDHI On-Resistance High IDHI = 10mA 5 ΩDLO On-Resistance High IDLO = 10mA 5 ΩDLO On-Resistance Low IDLO = -10mA 3 ΩERROR AMPLIFIERSGMV Amplifier Transconductance C har g i ng V ol tag e( ) = 16.8V , V FBS_ = 16.8V 0.0625 0.2500 mA/VGMI Amplifier Transconductance ChargingCurrent() = 3968mA, VCSIP - VCSIN = 39.68mV 0.5 2.0 mA/VGMS Amplifier Transconductance InputCurrent() = 3968mA, VCSSP - VCSSN = 79.36mV 0.5 2.0 mA/VCCI/CCS/CCV Clamp Voltage 0.25V < VCCI/S/V < 2.0V 150 600 mVLOGIC LEVELS
SDA/SCL Input Low VoltageVDD = 2.7V to 5.5V0.8 V
SDA/SCL Input High VoltageVDD = 2.7V to 5.5V2.3 V
BATSEL Input Low Voltage0.8 V
BATSEL Input High Voltage2.3 V
SDA, Output Sink CurrentV(SDA) = 0.4V6 mA
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN= VLX = VCSSP= VCSSN= 19V, VBST - VLX= 4.5V, VFBSA= VFBSB= VCSIP= VCSIN= 16.8V, BATSEL = GND = PGND = 0,
CLDO= 1µF, VCC= LDO, CREF= 1µF, CDAC= 0.1µF , VDD= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated
per Figure 1; TA= -40°C to +85°C, unless otherwise noted.) (Note 2)SMB TIMING SPECIFICATION (VDD = 2.7V to 5.5V) (see Figures 4 and 5)
PARAMETERSSYMBOLCONDITIONSMINTYPMAX UNITS
SMBus FrequencyfSMB10100 kHz
Bus Free TimetBUF4.7 µs
Start Condition Hold Time from
SCLtHD:STA4 µs
Start Condition Setup Time from
SCLtSU:STA4.7 µs
Stop Condition Setup Time from
SCLtSU:STO4 µs
SDA Hold Time from SCLtHD:DAT300 ns
SDA Setup Time from SCLtSU:DAT250 ns
SCL Low TimeouttTIMEOUT(Note 1)2535 ms
SCL Low PeriodTLOW4.7 µs
SCL High PeriodTHIGH4 µs
Maximum Charging Period
Without a ChargeVoltage() or
ChargeCurrent() Command
140210 s
Note 1:Devices participating in a transfer will timeout when any clock low exceeds the 25ms minimum timeout period. Devices that
have detected a timeout condition must reset the communication no later than the 35ms maximum timeout period. Both a
master and a slave must adhere to the maximum value specified as it incorporates the cumulative stretch limit for both a
master (10ms) and a slave (25ms).
Note 2:Specifications to -40°C are guaranteed by design, not production tested.
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
Typical Operating Characteristics
(Circuit of Figure 1, adapter = 19.5V, ChargeVoltage() = 16.8V, ChargeCurrent() = 3.854A, InputCurrent() = 3.584A, TA = +25°C,
unless otherwise noted.)
INPUT CURRENT-LIMIT ERROR
vs. INPUT CURRENT-LIMIT SETTING
INPUT CURRENT-LIMIT SETTING (A)
INPUT CURRENT-LIMIT ERROR (%)
MAX8731 toc0146810
MAXIMUM
MINIMUM
TYPICAL
INPUT CURRENT-LIMIT ERROR
vs. SYSTEM CURRENT
SYSTEM CURRENT (A)
INPUT CURRENT-LIMIT ERROR (%)
MAX8731 toc02
INPUT CURRENT LIMIT = 2.048A
INPUT CURRENT LIMIT = 3.584A
INPUT CURRENT
LIMIT = 4.096A
INPUT CURRENT-LIMIT ERROR
vs. SYSTEM CURRENT
SYSTEM CURRENT (A)
INPUT CURRENT-LIMIT ERROR (%)
MAX8731 toc03
VBATT = 8.4V
VBATT = 16.8V
VBATT = 12.6V
INPUT CURRENT LIMIT = 3.584A
IINP ERROR vs. SYSTEM CURRENT
SYSTEM CURRENT (A)
IINP ERROR (%)
MAX8731 toc04
INPUT CURRENT LIMIT = 2.048A
INPUT CURRENT LIMIT = 3.584A
INPUT CURRENT LIMIT = 4.096A
OPERATING AT INPUT CURRENT LIMIT
IINP ERROR vs. SYSTEM CURRENT
SYSTEM CURRENT (A)
IINP ERROR (%)
MAX8731 toc05
VBATT = 8.4V
VBATT = 12.6V
VBATT = 16.8V
INPUT CURRENT LIMIT = 3.584A
IINP ERROR vs. INPUT CURRENT
INPUT CURRENT (A)
IINP ERROR (%)
MAX8731 toc06
MAXIMUM
MINIMUM
TYPICAL
NOT SWITCHING
CHARGE-CURRENT ERROR vs.
CHARGE CURRENT-LIMIT SETTING
CHARGE-CURRENT LIMIT ERROR (%)
MAX8731 toc07486
MAXIMUM
MINIMUMTYPICAL
CHARGE-CURRENT ERROR
vs. BATTERY VOLTAGE
BATTERY VOLTAGE (V)
CHARGE-CURRENT ERROR (%)
MAX8731 toc0869121518
3.072A3.968A
8.064A
TRICKLE-CHARGE CURRENT ERROR
vs. BATTERY VOLTAGE
TRICKLE-CHARGE CURRENT ERROR (%)
MAX8731 toc09369121518
ChargeCurrent( ) = 128mA
CHARGE-VOLTAGE ERROR
vs. CHARGE-VOLTAGE SETTING
CHARGE-VOLTAGE SETTING (V)
CHARGE-VOLTAGE ERROR (%)
MAX8731 toc108121620
BATTERY-VOLTAGE ERROR
vs. CHARGE CURRENT
CHARGE CURRENT (A)
BATTERY-VOLTAGE ERROR (%)
MAX8731 toc11
3 CELLS
2 CELLS
4 CELLS
BATTERY REMOVAL
20μs/div
MAX8731 toc12
13.5V
13.0V
12.5V
VOUT OUTPUT CAPACITOR = 22μF
ChargeVoltage( ) = 12.6V
VOUT OUTPUT CAPACITOR = 10μF
SYSTEM LOAD TRANSIENT
200μs/div
MAX8731toc13
LOAD
CURRENT
ADAPTER
CURRENT
INDUCTOR
CURRENT
CCS VOLTAGE
500 mV/div
CCI VOLTAGE
500 mV/div
500mV/div
500mV/divCCI
CCS
CCI
CCS
EFFICIENCY vs. CHARGE CURRENT
EFFICIENCY (%)
MAX8731 toc14
2 CELLS
3 CELLS4 CELLS
LDO LOAD REGULATION
LDO ERROR (mV)
MAX8731 toc1520406080100
CHARGER OFF
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
Typical Operating Characteristics(continued)
(Circuit of Figure 1, adapter = 19.5V, ChargeVoltage() = 16.8V, ChargeCurrent() = 3.854A, InputCurrent() = 3.584A, TA = +25°C,
unless otherwise noted.)
Typical Operating Characteristics(continued)
(Circuit of Figure 1, adapter = 19.5V, ChargeVoltage() = 16.8V, ChargeCurrent() = 3.854A, InputCurrent() = 3.584A, TA = +25°C,
unless otherwise noted.)
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
SWITCHING FREQUENCY
VADAPTER - VBATTERY (V)
FREQUENCY (kHz)
MAX8731 toc195101520
BATTERY-CHARGE CURVE
TIME (h)
CHARGE CURRENT (A)
MAX8731 toc20
BATTERY VOLTAGE (V)
BATTERY VOLTAGE
CHARGE CURRENT
2.8Ah x 3S3P BATTERY
ADAPTER CURRENT
vs. ADAPTER VOLTAGE
ADAPTER VOLTAGE (V)
ADAPTER CURRENT (mA)
MAX8731 toc2151015202530
NOT SWITCHING
SWITCHING, NO LOAD
ChargeVoltage( ) = 4.192V
BATTERY-LEAKAGE CURRENT
vs. BATTERY VOLTAGE
BATTERY VOLTAGE (V)
BATTERY CURRENT (
MAX8731 toc225101520
ADAPTER PRESENT OR ABSENT
LDO LINE REGULATION
VDCIN (V)
LDO ERROR (mV)
MAX8731 toc16131823
NOT SWITCHING
REF LOAD REGULATION
IREF (mA)
REF ERROR (%)
MAX8731 toc170.20.40.60.81.0
NOT SWITCHING
REF ERROR vs. TEMPERATURE
TEMPERATURE (°C)
REF ERROR (%)
MAX8731 toc18
0.3
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
Pin Description
PINNAMEFUNCTION1, 12 GND Analog Ground. Connect directly to the paddle.2 ACIN AC Adapter Detect Input. ACIN is the input to an uncommitted comparator.3 REF 4.096V Voltage Reference. Bypass REF with a 1µF capacitor to GND.4 CCS Input Current Regulation Loop-Compensation Point. Connect 0.01µF from CCS to GND.5 CCI Output Current Regulation Loop-Compensation Point. Connect 0.01µF from CCI to GND.6 CCV Voltage Regulation Loop-Compensation Point. Connect 10kΩ in series with 0.01µF to GND.7 DAC DAC Voltage Output. Bypass with 0.1µF from DAC to GND.8 IINP Input Current Monitor Output. IINP sources the current proportional to the current sensed across
CSSP and CSSN. The transconductance from (CSSP - CSSN) to IINP is 3mA/V.9 SDA S M Bus D ata I/O. Op en- d r ai n outp ut. C onnect an exter nal p ul l up r esi stor accor d i ng to S M Bus sp eci fi cati ons.10 SCL SMBus Clock Input. Connect an external pullup resistor according to SMBus specifications.11 VDD Logic Circuitry Supply-Voltage Input. Bypass with a 0.1µF capacitor to GND.13 ACOK AC D etect Outp ut. Thi s op en- d r ai n outp ut i s hi g h i m p ed ance w hen AC IN i s g r eater than RE F/2. The
AC O K outp ut r em ai ns l ow w hen the M AX 8731 i s p ow er ed d ow n. C onnect a 10kΩ p ul l up r esi stor fr om C C to AC O K.14 BATSEL Batter y V ol tag e S el ect Inp ut. D r i ve BATS E L hi g h to sel ect b atter y B, or d r i ve BATS E L l ow to sel ect b atter y A.
Any chang e of BATS E L i m m ed i atel y stop s char g i ng . C har g i ng b eg i ns ag ai n i n ap p r oxi m atel y 10m s.15 FBSA Remote Sense Input for the Output Voltage of Battery A. Connect a 100Ω resistor from FBSA to the
battery connector, and a 10nF capacitor from FBSA to PGND.16 FBSB Remote Sense Input for the Output Voltage of Battery B. Connect a 100Ω resistor from FBSB to the
battery connector, and a 10nF capacitor from FBSB to PGND.17 CSIN Charge Current-Sense Negative Input18 CSIP C har g e C ur r ent- S ense P osi ti ve Inp ut. C onnect a 10m Ω cur r ent- sense r esi stor b etw een C S IP and C S IN .19 PGND Power Ground20 DLO Low-Side Power MOSFET Driver Output. Connect to low-side n-channel MOSFET. DLO drives
between LDO and PGND.21 LDO Linear-Regulator Output. LDO is the output of the 5.4V linear regulator supplied from DCIN. LDO also
directly supplies the DLO driver and the BST charge pump. Bypass with a 1µF ceramic capacitor
from LDO to PGND.22 DCIN Charger Bias Supply Input. Bypass DCIN with a 0.1µF capacitor to PGND.23 LX H i g h- S i d e P ow er M OS FE T D r i ver S our ce C onnecti on. C onnect to the sour ce of the hi g h- si d e n- channel OS FE T.24 DHI High-Side Power MOSFET Driver Output. Connect to the high-side n-channel MOSFET gate.25 BST H i g h- S i d e P ow er M OS FE T D r i ver P ow er - S up p l y C onnecti on. C onnect a 0.1µF cap aci tor fr om BS T to LX .26 VCC D evi ce P ow er - S up p l y Inp ut. C onnect to LD O thr oug h an RC fi l ter as show n i n Fi g ur e 1.27 CSSN Input Current-Sense Negative Input28 CSSP Inp ut C ur r ent- S ense P osi ti ve Inp ut. C onnect a 10m Ω cur r ent- sense r esi stor b etw een C S S P and C S S N .29 BP Backside Paddle. Connect the backside paddle to analog ground.
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
SYSTEM
LOAD
BATTERY
BATTERY
DCIN
CCV
CCI
REF
ACINRS1
10mΩ
N1, N2,: SI4800BDY
N3: SI4810BDY
L1: SUMIDA
CEP125-4R3MC-U
RS2
10mΩ
R13
1kΩ
100kΩR1
150kΩ
49.9kΩ
10kΩ
10kΩ
10kΩ
10kΩ
100Ω
R10100Ω
10kΩ
R12
33Ω
R111Ω
BATSELSELECTOR
SCL
SDA
VDD
CCS
ACOK
VCC
FBSB
FBSA
BST
PGND
CSIN
LDO
CSIP
DLO
LDOLDOLDO
DHI
CIN1
10μF
COUT1
10μF
VOUT
COUT2
10μF
C12
1μF
C11
1μF
1μF
0.1μF
0.1μF
0.01μF
0.01μF
1μFC8
0.1μF
0.01μF
C10
0.1μF220pF
IINP
DAC
CSSP
CSSN
GND
KBC
SCL
INPUT
SDA
VDD
CIN2
10μF
MAX8731
ADAPTER
INPUT
4.3μHN3DHI
Figure 1. Typical Dual-Battery Application Circuit
Detailed Description
The typical operating circuit is shown in Figure 1. The
MAX8731 includes all the functions necessary to
charge Li+, NiMH, and NiCd smart batteries. A high-
efficiency, synchronous-rectified, step-down DC-DC
converter is used to implement a precision constant-
current, constant-voltage charger. The DC-DC convert-
er drives a high-side n-channel MOSFET and provides
synchronous rectification with a low-side n-channel
MOSFET. The charge current and input current-sense
amplifiers have low input-offset error (±64µV typ),
allowing the use of small-valued sense resistors.
The MAX8731 features a voltage-regulation loop (CCV)
and two current-regulation loops (CCI and CCS). The
loops operate independently of each other. The CCV
voltage-regulation loop monitors either FBSA or FBSB
to ensure that its voltage never exceeds the voltage set
by the ChargeVoltage() command. The CCI battery cur-
rent-regulation loop monitors current delivered to the
selected battery to ensure that it never exceeds the
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
ACIN
CSSP
VCC
REF/2
LVC
100mV
IMIN
ENABLE
CCMP
OVP
150mV
(750mA FOR RS2 = 10mΩ)
(10A FOR RS2 = 10mΩ)
IMAX
CSIN
ACOK
GND
CCV
CCI
CSA: CURRENT-SENSE
AMPLIFIER
CCS
LOWEST VOLTAGE CLAMP
4.096V
REFERENCE
5.4V
LINEAR
REGULATOR
CHARGE VOLTAGE ( )
CHARGE CURRENT ( )
INPUT CURRENT ( )
SMBus LOGIC
DC-DC
CONVERTER
11-BIT DAC
6-BIT DAC
6-BIT DACGM
CSA
A = 20V/V
A = 20V/V
A = 1V/V
CHARGE VOLTAGE( )
+100mV
CSACSS
CSI
GMS
IINP
CSSN
CSSP
CSIP
CSIN
BATSEL
FBSBFBSA
DAC
GMI
GMV
MAX8731
LEVEL
SHIFT
BST
DHI
LDO
DLO
PGND
DCIN
REF
SCL
SDA
VDD
VCC
HIGH-
SIDEDRIVER
LOW-SIDE
DRIVER
POWER-FAIL
ZCMD
Figure 2. Functional Diagram
charge current-regulation loop is in control as long as
the selected battery voltage is below the charge volt-
age set point. When the selected battery voltage reach-
es its set point, the voltage-regulation loop takes control
and maintains the battery voltage at the set point. A
third loop (CCS) takes control and reduces the charge
current when the adapter current exceeds the input
current limit set by the InputCurrent() command.
A functional diagram is shown in Figure 2.
MAX8731
SMBus Level 2 Battery Charger with
Remote Sense
BITBIT NAMEDESCRIPTION—Not used. Normally a 1mV weight.—Not used. Normally a 2mV weight.—Not used. Normally a 4mV weight.—Not used. Normally a 8mV weight.Charge voltage, DACV 00 = Adds 0mV of charger voltage compliance, 1024mV min.
1 = Adds 16mV of charger voltage compliance.Charge voltage, DACV 10 = Adds 0mV of charger voltage compliance, 1024mV min.
1 = Adds 32mV of charger voltage compliance.Charge voltage, DACV 20 = Adds 0mV of charger voltage compliance, 1024mV min.
1 = Adds 64mV of charger voltage compliance.Charge voltage, DACV 30 = Adds 0mV of charger voltage compliance, 1024mV min.
1 = Adds 128mV of charger voltage compliance.Charge voltage, DACV 40 = Adds 0mV of charger voltage compliance, 1024mV min.
1 = Adds 256mV of charger voltage compliance.Charge voltage, DACV 50 = Adds 0mV of charger voltage compliance, 1024mV min.
1 = Adds 512mV of charger voltage compliance.Charge voltage, DACV 60 = Adds 0mA of charger voltage compliance.
1 = Adds 1024mV of charger voltage compliance.Charge voltage, DACV 70 = Adds 0mV of charger voltage compliance.
1 = Adds 2048mV of charger voltage compliance.Charge voltage, DACV 80 = Adds 0mV of charger voltage compliance.
1 = Adds 4096mV of charger voltage compliance.Charge voltage, DACV 90 = Adds 0mV of charger voltage compliance.
1 = Adds 8192mV of charger voltage compliance.Charge voltage, DACV 100 = Adds 0mV of charger voltage compliance.
1 = Adds 16,384mV of charger voltage compliance, 19,200mV max.—Not used. Normally a 32,768mV weight.
Table 1. ChargeVoltage () (0x15)
Setting Charge Voltage
To set the output voltage, use the SMBus to write a 16-
bit ChargeVoltage() command using the data format
listed in Table 1. The ChargeVoltage() command uses
the Write-Word protocol (see Figure 3). The command
code for ChargeVoltage() is 0x15 (0b00010101). The
MAX8731 provides a 1.024V to 19.200V charge voltage
range, with 16mV resolution. Set ChargeVoltage()
below 1.024V to terminate charging. Upon reset, the
ChargeVoltage() and ChargeCurrent() values are
cleared and the charger remains off until both the
ChargeVoltage() and the ChargeCurrent() command
are sent. Both DHI and DLO remain low until the charg-
er is restarted.

Partno	Mfg	Dc	Qty	Available	Descript
MAX8731ETI+ \|MAX8731ETI	MAXIM	N/a	1149	avai	SMBus Level 2 Battery Charger with Remote Sense