General Description
The MAX8713 multichemistry battery charger simplifies
construction of smart chargers with a minimum number
of external components. It uses the Intel System
Management Bus (SMBus™) to control the charge volt-
age and charge current. High efficiency is achieved
through the use of a constant off-time step-down topol-
ogy with synchronous rectification.
The MAX8713 charges one to four lithium-ion (Li+) cells
in series and delivers over 2A charge current—scalable
with the sense resistor. The MAX8713 drives n-channel
MOSFETs for improved efficiency and reduced cost. A
low-offset charge-current-sense amplifier provides high-
accuracy charge current with small sense resistors.
The MAX8713 is available in a space-saving 24-pin
4mm x 4mm thin QFN package and operates over the
extended (-40°C to +85°C) temperature range. An eval-
uation kit is available to reduce design time.
Applications
Handset Car Kits
Digital Cameras
PDAs and Tablet Computers
Notebook Computers
Portable Equipment with Rechargeable Batteries
Features
♦Over 2A Charge Current
♦Intel SMBus 2-Wire Serial Interface
♦±0.6% Charge Voltage Accuracy
♦11-Bit Charge Voltage Resolution
♦6-Bit Charge Current Resolution
♦Adjustable Switching Frequency
♦+8V to +28V Input Voltage Range
♦Cycle-By-Cycle Current Limit
♦Charges Any Battery Chemistry (Li+, NiCd, NiMH,
Lead Acid, etc.)
♦Small 24-Pin TQFN
MAX8713
Simplified Multichemistry
SMBus Battery Charger
________________________________________________________________ Maxim Integrated Products 1
19-3498; Rev 0; 11/04
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX8713ETG
-40°C to +85°C
24 Thin QFN 4mm x 4mm
REF 1
IC1 2
CCI 3
CCV 4
DAC 5
VDD 6
DLOV18
DLO17
PGND16
CSIP15
IC314
CSIN13
SDA
7
SCL
8
IC2
9
FREQ
10
GND
11
BATT
12
DCIN
24
LDO
23
DCSNS
22
BST
21
DHI
20
LX
19
MAX8713
*EXPOSED PADDLE
THIN QFN
(4mm x 4mm)
Pin Configuration
SMBus is a trademark of Intel Corp.
MAX8713
DCIN DHI
CSIP
CSIN
BATT
DLOV
LDO
PGND
EXTERNAL
LOAD
N
N
GND
REF
CCI CCV
DLO
BST
LX
DAC
VDD
SCL
SDA
FREQ
BATTERY
DCSNS
HOST
VDD
SCL
SDA
OPTIONAL
Typical Operating Circuit
MAX8713
Simplified Multichemistry
SMBus Battery Charger
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
VDCSNS, VDCIN to GND ..........................................-0.3V to +30V
VBST to GND ..........................................................-0.3V to +36V
VBST to LX ................................................................-0.3V to +6V
VDHI to LX..................................................-0.3V to (VBST + 0.3V)
VLX to GND................................................................-6V to +30V
VDHI to GND ..............................................................-6V to +36V
VBATT, VCSIN to GND .............................................-0.3V to +20V
VCSIP to VCSIN .......................................................-0.3V to +0.3V
PGND to GND .......................................................-0.3V to +0.3V
VCCI, VCCV, VDAC, VREF to GND ..............-0.3V to (VLDO + 0.3V)
VDLOV, VLDO, VDD, VSCL, VSDA, VFREQ to GND ......-0.3V to +6V
VDLO to PGND ........................................-0.3V to (VDLOV + 0.3V)
LDO Short-Circuit Current...................................................25mA
Continuous Power Dissipation (TA= +70°C)
24-Pin Thin QFN 4mm x 4mm (derate 20.8mW/°C
above +70°C).............................................................1667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= 0°C to +85°C, unless otherwise noted. Typical
values are at TA= +25°C.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
CHARGE VOLTAGE REGULATION
ChargingVoltage() = 0x20D0
-0.6
+0.6
ChargingVoltage() = 0x1060
-1.0
+1.0
Battery Regulation Voltage Accuracy
ChargingVoltage() = 0x41A0 and 0x3130
-0.8
+0.8
%
ChargingVoltage() = 0x41A0, VDCIN = 19V
16.668 16.8 16.934
ChargingVoltage() = 0x3130, VDCIN = 19V
12.491 12.592 12.693
ChargingVoltage() = 0x20D0, VDCIN = 12V
8.439
8.4
8.442
Battery Full Charge Voltage
ChargingVoltage() = 0x1060, VDCIN = 12V
4.150 4.192 4.234
V
CHARGE CURRENT REGULATION
CSIP to CSIN Full-Scale Current-Sense
Voltage VBATT = 8.4V, VDCIN = 12V
78.22 80.64 88.05
mV
ChargingCurrent() = 0x07e0 -3 +3
Compliance Current Accuracy ChargingCurrent() = 0x03e0 -5 +5
%
ChargingCurrent() = 0x07e0
78.22 80.64 83.05
ChargingCurrent() = 0x03e0
37.68 39.68 41.68
ChargingCurrent() = 0x0180
13.82 15.36 16.88
Battery Charge Current-Sense Voltage
ChargingCurrent() = 0x0020
1.28
mV
BATT/CSIP/CSIN Input Voltage Range 0 19 V
VDCIN = 0 or charger not switching 0.1 1 µA
CSIP/CSIN Input Current VCSIP = VCSIN = 19V
700
µA
SUPPLY AND LINEAR REGULATOR
DCIN Input Voltage Range 7.5
28.0
V
DCSNS Input Voltage Range 7.5
28.0
V
MAX8713
Simplified Multichemistry
SMBus Battery Charger
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= 0°C to +85°C, unless otherwise noted. Typical
values are at TA= +25°C.)
PARAMETER CONDITIONS
MIN TYP MAX
UNITS
DCIN falling 6.5 7
DCIN Undervoltage-Lockout Trip Point DCIN rising 7 7.5
V
DCIN Quiescent Current 7.5V < VDCIN < 28V 2.7 6
mA
DCSNS Quiescent Current 7.5V < VDCSNS < 28V
200 300
µA
VBATT = 19V, VDCIN = 0 or charger not switching 0.1 1
BATT Input Current VBATT = 2V to 19V, VDCIN > VBATT + 0.3V
200 500
µA
LDO Output Voltage 7.5V < VDCIN < 28V, no load
5.25
5.4
5.55
V
LDO Load Regulation 0 < ILDO < 5mA 34
100
mV
LDO Undervoltage-Lockout Trip Point VDCIN = 7.5V
3.20
4
5.15
V
VDD Range 2.7 5.5 V
VDD UVLO Rising 2.5 2.7 V
VDD UVLO Hysteresis
100
mV
VDD Quiescent Current VDCIN < 6V, VDD = 5.5V, VSCL = VSDA = 5.5V 27 µA
REFERENCE
REF Output Voltage 0 < IREF < 500µA
4.067 4.096 4.125
V
REF Undervoltage-Lockout Trip Point REF falling 3.1 3.9 V
TRIP POINTS
BATT POWER_FAIL Threshold VDCSNS falling 50
100 150
mV
BATT POWER_FAIL Threshold Hysteresis
50
200 400
mV
SWITCHING REGULATOR
RFREQ = 100kΩ 675 750 825
VBATT = 8.4V RFREQ = 400kΩ 2700 3000 3300
RFREQ = 100kΩ 370 410 450
Off-Time
VBST - VLX = 4.5V
VBATT = 11V RFREQ = 400kΩ 1476 1640 1804
ns
DLOV Supply Current Charger not switching 5 10 µA
BST Supply Current DHI high 6 15 µA
BST Input Quiescent Current VDCIN = 0V, VBST = 23.5V, VBATT = VLX = 19V 0.3 1 µA
LX Input Bias Current VDCIN = 28V, VBATT = VLX = 19V
150 500
µA
Maximum Discontinuous-Mode Peak
Current
0.125
A
DHI On-Resistance High VBST =12.9V, VBATT = 8.4V, VDCSNS = 12,
DHI = VLX; IDHI = -10mA 7 14 Ω
DHI On-Resistance Low VBST =12.9V, VBATT = 8.4V, VCSNS = 12,
DHI = VBST; IDHI = +100mA 2 4 Ω
DLO On-Resistance High VDLOV = 4.5V, IDLO = -10mA 7 14 Ω
DLO On-Resistance Low VDLOV = 4.5V, IDLO = +100mA 2 4 Ω
ERROR AMPLIFIERS
GMV Amplifier Transconductance ChargingVoltage() = 0x20d0, VBATT = 8.400V
0.0625 0.125 0.2500
mA/V
MAX8713
Simplified Multichemistry
SMBus Battery Charger
4_______________________________________________________________________________________
TIMING CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= 0°C to +85°C, unless otherwise noted. Typical
values are at TA= +25°C.)
PARAMETER
SYM B O L
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus TIMING SPECIFICATION (VDD = 2.7V TO 5.5V) (Figures 6 and 7)
SMBus Frequency fSMB 10
100
kHz
Bus Free Time tBUF 4.7 µs
Start Condition Hold Time from SCL tHD:STA 4 µs
Start Condition Setup Time from SCL
tSU:STA 4.7 µs
Stop Condition Setup Time from SCL
tSU:STO 4 µs
SDA Hold Time from SCL tHD:DAT
300
ns
SDA Setup Time from SCL tSU:DAT
250
ns
SCL Low Timeout
tTIMEOUT
(Note 1) 25 35 ms
SCL Low Period tLOW 4.7 µs
SCL High Period tHIGH 4 µs
Cumulative Clock Low Extend Time
tLOW:SEXT
(Note 2) 25
ms
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= 0°C to +85°C, unless otherwise noted. Typical
values are at TA= +25°C.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
GMI Amplifier Transconductance ChargingCurrent() = 0x03e0,
VCSIP - VCSIN = 39.68mV 0.5 1 2.0
mA/V
CCI/CCV Clamp Voltage 0.25V < VCCV/I < 2.0V
150 300 600
mV
SMBus INTERFACE LEVEL SPECIFICATIONS
SDA/SCL Input Low Voltage VDD = 2.7V to 5.5V 0.8 V
SDA/SCL Input High Voltage VDD = 2.7V to 5.5V 2.1 V
SDA/SCL Input Bias Current VDD = 2.7V to 5.5V -1 +1 µA
SDA, Output Sink Current V(SDA) = 0.4V 6
mA
MAX8713
Simplified Multichemistry
SMBus Battery Charger
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
CHARGE VOLTAGE REGULATION
ChargingVoltage() = 0x20D0
-1.0
+1.0
ChargingVoltage() = 0x1060
-1.5
+1.5
Battery Regulation Voltage Accuracy
ChargingVoltage() = 0x41A0 and 0x3130
-1.2
+1.2
%
ChargingVoltage() = 0x41A0, VDCIN = 19V
16.598
17.002
ChargingVoltage() = 0x3130, VDCIN = 19V
12.441
12.743
ChargingVoltage() = 0x20D0, VDCIN = 12V
8.312
8.484
Battery Full Charge Voltage
ChargingVoltage() = 0x1060, VDCIN = 12V
4.124
4.253
V
CHARGE CURRENT REGULATION
CSIP to CSIN Full-Scale Current-Sense
Voltage VBATT = 8.4V, VDCIN = 12V
78.22
83.05
mV
ChargingCurrent() = 0x07e0 -3 +3
Compliance Current Accuracy ChargingCurrent() = 0x03e0 -5 +5
%
ChargingCurrent() = 0x07e0
78.22
83.05
ChargingCurrent() = 0x03e0
37.68
41.68
Battery Charge Current-Sense Voltage
ChargingCurrent() = 0x0180
13.056
17.664
mV
BATT/CSIP/CSIN Input Voltage Range 0 19 V
VDCIN = 0 or charger not switching 1 µA
CSIP/CSIN Input Current VCSIP = VCSIN = 19V
700
µA
SUPPLY AND LINEAR REGULATOR
DCIN Input Voltage Range 7.5
28.0
V
DCSNS Input Voltage Range 7.5
28.0
V
DCIN falling 6.5
DCIN Undervoltage-Lockout Trip Point DCIN rising 7.5
V
DCIN Quiescent Current 7.5V < VDCIN < 28V 6
mA
DCSNS Quiescent Current 7.5V < VDCSNS < 28V
300
µA
VBATT = 19V, VDCIN = 0 or charger not switching 1
BATT Input Current VBATT = 2V to 19V, VDCIN > VBATT + 0.3V
500
µA
LDO Output Voltage 7.5V < VDCIN < 28V, no load
5.25
5.55
V
LDO Load Regulation 0 < ILDO < 5mA
100
mV
LDO Undervoltage-Lockout Trip Point VDCIN = 7.5V
3.20
5.15
V
VDD Range 2.7 5.5 V
VDD UVLO Rising 2.7 V
VDD Quiescent Current VDCIN < 6V, VDD = 5.5V, VSCL = VSDA = 5.5V 27 µA
REFERENCE
REF Output Voltage 0 < IREF < 500µA
4.053
4.133
V
REF Undervoltage-Lockout Trip Point REF falling 3.9 V
MAX8713
Simplified Multichemistry
SMBus Battery Charger
6_______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
TRIP POINTS
BATT POWER_FAIL Threshold VDCSNS falling 50
150
mV
BATT POWER_FAIL Threshold Hysteresis
50
400
mV
SWITCHING REGULATOR
RFREQ = 100kΩ 637
862
VBATT = 8.4V RFREQ = 400kΩ 2550
3450
RFREQ = 100kΩ 350
470
Off-Time
VBST - VLX = 4.5V
VBATT = 11V RFREQ = 400kΩ 1394
1866
ns
DLOV Supply Current Charger not switching 10 µA
BST Supply Current DHI high 15 µA
BST Input Quiescent Current VDCIN = 0V, VBST = 23.5V, VBATT = VLX = 19V 1 µA
LX Input Bias Current VDCIN = 28V, VBATT = VLX = 19V
500
µA
DHI On-Resistance High VBST =12.9V, VBATT = 8.4V, VDCSNS = 12,
DHI= VLX; IDHI = -10mA 14 Ω
DHI On-Resistance Low VBST =12.9V, VBATT = 8.4V, VCSNS = 12,
DHI = VBST; IDHI = +100mA 4 Ω
DLO On-Resistance High VDLOV = 4.5V, IDLO = -10mA 14 Ω
DLO On-Resistance Low VDLOV = 4.5V, IDLO = +100mA 4 Ω
ERROR AMPLIFIERS
GMV Amplifier Transconductance ChargingVoltage() = 0x20d0, VBATT = 8.384V
0.0625
0.2500
mA/V
GMI Amplifier Transconductance ChargingCurrent() = 0x03e0,
VCSIP - VCSIN = 39.68mV 0.5 2.0
mA/V
CCI/CCV Clamp Voltage 0.25V < VCCV/I < 2.0V
130
600
mV
SMBus INTERFACE LEVEL SPECIFICATIONS
SDA/SCL Input Low Voltage VDD = 2.7V to 5.5V 0.8 V
SDA/SCL Input High Voltage VDD = 2.7V to 5.5V 2.2 V
SDA/SCL Input Bias Current VDD = 2.7V to 5.5V -1 +1 µA
SDA, Output Sink Current V(SDA) = 0.4V 6
mA
MAX8713
Simplified Multichemistry
SMBus Battery Charger
_______________________________________________________________________________________ 7
TIMING CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1µF,
CDAC = 0.1µF , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA= -40°C to +85°C, unless otherwise noted.) (Note 3)
PARAMETER
SYM B O L
CONDITIONS
MIN TYP MAX
UNITS
SMBus TIMING SPECIFICATION (VDD = 2.7V TO 5.5V) (Figures 6 and 7)
SMBus Frequency fSMB 10
100
kHz
Bus Free Time tBUF 4.7 µs
Start Condition Hold Time from SCL tHD:STA 4 µs
Start Condition Setup Time from SCL
tSU:STA 4.7 µs
Stop Condition Setup Time from SCL
tSU:STO 4 µs
SDA Hold Time from SCL tHD:DAT
300
ns
SDA Setup Time from SCL tSU:DAT
250
ns
SCL Low Timeout
tTIMEOUT
(Note 1) 25 35 ms
SCL Low Period tLOW 4.7 µs
SCL High Period tHIGH 4 µs
Cumulative Clock Low Extend Time
tLOW:SEXT
(Note 2) 25
ms
Note 1: Devices participating in a transfer timeout when any clock low exceeds the tTIMEOUT:MIN value of 25ms. Devices that have
detected a timeout condition must reset the communication no later than tTIMEOUT:MAX of 35ms. The maximum value speci-
fied must be adhered to by both a master and a slave as it incorporates the cumulative stretch limit for both a master
(10ms) and a slave (25ms).
Note 2: tLOW:SEXT is the cumulative time a slave device is allowed to extend the clock cycles in one message from the initial start to
the stop. If a slave device exceeds this time, it is expected to release both its clock and data lines and reset itself.
Note 3: Specifications to -40°C are guaranteed by design and not production tested.
LDO LOAD REGULATION
MAX8713 toc01
ILDO (mA)
VLDO (V)
45403530252015105
5.32
5.34
5.36
5.38
5.40
5.42
5.44
5.30
050
CHARGER NOT SWITCHING
LDO LINE REGULATION
MAX8713 toc02
INPUT VOLTAGE (V)
VLDO (V)
262420 2212 14 16 1810
5.320
5.325
5.330
3.335
3.340
3.345
5.350
5.355
5.360
5.315
828
CHARGER SWITCHING
REFERENCE LOAD REGULATION
MAX8713 toc03
IREF (µA)
VREF (V)
900800700600500400300200100
4.0955
4.0960
4.0965
4.0970
4.0975
4.0980
4.0950
01000
__________________________________________Typical Operating Characteristics
(VDCIN = VDCSNS = 20V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
MAX8713
Simplified Multichemistry
SMBus Battery Charger
8_______________________________________________________________________________________
REFERENCE VOLTAGE
vs. TEMPERATURE
MAX8713 toc04
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
806020 400-20
4.082
4.084
4.086
4.088
4.090
4.092
4.094
4.096
4.098
4.100
4.080
-40
EFFICIENCY vs. CHARGE CURRENT
MAX8713 toc05
CHARGE CURRENT (A)
EFFICIENCY (%)
1.81.61.2 1.40.4 0.6 0.8 1.00.2
10
20
30
40
50
60
70
80
90
100
0
0 2.0
VBATT = 16.8V
VBATT = 12.6V
VBATT = 8.4V
VBATT = 4.2V
FREQUENCY vs. RFREQ
MAX8713 toc06
RFREQ (kΩ)
FREQUENCY (kHz)
400300200100
100
200
300
400
500
600
700
0
0500
FREQUENCY vs. VIN
MAX8713 toc07
INPUT VOLTAGE (V)
FREQUENCY (kHz)
262420 2212 14 16 1810
50
100
150
200
250
300
350
400
450
0
828
VBATT = 4.2V
VBATT = 8.4V
VBATT = 12.6V
VBATT = 16.8V
ADAPTER CURRENT
vs. ADAPTER VOLTAGE
MAX8713 toc10
ADAPTER VOLTAGE (V)
ADAPTER CURRENT (mA)
2015105
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
025
CHARGER
SWITCHING,
NO LOAD
CHARGER NOT
SWITCHING
CHARGE-CURRENT ERROR
vs. BATTERY VOLTAGE
MAX8713 toc08
VBATT (V)
CHARGE-CURRENT ERROR (%)
181612 146 8 104
-8
-6
-4
-2
0
2
4
6
8
10
-10
220
CHARGECURRENT() = 0.992A
CHARGECURRENT() = 2A
CHARGE-CURRENT ERROR
vs. CHARGE-CURRENT SETTING
MAX8713 toc09
CHARGE-CURRENT SETTING (A)
CHARGE-CURRENT ERROR (%)
2.01.51.00.5
-4
-3
-2
-1
0
1
2
3
4
5
-5
02.5
BATTERY CURRENT
vs. BATTERY VOLTAGE
MAX8713 toc11
BATTERY VOLTAGE (V)
BATTERY CURRENT (µA)
18161412108642
1
2
3
4
5
6
0
020
ADAPTER ABSENT
ADAPTER PRESENT
____________________________Typical Operating Characteristics (continued)
(VDCIN = VDCSNS = 20V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
MAX8713
Simplified Multichemistry
SMBus Battery Charger
_______________________________________________________________________________________ 9
BATTERY-VOLTAGE ERROR
vs. CHARGE VOLTAGE SETTING
MAX8713 toc12
CHARGE VOLTAGE SETTING (V)
BATTERY-VOLTAGE ERROR (mV)
15105
-80
-60
-40
-20
0
20
-100
020
BATTERY-VOLTAGE ERROR vs. LOAD
MAX8713 toc13
LOAD CURRENT (A)
BATTERY-VOLTAGE ERROR (mV)
1.51.00.5
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
-50
0 2.0
____________________________Typical Operating Characteristics (continued)
(VDCIN = VDCSNS = 20V, Circuit of Figure 1, TA = +25°C, unless otherwise noted.)
PIN
NAME
FUNCTION
1REF 4.096V Voltage Reference. Bypass REF with a 1µF capacitor to GND.
2IC1 Internally Connected. Connect to the exposed paddle for improved layout.
3CCI Output Current-Regulation Loop Compensation Point. Connect 0.01µF to GND.
4CCV Voltage-Regulation Loop Compensation Point. Connect 10kΩ in series with 0.01µF to GND.
5DAC DAC Voltage Output. Bypass with a 0.1µF capacitor to GND.
6V
DD Logic Circuitry Supply Voltage Input. Bypass with a 0.1µF capacitor to GND.
7SDA SMBus Data IO. Open-drain output. Connect the external pullup resistor according to SMBus specifications.
8SCL SMBus Clock Input. Connect the external pullup resistor according to SMBus specifications.
9IC2 Internally Connected. Connect to the exposed paddle for improved layout.
10
FREQ tOFF Frequency Adjust Input. Connect a 100kΩ to 400kΩ resistor between FREQ and GND to set the PWM
frequency.
11
GND Analog Ground
12
BATT Battery Voltage Sense Input
13
CSIN Output Current-Sense Negative Input
14
IC3 Internally Connected. Connect to the exposed paddle for improved layout.
15
CSIP Output Current-Sense Positive Input. Connect a current-sense resistor from CSIP to CSIN.
16
PGND
Power Ground
17
DLO Low-Side Power MOSFET Driver Output. Connect to the low-side n-channel MOSFET gate.
18
DLOV Low-Side Driver Supply. Bypass DLOV with a 1µF capacitor to PGND. Connect a 33Ω resistor from LDO to
DLOV for filtering.
Pin Description
MAX8713
Simplified Multichemistry
SMBus Battery Charger
10 ______________________________________________________________________________________
PIN
NAME
FUNCTION
19
LX High-Side Power MOSFET Driver Power-Supply Connection. Connect a 0.1µF capacitor from BST to LX.
20
DHI High-Side Power MOSFET Driver Output. Connect to the high-side n-channel MOSFET gate.
21
BST High-Side Power MOSFET Driver Power-Supply Connection. Connect a 0.1µF capacitor from BST to LX.
22
DCSNS
DC Supply-Voltage Sense Input. Charging is disabled for VDCSNS < VCSIN + 100mV. DCSNS is also used to
calculate the switching regulator’s off-time.
23
LDO Device Power Supply. LDO is the output of the 5.4V linear regulator supplied from DCIN. Bypass LDO with a
1µF ceramic capacitor from LDO to GND.
24
DCIN Charger Bias Supply Input. Bypass DCIN with a 0.1µF ceramic capacitor to PGND.
Pin Description (continued)
Figure 1. Typical Application Circuit
MAX8713
DCIN DHI
CSIP
CSIN
BATT
DLOV
LDO
PGND
24
23
EXTERNAL
LOAD
RS
40mΩ
L1
22µH
C12
1µF
C11
1µF
M2
M1
GND
22
REF
1
CCI
C8
0.01µF
3
CCV 4
R5
10kΩ
C9
0.01µF
R6
33Ω
C1
0.1µF
C3
1µF
C7
0.1µF
DLO
C2
22µF
C5
10µF
BST
LX
D3
DAC
2
C4
0.1µF
VDD
6
SCL
8
SDA
7
FREQ
10
R3
100kΩ
BATTERY
11
18
12
13
15
16
17
19
20
21
DCSNS
D1
D2
BATT+
BATTERY
BATT-
SCL
SDA
HOST
VDD
SCL
SDA
C6
0.1µF
ADAPTER
Detailed Description
The MAX8713 includes all of 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-sense amplifier has a low
input offset error, allowing the use of small-valued
sense resistors. The MAX8713 features a voltage-regu-
lation loop (CCV) and a current-regulation loop (CCI).
CCI and CCV operate independently of each other. The
CCV voltage-regulation loop monitors BATT to ensure
that its voltage never exceeds the voltage set by the
ChargeVoltage() command. The CCI battery current-
regulation loop monitors current delivered to BATT to
ensure that it never exceeds the current limit set by the
ChargeCurrent() command. The charge current-regula-
tion loop is in control as long as the BATT voltage is
below the set point. When the BATT voltage reaches its
set point, the voltage-regulation loop takes control and
maintains the battery voltage at the set point.
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________ 11
Figure 2. Functional Diagram
MAX8713
GMV
BATT
CCV
LOWEST
VOLTAGE CLAMP
DC-DC
CONVERTER
SMBus LOGIC
DHI
DLO
PGND
DLOV
LX
BST
LEVEL
SHIFT
LOW-
SIDE
DRIVER
HIGH-
SIDE
DRIVER
GND
6-BIT DAC
SCL
SDA
5.4V LINEAR
REGULATOR
4.096V
REFERENCE
11-BIT DAC
A = 20V/V
CSIP
CSIN
GMI
CCI
CSI
CURRENT-
SENSE
AMPLIFIER
CCMP
0.1V
IMIN
IMAX
150mV
(188mA FOR 40mΩ)
IZX
2V
(2.5A FOR 40mΩ)
OFF-TIME GENERATOR
REF
LDO
DCIN
DCSNS
FREQ
ChargingVoltage()
ChargingVoltage()
DAC
LVC
MAX8713
The circuit shown in Figure 1 demonstrates a typical
application for smart-battery systems. A functional dia-
gram is shown in Figure 2.
Setting Charge Voltage
To set the output voltage of the MAX8713, use the
SMBus to write a 16-bit ChargeVoltage() command.
This 16-bit command translates to a 1mV LSB and a
65.535V full-scale voltage. The MAX8713 ignores the
first 4 LSBs and uses the next 11 bits to set the voltage
DAC. The charge voltage range of the MAX8713 is 0 to
19.200V. All codes requesting charge voltage greater
than 19.200V result in a voltage setting of 19.200V. All
codes requesting charge voltage below 1.024V result in
a voltage set point of zero, which terminates charging.
Upon reset, the ChargeVoltage() and ChargeCurrent()
values are cleared and the charger remains shut down
until a ChargeVoltage() and ChargeCurrent() command
is sent.
The ChargeVoltage() command uses the Write-Word
protocol (Figure 5). The command code for
ChargeVoltage() is 0x15 (0b00010101). The 16-bit
binary number formed by D15–D0 represents the
charge-voltage set point in mV. However, the resolution
of the MAX8713 is 16mV in setting the charge voltage
because the D0–D3 bits are ignored as shown in Table
1. The D15 bit is also ignored because it is not needed
to span the 0 to 19.2V range. Figure 3 shows the map-
ping between the charge-voltage set point and the
ChargeVoltage() code. All codes requesting charge
voltage greater than 19.200V result in a 19.200V set-
ting. All codes requesting charge voltage below
1024mV result in a voltage set point of zero, which ter-
minates charging.
Upon initial power-up, ChargingVoltage() is reset to
zero and a ChargingVoltage() command must be sent
to initiate charging.
Setting Charge Current
To set the charge current for the MAX8713, use the
SMBus interface to write a 16-bit ChargeCurrent() com-
mand. This 16-bit command translates to a 1mA per
LSB and a 65.535A full-scale current using a 40mΩ
current-sense resistor (RS in Figure 1). Equivalently, the
ChargeCurrent() value sets the voltage across the CSIP
and CSIN inputs in 40µV increments. The MAX8713
ignores the lowest 5 LSBs and uses the next 6 bits to
set the current DAC. The charge current range is 0 to
2.016A using a 40mΩcurrent-sense resistor. All codes
requesting charge current above 2.016A result in a set-
ting of 2.016A. For larger current settings, scale down
the sense resistor. All codes requesting charge current
between 1mA to 32mA result in a current setting of
32mA. To stop charging, set ChargeCurrent() to 0.
Upon initial power-up, the ChargeVoltage() and
ChargeCurrent() values are cleared and the charger
remains shut down. To start the charger, send valid
ChargeVoltage() and ChargeCurrent() commands.
The ChargeCurrent() command uses the Write-Word
protocol (Figure 5). The command code for
ChargeCurrent() is 0x14 (0b00010100). Table 2 shows
the format of the ChargeCurrent() register. Figure 4
shows the mapping between the charge-current set
point and the ChargeCurrent() code. The default
charge current setting at power-up is 0mA.
LDO Regulator
An integrated low-dropout (LDO) linear regulator pro-
vides a 5.4V supply derived from DCIN, and delivers
over 5mA of load current. The LDO powers the gate dri-
vers of the n-channel MOSFETs in the DC-DC converter.
See the MOSFET Drivers section. The LDO also biases
the 4.096V reference and most of the control circuitry.
Bypass LDO to GND with a 1µF ceramic capacitor.
VDD Supply
The VDD input provides power to the SMBus interface.
Connect VDD to LDO, or apply an external supply to
VDD to keep the SMBus interface active while the sup-
ply to DCIN is removed. When VDD is biased, the inter-
nal registers are maintained. Bypass VDD to GND with
a 0.1µF ceramic capacitor.
Operating Conditions
Table 3 is a summary of operating states of the
MAX8713.
•Adapter Present. When DCIN is greater than 7.5V,
the adapter is considered to be present. In this con-
dition, both the LDO and REF function properly and
battery charging is allowed.
•Power Fail. When DCIN is less than BATT + 0.3V,
the MAX8713 is in the power-fail state, since the
DC-DC converter is in dropout. The charger will not
attempt to charge when in the power-fail state.
•V
DD Undervoltage. When VDD is less than 2.5V,
the VDD supply is considered to be in an undervolt-
age state. The SMBus interface does not respond to
commands. When coming out of the undervoltage
condition, the part is in its power-on reset state. No
charging occurs when VDD is in the undervoltage
state. When VDD is greater than 2.5V, SMBus regis-
ters are preserved.
Simplified Multichemistry
SMBus Battery Charger
12 ______________________________________________________________________________________
SMBus Interface
The MAX8713 receives control inputs from the SMBus
interface. The serial interface complies with the SMBus
protocols as documented in the System Management
Bus Specification V1.1, which can be downloaded from
www.smbus.org. The MAX8713 uses the SMBus Read-
Word and Write-Word protocols (Figure 5) to communi-
cate with the smart battery. The MAX8713 is an SMBus
slave device and does not initiate communication on
the bus. It responds to the 7-bit address 0b0001001_
(0x12). In addition, the MAX8713 has two identification
(ID) registers: a 16-bit device ID register and a 16-bit
manufacturer ID register.
The data (SDA) and clock (SCL) pins have Schmitt-trig-
ger inputs that can accommodate slow edges. Choose
pullup resistors for SDA and SCL to achieve rise times
according to the SMBus specifications.
Communication starts when the master signals a START
condition, which is a high-to-low transition on SDA,
while SCL is high. When the master has finished com-
municating, the master issues a STOP condition, which
is a low-to-high transition on SDA, while SCL is high.
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________ 13
Table 1. ChargeVoltage()
BIT BIT NAME DESCRIPTION
0—Not used. Normally a 1mV weight.
1—Not used. Normally a 2mV weight.
2—Not used. Normally a 4mV weight.
3—Not used. Normally an 8mV weight.
4Charge Voltage, DACV 0 0 = Adds 0mV of charge-voltage compliance, 1024mV (min).
1 = Adds 16mV of charge-voltage compliance.
5Charge Voltage, DACV 1 0 = Adds 0mV of charge-voltage compliance, 1024mV (min).
1 = Adds 32mV of charge-voltage compliance.
6Charge Voltage, DACV 2 0 = Adds 0mV of charge-voltage compliance, 1024mV (min).
1 = Adds 64mV of charge-voltage compliance.
7Charge Voltage, DACV 3 0 = Adds 0mV of charge-voltage compliance, 1024mV (min).
1 = Adds 128mV of charge-voltage compliance.
8Charge Voltage, DACV 4 0 = Adds 0mV of charge-voltage compliance, 1024mV (min).
1 = Adds 256mV of charge-voltage compliance.
9Charge Voltage, DACV 5 0 = Adds 0mV of charge-voltage compliance, 1024mV (min).
1 = Adds 512mV of charge-voltage compliance.
10 Charge Voltage, DACV 6 0 = Adds 0mV of charge-voltage compliance.
1 = Adds 1024mV of charge-voltage compliance.
11 Charge Voltage, DACV 7 0 = Adds 0mV of charge-voltage compliance.
1 = Adds 2048mV of charge-voltage compliance.
12 Charge Voltage, DACV 8 0 = Adds 0mV of charge-voltage compliance.
1 = Adds 4096mV of charge-voltage compliance.
13 Charge Voltage, DACV 9 0 = Adds 0mV of charge-voltage compliance.
1 = Adds 8192mV of charge-voltage compliance.
14
Charge Voltage, DACV 10
0 = Adds 0mV of charge-voltage compliance.
1 = Adds 16,384mV of charge-voltage compliance, 19,200mV (max).
15 — Not used. Normally a 32,768mV weight.
Command: 0x15
MAX8713
Table 2. ChargeCurrent()
BIT BIT NAME DESCRIPTION
0—Not used. Normally a 1mA weight.
1—Not used. Normally a 2mA weight.
2—Not used. Normally a 4mA weight.
3—Not used. Normally an 8mA weight.
4—Not used. Normally a 16mA weight.
5
Charge Current DAC, bit 0
0 = Adds 0mA of charger current compliance.
1 = Adds 32mA of charger current compliance.
6
Charge Current DAC, bit 1
0 = Adds 0mA of charger current compliance.
1 = Adds 64mA of charger current compliance.
7
Charge Current DAC, bit 2
0 = Adds 0mA of charger current compliance.
1 = Adds 128mA of charger current compliance.
8
Charge Current DAC, bit 3
0 = Adds 0mA of charger current compliance.
1 = Adds 256mA of charger current compliance.
9
Charge Current DAC, bit 4
0 = Adds 0mA of charger current compliance.
1 = Adds 512mA of charger current compliance.
10
Charge Current DAC, bit 5
0 = Adds 0mA of charger current compliance.
1 = Adds 1024mA of charger current compliance. 2016mA (max).
11 — Not used. Normally a 2048mA weight.
12 — Not used. Normally a 4096mA weight.
13 — Not used. Normally a 8192mA weight.
14 — Not used. Normally a 16,384mA weight.
15 — Not used. Normally a 32,768mA weight.
Command: 0x14
The bus is then free for another transmission. Figures 6
and 7 show the timing diagram for signals on the
SMBus interface. The address-byte, command-byte,
and data-bytes are transmitted between the START and
STOP conditions. The SDA state is allowed to change
only while SCL is low, except for the START and STOP
conditions. Data is transmitted in 8-bit bytes and is
sampled on the rising edge of SCL. Nine clock cycles
are required to transfer each byte in or out of the
MAX8713 because either the master or the slave
acknowledges the receipt of the correct byte during the
ninth clock. The MAX8713 supports the charger com-
mands as described in Tables 2–4.
Battery Charger Commands
The MAX8713 supports four battery-charger com-
mands that use either Write-Word or Read-Word proto-
cols, as summarized in Table 2. ManufacturerID() and
DeviceID() can be used to identify the MAX8713. On
the MAX8713, ManufacturerID() always returns 0x004D
and DeviceID() always returns 0x0007.
DC-DC Converter
The MAX8713 employs a pseudo-fixed-frequency, cur-
rent-mode control scheme with cycle-by-cycle current
limit. The controller’s constant off-time (tOFF) is calculat-
ed based on VDCIN, VBATT, and RFREQ, and has a min-
imum value of 300ns. The operation of the DC-DC
controller is determined by the following four compara-
tors as shown in the functional diagram (Figure 2):
Simplified Multichemistry
SMBus Battery Charger
14 ______________________________________________________________________________________
The IMIN comparator sets the peak inductor current in
discontinuous mode. IMIN compares the control signal
(LVC) against 100mV (typ). When LVC voltage is less
than 100mV, DHI and DLO are both low.
The CCMP comparator is used for current-mode regu-
lation in continuous-conduction mode. CCMP com-
pares LVC against the charging-current feedback
signal (CSI). The comparator output is high and the
high-side MOSFET on-time is terminated when the CSI
voltage is higher than LVC.
The IMAX comparator provides a cycle-by-cycle cur-
rent limit. IMAX compares CSI to 2V (corresponding to
2.5A when RS = 40mΩ). The comparator output is high
and the high-side MOSFET on-time is terminated when
the current-sense signal exceeds 2.5A. A new cycle
cannot start until the IMAX comparator output goes low.
The ZCMP comparator provides zero-crossing detec-
tion during discontinuous conduction. ZCMP compares
the current-sense feedback signal to 188mA (RS =
40mΩ). When the inductor current is lower than the
188mA threshold, the comparator output is high and
DLO is turned off.
Setting the Switching Frequency
The MAX8713 features an adjustable switching fre-
quency. To set the switching frequency, choose RFREQ
according to the following equation:
Higher switching frequencies are typically preferred to
minimize inductor and capacitor requirements. See the
Typical Operating Characteristics. The switching fre-
quency has a minor dependence on VDCIN and VBATT
because of voltage losses along the high current path
and other 2nd-order effects not accounted in the
MAX8713’s off-time calculation. These can be account-
ed for by observing the curves in the Typical Operating
Characteristics.
RFREQ SWITCH
100kHz 400k
f
=×Ω
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________ 15
1024
4200
8400
19200
16800
0xFFFF0x0400 0x1060 0x20D0 0x4B000x41A0
CHARGEVOLTAGE() CODE
CHARGE-VOLTAGE SET POINT (mV)
Figure 3. ChargeVoltage() Code to Charge-Voltage Set-Point
Mapping
32
512
1024
2016
0xFFFF0x0020 0x0200 0x0400 0x07E0
CHARGECURRENT() CODE
CHARGE-CURRENT SET POINT (mA)
Figure 4. ChargeCurrent() Code to Charge-Current Set Point
Mapping (R2= 40mΩ)
Table 3. Summary of Operating States
OPERATING STATES
INPUT CONDITIONS ADAPTER PRESENT POWER FAIL VDD UNDERVOLTAGE
DCIN VDCIN > 7.5V VDCIN < VBATT + 0.1V X
BATT XV
BATT > VDCIN - 0.1V X
VDD XXV
DD < 2.5V
X = Don’t care.
MAX8713
CCV, CCI, and LVC Control Blocks
The MAX8713 controls charge current (CCI control
loop) or charge voltage (CCV control loop), depending
on the operating condition. The two control loops CCV
and CCI are brought together internally at the LVC (low-
est voltage clamp) amplifier. The output of the LVC
amplifier is the feedback control signal for the DC-DC
controller. The minimum voltage of CCV and CCI
appears at the output of the LVC amplifier and clamps
the remaining control loop to within 0.3V above the con-
trol point. Clamping the other control loop close to the
lowest control loop ensures fast transition with minimal
overshoot when switching between different regulation
modes (see the Compensation section).
Continuous-Conduction Mode
With sufficient charge current, the MAX8713’s inductor
current never crosses zero, which is defined as continu-
ous-conduction mode. The regulator switches at
400kHz (RFREQ = 100kΩ) if it is not in dropout (VBATT <
0.88 ×VDCIN). The controller starts a new cycle by turn-
ing on the high-side MOSFET and turning off the low-
side MOSFET. When the charge-current feedback
signal (CSI) is greater than the control point (LVC), the
CCMP comparator output goes high and the controller
initiates the off-time by turning off the high-side MOSFET
and turning on the low-side MOSFET. The operating fre-
quency is governed by the off-time and is dependent
upon VDCIN, VBATT, and RFREQ. See the Setting the
Switching Frequency section for more information.
At the end of the fixed off-time, the controller initiates a
new cycle if the control point (LVC) is greater than
100mV, and the peak charge current is less than the
cycle-by-cycle current limit. Restated another way, IMIN
must be high and IMAX must be low for the controller to
initiate a new cycle. If the peak inductor current exceeds
the IMAX comparator threshold, then the on-time is ter-
minated. The cycle-by-cycle current limit effectively pro-
tects against overcurrent and short-circuit faults.
There is a 0.3µs minimum off-time when the (VDCSNS -
VBATT) differential becomes too small. If VBATT ≥0.88 x
VDCSNS, then the threshold for minimum off-time is
reached and the off-time is fixed at 0.3µs. The switch-
ing frequency in this mode varies according to the
equation:
f =×
V-V
0.3 s V
IN OUT
IN
µ
Simplified Multichemistry
SMBus Battery Charger
16 ___________________________________________________________________________________________________
Figure 5. SMBus Write-Word and Read-Word Protocols
S
a) WRITE-WORD FORMAT
WACK ACK ACK P
COMMAND
BYTE
LOW DATA
BYTE
HIGH DATA
BYTE
SLAVE
ADDRESS ACK
7 BITS 8 BITS1b
MSB LSB MSB LSB
8 BITS
MSB LSB
8 BITS
MSB LSB0
1b
0
1b
0
1b
0
1b
0
PRESET to
0b0001001
ChargingCurrent() = 0x14
ChargerVoltage() = 0x15
D7 D0 D15 D8
S
b) READ-WORD FORMAT
WACK ACK NACK P
COMMAND
BYTE
LOW DATA
BYTE
HIGH DATA
BYTE
SLAVE
ADDRESS SACK
7 BITS 8 BITS1b
MSB LSB
SLAVE
ADDRESS
7 BITS
MSB LSBMSB LSB
8 BITS
MSB LSB
8 BITS
MSB LSB0
1b
0
RACK
1b
1
1b
0
1b
0
1b
0
1b
1
PRESET to
0b0001001
PRESET to
0b0001001
DeviceID() = 0xFF
ManufacturerID() = 0xFE
D7 D0 D15 D8
LEGEND
S = START CONDITION OR REPEATED START CONDITION
ACK = ACKNOWLEDGE (LOGIC LOW)
W = WRITE BIT (LOGIC LOW)
P = STOP CONDITION
NACK = NOT ACKNOWLEDGE (LOGIC HIGH)
R = READ BIT (LOGIC HIGH)
MASTER TO SLAVE
SLAVE TO MASTER
Discontinuous Conduction
The MAX8713 can also operate in discontinuous-con-
duction mode to ensure that the inductor current is
always positive. The MAX8713 enters discontinuous-
conduction mode when the output of the LVC control
point falls below 100mV. For RS = 40mΩ, this corre-
sponds to 62.5mA.
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________________________ 17
Figure 6. SMBUs Write Timing
SMBCLK
AB CD
EFG H
IJK
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tHD:DAT
tHD:DAT tSU:STO tBUF
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
LM
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
Figure 7. SMBus Read Timing
SMBCLK
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
AB CD
EFG H
IJ
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tHD:DAT tSU:DAT tSU:STO tBUF
K
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
Table 4. Battery-Charger Command Summary
COMMAND COMMAND NAME READ/WRITE DESCRIPTION POR STATE
0x14 ChargeCurrent() Write Only 6-Bit Charge Current Setting 0x0000
0x15 ChargeVoltage() Write Only 11-Bit Charge Voltage Setting 0x0000
0xFE ManufacturerID() Read Only Manufacturer ID 0x004D
0xFF DeviceID() Read Only Device ID 0x0007
MAX8713
In discontinuous mode, a new cycle is not started until
the LVC voltage rises above 100mV. Discontinuous-
mode operation can occur during conditioning charge
of overdischarged battery packs or when the charger is
in constant voltage mode as the charge current drops
to zero.
Compensation
The charge voltage and charge current-regulation
loops are compensated separately and independently
at CCV and CCI.
CCV Loop Compensation
The simplified schematic in Figure 9 is sufficient to
describe the operation of the MAX8713 when the volt-
age loop (CCV) is in control. The required compensa-
tion network is a pole-zero pair formed with CCV and
RCV. The pole is necessary to roll off the voltage loop’s
response at low frequency. The zero is necessary to
compensate the pole formed by the output capacitor
and the load. RESR is the equivalent series resistance
(ESR) of the charger output capacitor (COUT). RLis the
equivalent charger output load, where RL= ∆VBATT /
∆ICHG. The equivalent output impedance of the GMV
amplifier, ROGMV, is greater than 10MΩ. The voltage
amplifier transconductance, GMV = 0.125µA/mV. The
DC-DC converter transconductance is dependent upon
the charge current-sense resistor RS:
where ACSI = 20 and RS = 0.04Ωin the typical applica-
tion circuits, so GMOUT = 1.25A/V.
The loop-transfer function is given by:
The poles and zeros of the voltage loop-transfer func-
tion are listed from lowest frequency to highest frequen-
cy in Table 5.
Near crossover, CCV is much lower impedance than
ROGMV. Since CCV is in parallel with ROGMV, CCV domi-
nates the parallel impedance near crossover. Additionally
RCV is much higher impedance than CCV and dominates
the series combination of RCV and CCV, so:
COUT is also much lower impedance than RLnear
crossover, so the parallel impedance is mostly capaci-
tive and:
If RESR is small enough, its associated output zero has
a negligible effect near crossover and the loop-transfer
function can be simplified as follows:
Setting LTF = 1 to solve for the unity-gain frequency
yields:
For stability, choose a crossover frequency less than
1/10 of the switching frequency. For example, choosing
a crossover frequency of 25kHz and solving for RCV
using the component values listed in Figure 1 yields:
RCV = 10kΩ.
VBATT= 8.4V GMV = 0.125mA/mV
ICHG = 2A GMOUT = 1.25A/V
COUT = 10µF fOSC = 400kHz
RL= 0.2ΩfCO_CV = 25kHz
To ensure that the compensation zero adequately can-
cels the output pole, select fZ_CV ≤fP_OUT.
CCV ≥(RL/ RCV) x COUT
CCV ≥200pF (assuming 2 cells and 2A maximum
charge current).
Figure 10 shows the Bode plot of the voltage loop fre-
quency response using the values calculated above.
RCf
GMV GM k
CV OUT CO_CV
OUT
2
=××
×≅
π10 Ω
fGG
R
C
CO_CV OUT MV CV
OUT
M2
=××
×π
LTF G R
CG=××Ms
OUT CV
OUT MV
R
CRC
L
OUT L OUT
(1+ s ) s×≅1
RCR
CR R
OGMV CV CV
CV OGMV CV
(1+ s )
(1+ s )
××
×≅
LTF GM R GMV R
CR CR
CR C R
=××××
××
××
OUT L OGMV
OUT ESR CV CV
CV OGMV OUT L
(1+ s )(1+ s )
(1+ s )(1+ s )
GM S
OUT CSI
1
AR
=×
..
arg
I1
20 R
DIS =×
×=
=
05 00 62 5
40
mV
SmA
ch e current for RS mΩ
Simplified Multichemistry
SMBus Battery Charger
18 ______________________________________________________________________________________
CCI Loop Compensation
The simplified schematic in Figure 11 is sufficient to
describe the operation of the MAX8713 when the bat-
tery current loop (CCI) is in control. Since the output
capacitor’s impedance has little effect on the response
of the current loop, only a simple single pole is required
to compensate this loop. ACSI is the internal gain of the
current-sense amplifier. RS is the charge current-sense
resistor (40mΩ). ROGMI is the equivalent output imped-
ance of the GMI amplifier, which is greater than 10MΩ.
GMI is the charge-current amplifier transconductance
= 1µA/mV. GMOUT is the DC-DC converter transcon-
ductance = 1.25A/V.
The loop-transfer function is given by:
which describes a single-pole system.
the loop-transfer function simplifies to:
The crossover frequency is given by:
For stability, choose a crossover frequency lower than
1/10 of the switching frequency.
CCI > 10 ×GMI / (2πfOSC) = 4nF, for a 400kHz switch-
ing frequency (RFREQ = 100kΩ).
Values for CCI greater than ten times the minimum value
may slow down the current-loop response. Choosing
CCI=10nF yields a crossover frequency of 15.9kHz.
Figure 12 shows the Bode plot of the current-loop fre-
quency response using the values calculated above.
MOSFET Drivers
The DHI and DLO outputs are optimized for driving
moderate-sized power MOSFETs. The MOSFET drive
capability is the same for both the low-side and high-
side switches. This is consistent with the variable duty
factor that occurs in the notebook computer environ-
ment where the battery voltage changes over a wide
range. There must be a low-resistance, low-inductance
path from the DLO driver to the MOSFET gate to pre-
vent shoot-through. Otherwise, the sense circuitry in the
MAX8713 will interpret the MOSFET gate as “off” while
there is still charge left on the gate. Use very short,
wide traces measuring 10 to 20 squares or less
(1.25mm to 2.5mm wide if the MOSFET is 25mm from
the device). Unlike the DLO output, the DHI output uses
a 50ns (typ) delay time to prevent the low-side MOSFET
from turning on until DHI is fully off. The same consider-
ations should be used for routing the DHI signal to the
high-side MOSFET.
fGMI
C
CO_CI CI
=2π
LTF GMI R
sR C
=×
OGMI
OGMI CI
1+
Since GM ARS
OUT CSI
=×
1,
LTF GM A RS GMI R
sR C
=××× ×
OUT CSI OGMI
OGMI CI
1+
,
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________ 19
Figure 8. DC-DC Converter Block Diagram
IMAX
CCMP
IMIN
ZCMP
CSI
2V
100mV
150mV
DCIN
BATT
LVC
R
R
Q
Q
OFF-TIME
ONE-SHOT
OFF-TIME
COMPUTE
TO
DH
DRIVER
TO
DL
DRIVER
Figure 9. CCV Loop Diagram
CCV
COUT
RCV
RLRESR
ROGMV
CCV
BATT
GMV
REF
GMOUT
MAX8713
The high-side driver (DHI) swings from LX to 5V above
LX (BST) and has a typical impedance of 7Ωsourcing
and 2Ωsinking. The low-side driver (DLO) swings from
DLOV to ground and has a typical impedance of 2Ω
sinking and 7Ωsourcing. This helps prevent DLO from
being pulled up when the high-side switch turns on, due
to capacitive coupling from the drain to the gate of the
low-side MOSFET. This places some restrictions on the
MOSFETs that can be used. Using a low-side MOSFET
with smaller gate-to-drain capacitance can prevent
these problems.
Design Procedure
MOSFET Selection
Choose the n-channel MOSFETs according to the maxi-
mum-required charge current. Low-current applications
usually require less attention. The high-side MOSFET
(M1) must be able to dissipate the resistive losses plus
the switching losses at both VDCIN(MIN) and
VDCIN(MAX). Calculate both of these sums.
Ideally, the losses at VDCIN(MIN) should be roughly
equal to the losses at VDCIN(MAX), with lower losses in
between. If the losses at VDCIN(MIN) are significantly
Simplified Multichemistry
SMBus Battery Charger
20 ______________________________________________________________________________________
Table 5. CCV Loop Poles and Zeros
NAME EQUATION DESCRIPTION
CCV Pole
Lowest Frequency Pole Created by CCV and GMV’s Finite Output Resistance.
Since ROGMV is very large and not well controlled, the exact value for the pole
frequency is also not well controlled (ROGMV > 10MΩ).
CCV Zero
Voltage Loop-Compensation Zero. If this zero is at the same frequency or lower
than the output pole fP_OUT, then the loop-transfer function approximates a
single-pole response near the crossover frequency. Choose CCV to place this
zero at least 1 decade below crossover to ensure adequate phase margin.
Output
Pole
Output Pole Formed with the Effective Load Resistance (RL) and the Output
Capacitance (COUT). RL influences the DC gain but does not affect the stability
of the system or the crossover frequency.
Output
Zero
Output ESR Zero. This zero can keep the loop from crossing unity gain if fZ_OUT
is less than the desired crossover frequency; therefore, choose a capacitor with
an ESR zero greater than the crossover frequency.
fRC
P_CV OGMV CV
=×
1
2π
fRC
Z_CV CV CV
=×
1
2π
fRC
P_OUT LOUT
=×
1
2π
fRC
Z_OUT ESR OUT
=×
1
2π
FREQUENCY (Hz)
MAGNITUDE (dB)
100k10k1k100101
-20
0
20
40
60
80
-40
PHASE (DEGREES)
-90
-45
0
-135
01M
MAGNITUDE
PHASE
Figure 10. CCV Loop Response
CCI ROGMI
CCI
GMI
CSI
ICTL
GMOUT
CSIP
RS2
CSIN
Figure 11. CCI Loop Diagram
higher than the losses at VDCIN(MAX), consider increas-
ing the size of M1. Conversely, if the losses at
VDCIN(MAX) are significantly higher than the losses at
VIN(MIN), consider reducing the size of M1. If DCIN
does not vary over a wide range, the minimum power
dissipation occurs where the resistive losses equal the
switching losses. Choose a low-side MOSFET that has
the lowest-possible on-resistance (RDS(ON)), comes in
a moderate-sized package (i.e., one or two 8-pin SO,
DPAK, or D2PAK), and is reasonably priced. Make sure
that the DLO gate driver can supply sufficient current to
support the gate charge and the current injected into
the parasitic gate-to-drain capacitor caused by the
high-side MOSFET turning on; otherwise, cross-con-
duction problems can occur. Select devices that have
short turn-off times, and make sure that M2(tDOFF(MAX))
- M1(tDON(MIN)) < 30ns, and M1(tDOFF(MAX)) -
M2(tDON(MIN)) < 30ns. Failure to do so may result in
efficiency-killing shoot-through currents.
MOSFET Power Dissipation
Worst-case conduction losses occur at the duty-factor
extremes. For the high-side MOSFET, the worst-case
power dissipation (PD) due to resistance occurs at the
minimum supply voltage:
Generally, a small high-side MOSFET is desired to
reduce switching losses at high input voltages.
However, the RDS(ON) required to stay within package
power-dissipation limits often limits how small the
MOSFET can be. The optimum occurs when the switch-
ing (AC) losses equal the conduction (RDS(ON)) losses.
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum AC adapter
voltages are applied, due to the squared term in the
CV2f switching-loss equation. If the high-side MOSFET
that was chosen for adequate RDS(ON) at low supply
voltages becomes extraordinarily hot when subjected
to VIN(MAX), then choose a MOSFET with lower losses.
Calculating the power dissipation in M1 due to switch-
ing losses is difficult since it must allow for difficult
quantifying factors that influence the turn-on and turn-
off times. These factors include the internal gate resis-
tance, gate charge, threshold voltage, source
inductance, and PC board layout characteristics. The
following switching-loss calculation provides only a
very rough estimate and is no substitute for breadboard
evaluation, preferably including a verification using a
thermocouple mounted on M1:
where CRSS is the reverse transfer capacitance of M1,
and IGATE is the peak gate-drive source/sink current
(0.7A sourcing and 2.5A sinking).
For the low-side MOSFET (M2), the worst-case power
dissipation always occurs at maximum input voltage:
PD R
(LOW-SIDE) BATT
DCIN
LOAD DS(ON)
-V
V
I
2
2
=
×1
PD(HS_SWITCHING) DCIN(MAX) RSS SW LOAD
GATE
VCfI
2I
2
=×××
×
PD R
(HIGH-SIDE) BATT
DCIN
LOAD DS(ON)
V
V
I
2
2
=
×
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________ 21
FREQUENCY (Hz)
MAGNITUDE (dB)
100k10k1k
-10
0
10
20
30
40
50
60
-20
PHASE (DEGREES)
-45
0
-90
100 1M
MAGNITUDE
PHASE
Figure 12. CCI Loop Response
BATTERY VOLTAGE (V)
RIPPLE CURRENT (A)
1082 4 6
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0
012
VADAPTER = 12V
Figure 13. Ripple Current vs. Battery Voltage
MAX8713
Inductor Selection
The charge current, ripple, and operating frequency
(off-time) determine the inductor characteristics. For
optimum efficiency, choose the inductance according
to the following equation:
L = VBATT ×tOFF / (0.3 x ICHG)
This sets the ripple current to 1/3 of the charge current
and results in a good balance between inductor size
and efficiency. Higher inductor values decrease the
ripple current. Smaller inductor values require high sat-
uration current capabilities and degrade efficiency.
Inductor L1 must have a saturation current rating of at
least the maximum charge current plus 1/2 of the ripple
current (∆IL):
ISAT = ICHG + (1/2) ∆IL
The ripple current is determined by:
∆IL = VBATT ×tOFF / L
where tOFF = 2.5µs (VDCIN - VBATT) / VDCIN for VBATT <
0.88 VDCIN, or:
tOFF = 0.3µs for VBATT > 0.88 VDCIN.
Figure 13 illustrates the variation of the ripple current
vs. battery voltage when the circuit is charging at 2A
with a fixed input voltage of 19V.
Input Capacitor Selection
The input capacitor must meet the ripple-current
requirement (IRMS) imposed by the switching currents.
Nontantalum chemistries (ceramic, aluminum, or
OS-CON) are preferred due to their resilience to power-
up surge currents.
The input capacitors should be sized so that the tem-
perature rise due to ripple current in continuous con-
duction does not exceed approximately +10°C. The
maximum ripple current occurs at 50% duty factor or
VDCIN = 2 x VBATT, which equates to 0.5 x ICHG. If the
application of interest does not achieve the maximum
value, size the input capacitors according to the worst-
case conditions.
Output Capacitor Selection
The output capacitor absorbs the inductor ripple cur-
rent and must tolerate the surge current delivered from
the battery when it is initially plugged into the charger.
As such, both capacitance and ESR are important
parameters in specifying the output capacitor as a filter
and to ensure the stability of the DC-DC converter (see
the Compensation section). Beyond the stability require-
ments, it is often sufficient to make sure that the output
capacitor’s ESR is simply much lower than the battery’s
ESR. Either tantalum or ceramic capacitors can be
used on the output. Ceramic devices are preferable
because of their good voltage ratings and resilience to
surge currents.
Applications Information
Layout and Bypassing
Bypass DCIN with a 0.1µF ceramic to ground (Figure
1). D1 and D2 protect the MAX8713 when the DC
power source input is reversed. A signal diode for D2 is
adequate because DCIN only powers the LDO and the
internal reference. Bypass VDD, DCIN, LDO, DHIV,
DLOV, SRC, DAC, and REF as shown in Figure 1.
Good PC board layout is required to achieve specified
noise immunity, efficiency, and stable performance.
The PC board layout artist must be given explicit
instructions—preferably, a sketch showing the place-
ment of the power switching components and high-cur-
rent routing. Refer to the PC board layout in the
MAX8713 evaluation kit for examples. A ground plane
is essential for optimum performance. In most applica-
tions, the circuit is located on a multilayer board, and
full use of the four or more copper layers is recom-
mended. Use the top layer for high-current connec-
tions, the bottom layer for quiet connections, and the
inner layers for uninterrupted ground planes.
Use the following step-by-step guide:
1) Place the high-power connections first, with their
grounds adjacent:
•Minimize the current-sense resistor trace lengths,
and ensure accurate current sensing with Kelvin
connections.
•Minimize ground trace lengths in the high-current
paths.
•Minimize other trace lengths in the high-current
paths.
•Use >5mm-wide traces in the high-current paths.
•Connect C1 and C2 to the high-side MOSFET
(10mm max length).
•Minimize the LX node (MOSFETs, rectifier cathode,
inductor (15mm max length)). Keep LX on one side
of the PC board to reduce EMI radiation.
()
II
RMS CHG BATT DCIN BATT
DCIN
VV-V
V
=
Simplified Multichemistry
SMBus Battery Charger
22 ______________________________________________________________________________________
Ideally, surface-mount power components are flush
against one another with their ground terminals
almost touching. These high-current grounds are
then connected to each other with a wide, filled
zone of top-layer copper, so they do not go through
vias. The resulting top-layer subground plane is
connected to the normal inner-layer ground plane
at the paddle. Other high-current paths should also
be minimized, but focusing primarily on short
ground and current-sense connections eliminates
about 90% of all PC board layout problems.
2) Place the IC and signal components. Keep the
main switching node (LX node) away from sensitive
analog components (current-sense traces and REF
capacitor). Note: The IC must be no further than
10mm from the current-sense resistors. Quiet con-
nections to REF, VMAX, IMAX, CCV, CCI, ACIN,
and DCIN should be returned to a separate ground
(GND) island. The appropriate traces are marked
on the schematic with the () ground symbol. There
is very little current flowing in these traces, so the
ground island need not be very large. When placed
on an inner layer, a sizable ground island can help
simplify the layout because the low-current connec-
tions can be made through vias. The ground pad
on the backside of the package should also be
connected to this quiet ground island.
3) Keep the gate-drive traces (DHI and DLO) as short
as possible (L < 20mm), and route them away from
the current-sense lines and REF. These traces
should also be relatively wide (W > 1.25mm).
4) Place ceramic bypass capacitors close to the IC.
The bulk capacitors can be placed further away.
Place the current-sense input filter capacitors under
the part, connected directly to the GND pin.
5) Use a single-point star ground placed directly
below the part at the PGND pin. Connect the power
ground (ground plane) and the quiet ground island
at this location.
Chip Information
TRANSISTOR COUNT: 8400
PROCESS: BiCMOS
MAX8713
Simplified Multichemistry
SMBus Battery Charger
______________________________________________________________________________________ 23
MAX8713
Simplified Multichemistry
SMBus Battery Charger
24 ______________________________________________________________________________________
24L QFN THIN.EPS
C
1
2
21-0139
PACKAGE OUTLINE
12, 16, 20, 24L THIN QFN, 4x4x0.8mm
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX8713
Simplified Multichemistry
SMBus Battery Charger
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 25
©2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
C
2
2
21-0139
PACKAGE OUTLINE
12, 16, 20, 24L THIN QFN, 4x4x0.8mm
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
