19-3923; Rev 0; 1/06
KIT
ATION
EVALU
BLE
AVAILA
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 10mΩ sense 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.
SMBus is a trademark of Intel Corp.
Features
♦
♦
♦
♦
♦
0.5% Battery Voltage Accuracy
3% Input Current-Limit Accuracy
3% Charge-Current Accuracy
SMBus 2-Wire Serial Interface
Cycle-by-Cycle Current Limit
Battery Short-Circuit Protection
Fast Response for Pulse Charging
Fast System-Load-Transient Response
Dual-Remote-Sense Inputs
Monitor Outputs for
Adapter Current (4% Accuracy)
AC Adapter Detection
11-Bit Battery Voltage Setting
6-Bit Charge-Current/Input-Current Setting
8A (max) Battery Charger Current
11A (max) Input Current
+8V to +26V Input Voltage Range
Charges Li+, NiMH, and NiCd Battery Chemistries
MAX8731
♦
♦
♦
♦
♦
♦
♦
♦
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
28 Thin QFN (5mm x 5mm)
MAX8731ETI+ -40°C to +85°C
+Indicates
lead-free packaging.
Applications
Notebook Computers
Tablet PCs
Medical Devices
Portable Equipment with Rechargeable Batteries
Typical Operating Circuit
EXTERNAL
LOAD
OPTIONAL
CSSP
CSSN
DHI
LX
Pin Configuration
PGND
FBSB
FBSA
CSIN
CSIP
LDO
DLO
N
TOP VIEW
ACIN
DCIN
ACOK
MAX8731
DLO
REF
PGND
BST
CSIP
CSIN
N
21
DCIN 22
LX 23
DHI 24
BST 25
V
CC
26
CSSN 27
CSSP 28
1
GND
20
19
18
17
16
15
14
13
12
BATSEL
ACOK
GND
V
DD
SCL
SDA
IINP
HOST
SCL
SDA
VDD
GND
SELECTOR
FBSA
BATSEL
SCL
SDA
V
DD
GND
IINP
DAC CCS
LDO
V
CC
CCV
CCI
FBSB
BATSEL
BATTERY
A
MAX8731
11
10
*EXPOSED PADDLE
9
8
BATTERY
B
2
ACIN
3
REF
4
CCS
5
CCI
6
CCV
7
DAC
THIN QFN
5mm x 5mm
________________________________________________________________
Maxim Integrated Products
1
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.
SMBus Level 2 Battery Charger with
Remote Sense
MAX8731
ABSOLUTE MAXIMUM RATINGS
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 +(V
BST
+ 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 (V
VCC
+ 0.3)V
V
DD
, SCL, SDA, BATSEL, ACIN, ACOK, V
CC
to GND,
LDO to PGND ......................................................-0.3V to +6V
Continuous Power Dissipation (T
A
= +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
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.
ELECTRICAL CHARACTERISTICS
(V
DCIN
= V
LX
= V
CSSP
= V
CSSN
= 19V, V
BST
- V
LX
= 4.5V, V
FBSA
= V
FBSB
= V
CSIP
= V
CSIN
= 16.8V, BATSEL = GND = PGND = 0,
C
LDO
= 1µF, V
CC
= LDO, C
REF
= 1µF, C
DAC
= 0.1µF, V
DD
= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1;
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
CHARGE-VOLTAGE REGULATION
ChargingVoltage() = 0x41A0
ChargingVoltage() = 0x3130
Battery Full-Charge Voltage and
Accuracy
ChargingVoltage() = 0x20D0
ChargingVoltage() = 0x1060
Battery Undervoltage-Lockout
Trip Point for Trickle Charge
CHARGE-CURRENT REGULATION
CSIP to CSIN Full-Scale Current-
Sense Voltage
RS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x1f80
Charge Current and Accuracy
RS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x0f80
RS2 (Figure 1) = 10mΩ;
ChargingCurrent() = 0x0080 (128mA)
Charge-Current Gain Error
FBSA/FBSB/CSIP/CSIN
Input Voltage Range
Based on ChargeCurrent() = 128mA and 8.064A
78.22
7.822
-3
3.809
-4
64
-2
0
3.968
80.64
8.064
83.06
8.306
+3
4.126
+4
400
+2
19
mV
A
%
A
%
mA
%
V
16.716
-0.5
12.491
-0.8
8.333
-0.8
4.15
-1.0
2.5
4.192
8.4
12.592
16.8
16.884
+0.5
12.693
+0.8
8.467
+0.8
4.234
+1.0
V
%
V
%
V
%
V
%
V
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= V
LX
= V
CSSP
= V
CSSN
= 19V, V
BST
- V
LX
= 4.5V, V
FBSA
= V
FBSB
= V
CSIP
= V
CSIN
= 16.8V, BATSEL = GND = PGND = 0,
C
LDO
= 1µF, V
CC
= LDO, C
REF
= 1µF, C
DAC
= 0.1µF, V
DD
= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1;
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
CONDITIONS
Adapter present, not charging, I
CSIP
+ I
CSIN
+ I
LX
+ I
FBS,
V
FBS_
= V
LX
= V
CSIN
= V
CSIP
= 19V
Adapter absent, I
CSIP
+ I
CSIN
+ I
LX
+ I
FBSA
+ I
FBSB
+ I
CSSP
+ I
CSSN
, V
FBS_
= V
LX
= V
CSIN
= V
CSIP
= 19V, V
DCIN
= 0V
V
Adapter
= 26V, V
Battery
= 16.8V, not
charging
Adapter Quiescent Current
I
DCIN
+
I
CSSP
+
I
CSSN
V
Adapter
= 19V,
V
Battery
= 16.8V
V
Adapter
= 8V,
V
Battery
= 4V
INPUT-CURRENT REGULATION
CSSP to CSSN Full-Scale
Current-Sense Voltage
Input Current Accuracy
POR Input Current
Input Current-Limit Gain Error
Input Current-Limit Offset
CSSP/CSSN Input Voltage Range
IINP Transconductance
IINP Offset
IINP Accuracy
IINP Output Voltage Range
SUPPLY AND LINEAR REGULATOR
DCIN, Input Voltage Range
DCIN Undervoltage-Lockout
Trip Point
Power-Fail Threshold
DCIN falling
DCIN rising
V
CSSP
- V
CSIN
falling
V
CSSP
- V
CSIN
rising
9
160
8.0
7
7.4
7.5
15
210
7.85
21
271
26.0
V
V
mV
V
CSSP - CSSN
= 110mV
Based on V
CSSP - CSSN
= 110mV and 20mV
V
CSSP - CSSN
= 110mV
V
CSSP - CSSN
= 55mV or 35mV
V
CSSP - CSSN
= 20mV
VFBS_ = 19V
RS1 (Figure 1) = 10mΩ, InputCurrent() = 11004mA or
3584mA
RS1 (Figure 1) = 10mΩ, InputCurrent() = 2048mA
RS1 (Figure 1) = 10mΩ
Based on InputCurrent() = 1024mA and 11004mA
-2
-1
8
2.85
-1.5
-5
-4
-10
0
3.0
106.7
-3
-5
256
+2
+1
26
3.15
+1.5
+5
+4
+10
3.5
V
%
110
113.3
+3
+5
mV
%
%
mA
%
mV
V
mA/V
mV
Charging
Not charging
Charging
Not charging
200
0.4
200
0.4
200
MIN
TYP
2
MAX
5
µA
+1
500
1
500
1
500
µA
mA
µA
mA
µA
UNITS
MAX8731
Battery Quiescent Current
_______________________________________________________________________________________
3
SMBus Level 2 Battery Charger with
Remote Sense
MAX8731
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= V
LX
= V
CSSP
= V
CSSN
= 19V, V
BST
- V
LX
= 4.5V, V
FBSA
= V
FBSB
= V
CSIP
= V
CSIN
= 16.8V, BATSEL = GND = PGND = 0,
C
LDO
= 1µF, V
CC
= LDO, C
REF
= 1µF, C
DAC
= 0.1µF, V
DD
= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1;
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
LDO Output Voltage
LDO Load Regulation
LDO Undervoltage-Lockout Threshold
V
DD
Range
V
DD
UVLO Rising
V
DD
UVLO Hysteresis
V
DD
Quiescent Current
REFERENCE
REF Output Voltage
REF Undervoltage-Lockout Trip Point
ACOK
ACOK Sink Current
ACOK Leakage Current
ACIN
ACIN Threshold
ACIN Threshold Hysteresis
ACIN Input Bias Current
REMOTE-SENSE INPUTS
FBS_ Range
FBS_ Gain
CSIN-FBS_ Clamp Voltage
FBS_ Bias Current
FBS_ Bias Current
SWITCHING REGULATOR
Off-Time
BST Supply Current
LX Input Bias Current
Maximum Discontinuous-Mode Peak
Current (I
MIN
)
DHI On-Resistance Low
DHI On-Resistance High
DLO On-Resistance High
DLO On-Resistance Low
I
DHI
= -10mA
I
DHI
= 10mA
I
DLO
= 10mA
I
DLO
= -10mA
V
CSIN
= 16.0V, V
CSSP
= 19V
V
CSIN
= 16.0V, V
CSSP
= 17V
DHI high
V
DCIN
= 28V, V
CSIN
= V
LX
= 20V, DHI low
0.5
1
3
3
1
3
5
5
3
360
260
400
300
500
440
360
800
2
ns
µA
µA
A
Ω
Ω
Ω
Ω
Charger switching, FBS_ selected
Charger not switching or FBS_ not selected
-2
V
CSIN
- V
FBS
∆V
CSIN
/
∆(V
CSIN
- V
FBS_
)
0
0.95
225
1.00
250
200
1.05
275
14
+2
mV
V/V
mV
µA
µA
2.007
10
-1
2.048
20
2.089
30
+1
V
mV
µA
V
ACOK
= 0.4V, ACIN = 1.5V
V
ACOK
= 5.5V, ACIN = 2.5V
1
1
mA
µA
0 < I
REF
< 500µA
REF falling
4.071
4.096
3.1
4.120
3.9
V
V
DCIN < 6V, V
DD
= 5.5V, SCL = SDA = 5.5V
0 < I
LDO
< 30mA
V
DCIN
= 8.0V, V
LDO
falling
3.20
2.7
2.5
100
16
27
CONDITIONS
8.0V < V
DCIN
< 28V, no load
MIN
5.25
TYP
5.4
34
4
MAX
5.55
100
5.15
5.5
2.7
UNITS
V
mV
V
V
V
mV
µA
4
_______________________________________________________________________________________
SMBus Level 2 Battery Charger with
Remote Sense
ELECTRICAL CHARACTERISTICS (continued)
(V
DCIN
= V
LX
= V
CSSP
= V
CSSN
= 19V, V
BST
- V
LX
= 4.5V, V
FBSA
= V
FBSB
= V
CSIP
= V
CSIN
= 16.8V, BATSEL = GND = PGND = 0,
C
LDO
= 1µF, V
CC
= LDO, C
REF
= 1µF, C
DAC
= 0.1µF, V
DD
= 3.3V, ACIN = 2.5V; pins CCI, CCV, and CCS are compensated per
Figure 1;
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
ERROR AMPLIFIERS
GMV Amplifier Transconductance ChargingVoltage() = 16.8V, V
FBS_
= 16.8V
GMI Amplifier Transconductance
CCI/CCS/CCV Clamp Voltage
LOGIC LEVELS
SDA/SCL Input Low Voltage
SDA/SCL Input High Voltage
SDA/SCL Input Bias Current
BATSEL Input Low Voltage
BATSEL Input High Voltage
BATSEL Input Bias Current
SDA, Output Sink Current
PARAMETERS
SMBus Frequency
Bus Free Time
Start Condition Hold Time from
SCL
Start Condition Setup Time from
SCL
Stop Condition Setup Time from
SCL
SDA Hold Time from SCL
SDA Setup Time from SCL
SCL Low Timeout
SCL Low Period
SCL High Period
Maximum Charging Period
Without a ChargeVoltage() or
ChargeCurrent() Command
V
(SDA)
= 0.4V
SYMBOL
f
SMB
t
BUF
t
HD:STA
t
SU:STA
t
SU:STO
t
HD:DAT
t
SU:DAT
t
TIMEOUT
T
LOW
T
HIGH
(Note 1)
CONDITIONS
SMBus TIMING SPECIFICATIONS (V
DD
= 2.7V to 5.5V) (see Figures 4 and 5)
MIN
10
4.7
4
4.7
4
300
250
25
4.7
4
140
175
210
35
TYP
MAX
100
UNITS
kHz
µs
µs
µs
µs
ns
ns
ms
µs
µs
s
2.1
-1
6
+1
V
DD
= 2.7V to 5.5V
V
DD
= 2.7V to 5.5V
V
DD
= 2.7V to 5.5V
2.1
-1
+1
0.8
0.8
V
V
µA
V
V
µA
mA
ChargingCurrent() = 3968mA, V
CSIP
- V
CSIN
= 39.68mV
0.25V < V
CCI/S/V
< 2.0V
GMS Amplifier Transconductance InputCurrent() = 3968mA, V
CSSP
- V
CSSN
= 79.36mV
0.0625
0.5
0.5
120
0.125
1
1
250
0.2500
2.0
2.0
600
mA/V
mA/V
mA/V
mV
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8731
_______________________________________________________________________________________
5
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