MAX8731 Maxim Integrated Products, MAX8731 Datasheet - Page 14

• Manufacturer Part Number: MAX8731
• Description: SMBus Level 2 Battery Charger
• Manufacturer: Maxim Integrated Products

SMBus Level 2 Battery Charger with
Remote Sense
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
Figure 1. Typical Dual-Battery Application Circuit
14
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ADAPTER
INPUT
Detailed Description
KBC
1µF
INPUT
D1
C1
VDD
SDA
SCL
0.01µF
49.9kΩ
150kΩ
10kΩ
10kΩ
LDO
C4
R3
R1
R5
R8
10kΩ
10kΩ
R4
R7
10kΩ
R6
N
0.01µF
0.1µF
0.1µF
C6
0.01µF
C2
C3
C5
100kΩ
C7
1µF
R2
DCIN
ACIN
ACOK
V
SCL
SDA
IINP
CCV
CCI
CCS
REF
DD
DAC
MAX8731
C8
0.1µF
BP
BATSEL
PGND
CSSP
CSSN
FBSB
FBSA
GND
CSIP
CSIN
LDO
DLO
V
BST
DHI
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
current limit set by the ChargeCurrent() command. The
LX
CC
100Ω
100Ω
LDO
R10
D2
R9
C10
0.1µF
C12
1µF
D3
R13
1kΩ
C9
220pF
R11
1Ω
R12
33Ω
N1
C11
1µF
LDO
BATTERY
SELECTOR
A
N3
RS1
10mΩ
N1, N2,: SI4800BDY
N3: SI4810BDY
C
10µF
DHI
IN1
RS2
10mΩ
L1
4.3µH
L1: SUMIDA
CEP125-4R3MC-U
BATTERY
B
V
C
10µF
OUT
OUT1
SYSTEM
C
10µF
N2
LOAD
IN2
C
10µF
OUT2