Stand-Alone Switch-Mode

Lithium-Ion Battery-Charger Controller

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9

Detailed Description

The MAX1737 includes all of the functions necessary to

charge between one and four series Li+ battery cells. It

includes a high-efficiency synchronous-rectified step-

down DC-DC converter that controls charging voltage

and current. It also includes input source-current limit-

ing, battery temperature monitoring, battery undervolt-

age precharging, battery fault indication, and a state

machine with timers for charge termination.

The DC-DC converter uses an external dual N-channel

MOSFET as a switch and a synchronous rectifier to

convert the input voltage to the charging current or volt-

age. The typical application circuit is shown in Figure 1.

Figure 2 shows a typical charging sequence and

Figure 3 shows the block diagram. Charging current is

set by the voltage at ISETOUT and the voltage across

R18. The battery voltage is measured at the BATT pin.

The battery regulation voltage is set to 4.2V per cell

and can be adjusted ±5% by changing the voltage at

the VADJ pin. By limiting the adjust range, the voltage

27

26

22

23

25

24

21

20

19

7

4

28

CSSP

DCIN

CSSN

VLO

BST

DHI

LX

DLO

PGND

CS

BATT

THM

REF

ISETIN

VL

SHDN

ISETOUT

VADJ

CELL

GND

CCV

CCI

CCS

TIMER1

TIMER2

R12

Li+

BATTERY

(1 TO 4 CELLS)

L1

R18

22

µH

FAULT

FULLCHG

FULL CHARGE

FAST CHARGE

FAULT

FASTCHG

C6

47nF

C13

1nF

C14

1nF

1nF

C5

47nF

C4

C3

1

µF

C1

4.7

µF

C18

22

µF

C19

22

µF

SYSTEM

LOAD

INPUT

SUPPLY

C2

0.1

µF

C7

0.1

µF

C8

0.1

µF

R1

10k

R8

D1

D3

D2

R9

0.1

µF

16

11

9

6

12

3

8

2

5

18

1

10

13

14

17

15

0.1

µF

0.1

µF

C15

68

µF

C9

0.1

µF

C11

0.1

µF

C10

0.1

µF

MAX1737

+

+

THERMISTOR

Figure 1. Typical Application Circuit