The voltage at SET is given by:

Ω < R2 < 300kΩ

desired output current level.

increases linearly (with reduced accuracy) until it

≈ 4V.

Pulse-Trickle Mode: Selecting the

Pulse-Trickle Current

Pulling D0 low and D1 high selects pulse-trickle mode.

current maintains full charge across the battery and

can slowly charge a cold battery before fast charging

commences.

Off Mode: Turning Off the Output Current

Pulling D0 and D1 low turns off the P-channel FET and

hence the output current flow. This mode also controls

end of charge and protects the battery against exces-

sive temperatures.

Setting the Maximum Output

Voltage Level

The maximum output voltage should be programmed to

and ground (Figure 3) sets the voltage at TERM. Once

the voltage at TERM exceeds the reference, the internal

comparator turns off the P-channel FET, terminating

current flow. Select R4 in the 10k

Ω to 500kΩ range.

R3 is given by:

PERIOD = 3.2 x 10

x R

(sec)

-7

TOFF

Adjustable-Output, Switch-Mode

Current Source with Synchronous Rectifier

8

_______________________________________________________________________________________

D1

DO

MODE

OUTPUT CURRENT (A)

0

0

OFF

0

0

1

Top-Off

1

0

Pulse-Trickle

12.5% duty cycle

1

1

Fast Charge

Table 1. Selecting Output Current Levels

MAX1640

MAX1641

REF

SET

R1

R2

Figure 2. Adjusting the Output Current Level

MAX1640

CS+

TERM

CS-

R3

BATT

L

R4

Figure 3a. Setting the Maximum Output Voltage Level

MAX1641

CS+

TERM

CS-

R3

BATT

R4

L

Figure 3b. Setting the Maximum Output Voltage Level