Adjustable-Output, Switch-Mode

Current Source with Synchronous Rectifier

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7

_______________Detailed Description

The MAX1640/MAX1641 switch-mode current sources

utilize a hysteretic, current-mode, step-down pulse-

width-modulation (PWM) topology with constant off-

time. Internal comparators control the switching

mechanism. These comparators monitor the current

TERM. When inductor current reaches the current limit

and the N-channel FET synchronous rectifier turns on.

Inductor energy is delivered to the load as the current

inductor values. When off-time expires, the P-channel

FET turns back on and the N-channel FET turns off.

Two digital inputs, D0 and D1, select between four pos-

sible current levels (Table 1). In pulse-trickle mode, the

resulting in a lower current for pulse-trickle charging.

See the Functional Diagram. Figures 1a and 1b show

the standard application circuits.

Charge Mode: Programming the

Output Currents

levels. Choose between these two levels by holding

D0 high, and toggling D1 either high or low (Table 1).

grams the voltage at SET (Figure 2).

P

N

0.1

μF

4.7

μF

47

μF

0.33

μF

0.01

μF

0.1

μF

R1

R2

SET

REF

TOFF

D1

D0

LDOL

PDRV

NDRV

PGND

CS+

CS-

TERM

GND

CC

R3

47

μH

BATT

1/2 IR7309

1/2 IR7309

R4

100m

Ω

LDOH

IN

MAX1641

P

N

0.1

μF

0.01

μF

4.7

μF

47

μF

0.33

μF

0.1

μF

R1

R2

SET

REF

TOFF

D1

D0

LDOL

PDRV

NDRV

PGND

CS+

CS-

R3

R4

TERM

GND

CC

47

μH

1/2 IR7309

1/2 IR7309

100m

Ω

BATT

LDOH

IN

MAX1640

Figure 1a. Standard Application Circuit

Figure 1b. Standard Application Circuit