MAX1641EEE datasheet(7/11 Pages) MAXIM

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Adjustable-Output, Switch-Mode

Current Source with Synchronous Rectifier

_______________________________________________________________________________________

_______________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

through a sense resistor (RSENSE) and the voltage at

TERM. When inductor current reaches the current limit

[(VCS+ - VCS-) / RSENSE], the P-channel FET turns off

and the N-channel FET synchronous rectifier turns on.

Inductor energy is delivered to the load as the current

ramps down. This ramp rate depends on RTOFF and

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

part operates for 12.5% of the period set by RTOFF,

resulting in a lower current for pulse-trickle charging.

Figure 1 is the MAX1640/MAX1641 functional diagram.

Figure 2 shows the standard application circuits.

Charge Mode: Programming the

Output Currents

The sense resistor, RSENSE, sets two charging current

levels. Choose between these two levels by holding

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

The fast-charge current level equals VCS / RSENSE

where VCS is the full-scale current-sense voltage of

150mV. Alternatively, calculate this current by VREF /

(13.3RSENSE). The top-off current equals VSET /

(13.3RSENSE). A resistor-divider from REF to GND pro-

grams the voltage at SET (Figure 3).

0.1

µF

4.7

µF

0.33

µF

0.01

µF

0.1

µF

RTOFF

SET

REF

TOFF

LDOL

PDRV

NDRV

PGND

CS+

CS-

TERM

GND

µH

VOUT

BATT

1/2 IR7309

100m

Ω

LDOH

MAX1641

0.1

µF

0.01

µF

4.7

µF

0.33

µF

0.1

µF

SET

REF

TOFF

LDOL

PDRV

NDRV

PGND

CS+

CS-

TERM

GND

µH

1/2 IR7309

100m

Ω

BATT

VOUT

RTOFF

LDOH

MAX1640

Figure 2a. Standard Application Circuit

Figure 2b. Standard Application Circuit

MAX1641EEE Datasheet(PDF) 7 Page - Maxim Integrated Products

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