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MAX1640_09 Datasheet, PDF (7/12 Pages) Maxim Integrated Products – Adjustable-Output, Switch-Mode Current Sources with Synchronous Rectifier
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Adjustable-Output, Switch-Mode
Current Source with Synchronous Rectifier
47μF
4.7μF
0.1μF
RTOFF
R1
0.1μF
R2
IN
LDOL
0.33μF
LDOH
PDRV
1/2 IR7309
P
MAX1641
D0
D1
TOFF
1/2 IR7309
NDRV
N
REF
PGND
47μH
VOUT
BATT
R3
CS+
SET
CS-
100mΩ
R4
CC
0.01μF
TERM
GND
47μF
0.33μF
4.7μF
0.1μF
RTOFF
IN
LDOL
LDOH
PDRV
1/2 IR7309
P
MAX1640
D0
D1
TOFF
1/2 IR7309
NDRV
N
REF
PGND
47μH
R1
0.1μF
R2
CS+
SET
CS-
R3
TERM
CC GND
R4
0.01μF
100mΩ
VOUT
BATT
Figure 1a. Standard Application Circuit
Figure 1b. Standard Application Circuit
_______________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.
See the Functional Diagram. Figures 1a and 1b show
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 2).
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