MAX1640 Datasheet, PDF (8/11 Pages) Maxim Integrated Products – Adjustable-Output, Switch-Mode Current Sources with Synchronous Rectifier

Adjustable-Output, Switch-Mode
Current Source with Synchronous Rectifier
The voltage at SET is given by:
R1 = R2 (V_REF / V_SET -1 ); 10kΩ < R2 < 300kΩ
where V_REF = 2V and V_SET is proportional to the
desired output current level.
Table 1. Selecting Output Current Levels
D1 DO
00
01
10
MODE
OFF
Top-Off
Pulse-Trickle
OUTPUT CURRENT (A)
0
V_SET / (13.3R_SENSE)
V_SET / (13.3R_SENSE)
12.5% duty cycle
1 1 Fast Charge V_SET / (13.3R_SENSE)
L
MAX1641
CS+
CS-
TERM
BATT
R3
R_SENSE
R4
Figure 4b. Setting the Maximum Output Voltage Level
MAX1640
MAX1641
REF
R1
SET
R2
The MAX1640/MAX1641 are specified for V_SET
between 0V and V_REF. For V_SET > V_REF, output current
increases linearly (with reduced accuracy) until it
clamps at V_SET ≈ 4V.
Pulse-Trickle Mode: Selecting the
Pulse-Trickle Current
Pulling D0 low and D1 high selects pulse-trickle mode.
This current equals V_SET / (13.3R_SENSE) and remains
on for 12.5% of the period set by R_TOFF. Pulse-trickle
current maintains full charge across the battery and
can slowly charge a cold battery before fast charging
commences.
Figure 3. Adjusting the Output Current Level
PERIOD = 3.2 x 10^-7 x R_TOFF(sec)
MAX1640
CS+
CS-
TERM
L
R_SENSE
R3
BATT
R4
Figure 4a. Setting the Maximum Output Voltage Level
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
a level higher than the output/battery voltage (I_LOAD x
R_LOAD). An external resistor-divider between the output
and ground (Figure 4) 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 10kΩ to 500kΩ range.
R3 is given by:
R3 = R4 (V_OUT / V_TERM) -1
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