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MB39A104
■ SETTING THE SOFT-START AND DISCHARGE TIMES
To prevent rush currents when the IC is turned on, you can set a soft-start by connecting soft-start capacitors
(C
and C
) to the CS1 terminal (pin 11) for channel 1 and the CS2 terminal (pin 14) for channel 2, respectively.
S1
S2
When CTL terminal (pin 24) goes to "H" level and IC starts (V
start capacitors (C
S1
output (FB1 (pin 9) , FB2 (pin 16) ) is determined by comparison between the lower one of the potentials at two
non-inverted input terminals (1.24 V, CS1 terminal voltages) and the inverted input terminal voltage (−INE1 (pin
10) voltage, −INE2 (pin 15) voltage).
The FB1 (FB2) terminal voltage is decided for the soft-start period by the comparison between 1.24 V in an
internal reference voltage and the voltages of the CS1 (CS2) terminal. The DC/DC converter output voltage
rises in proportion to the CS1 (CS2) terminal voltage as the soft-start capacitor connected to the CS1 (CS2)
terminal is charged.
The soft-start time is obtained from the following formula:
Soft-start time: ts (time to output 100%)
ts (s) : = 0.124 × C
: = 5 V
: = 1.24 V
: = 0 V
14
) connected to CS1 and CS2 terminals are charged at 10 µA. The error amplifier
and C
S2
(µF)
S
Soft-start time (ts)
≥ UVLO threshold voltage), the external soft-
CC
CS1 (CS2) terminal voltage
Error Amp block −INE1 (−INE2) voltage
t
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