MB39A112 Datasheet, PDF (14/35 Pages) Fujitsu Component Limited. – 3-ch DC/DC Converter IC

MB39A112
s 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
(CS1, CS2 and CS3) to the CS1 terminal (pin 1) for channel 1, CS2 terminal (pin 10) for channel 2 and CS3 terminal
(pin 11) for channel 3 respectively.
Setting each control terminal (CTLX) from “H” to “L” starts charging the external soft-start capacitors (CS1, CS2
and CS3) connected to the CS1, CS2 and CS3 terminal at about 10 µA. The DC/DC converter output voltage
rises in proportion to the CS terminal voltage. Also, soft-start time is obtained by the following formulas.
Soft-start time : ts (time to output 100%)
CH1 : ts1[s] =: 0.100 × CS1[µF]
CH2 : ts2[s] =: 0.123 × CS2[µF]
CH3 : ts3[s] =: 0.123 × CS3[µF]
• Soft-start circuit
VO
CH1 ON/OFF signal
(L : ON, H : OFF)
CTLX
−INE1
(−INE2)
(−INE3)
CS1
(CS2)
(CS3)
VREF
10 µA
FB1
(FB2)
(FB3)
L
priority
Error
− ^Amp
++
1.23 V
/1.0 V
H : at SCP
SCP
H: UVLO release
UVLO
• Soft-start operation
=: 3.4 V
=: 1.23 V/
1.00 V
=: 0 V
H
CTLX signal
L
Soft-start time ts
14
CS terminal voltage
Error Amp. reference voltage
t
t