MB3825A Fujitsu Microelectronics, Inc., MB3825A Datasheet - Page 25

• Manufacturer Part Number: MB3825A
• Description: 6-ch DC/DC Converter ic With Synchronous Rectifier
• Manufacturer: Fujitsu Microelectronics, Inc.

METHOD OF SETTING SOFT-START TIME
• Channels 1, 2, 4
To provide a soft-start by preventing current surges at power-on, soft-start capacitor (Cs) can be connected to
the CS terminal (pin 26) .
When the IC is started (when the CTL1 terminal (pin 30) goes to “H” level, and V
voltage) , transistors Q2 switches off and the CS terminal begins charging the external soft-start capacitors (Cs)
at 1.0 A.
The error amplifier makes a soft-start in a proportion to the output voltage to the CS teminal voltage regardless
of the load current on the DC/DC converter.
Note that the soft-start time can be calculated by the following formula.
Soft-start time (output rise time)
t
Figure 8. Soft-start circuit
S
(s)
R1
R2
R3
CSCP
A
C
C
CS
S
SCP
1.5
IN (E)1
26
23
Q2
FB1
C
S
38
39
( F) .
1 A
Q1
1 A
Buff
Soft Start
Comp.
1.5 V
Error
Amp1
1.5 V
SCP
UVLO
bias
Ref
ON/OFF
Power
Output
Output
Output
Output
stage
stage
stage
stage
CC
External PNP transistor
UVLO threshold
MB3825A
46
43
56
29
28
30
27
4
OUT1-6
OUT1-1
OUT2-1
OUT1-3
VCC
CTL1
VREF
CTL2
25