FA13842 Datasheet, PDF (12/15 Pages) Fuji Electric – CMOS IC(For Switching Power Supply Control)

FA13842, 13843, 13844, 13845
4. Soft start
A soft-start circuit is shown in Fig. 15.
An aproximate soft-start time is determined with the following
calculation. This soft-start time is defined as the time the ISNS
terminal threshold voltage increases from 0V to 1V.
tsoft-start [ms]=4.3•C9[µF]
5. Suppression of noise at the current sensing
terminal
As each cycle current value is monitored in the current mode
control, there is the possibility that a malfunction will occur
even with a relatively low noise level. Therefore, it is
necessary to add a CR filter to reduce the level of noise at the
current sensing terminal. (See Fig. 16.)
6. ON/OFF circuit with an external signal
A typical ON/OFF circuit is shown in Fig. 17.
The output stage (OUT terminal) is enabled when the voltage
at the FB terminal is reduced to less than 2.0V and is disabled
when the FB terminal voltage increases to more than 3V.
Set the voltage of the FB terminal at a maximum of 5.3V in this
case.
8
REF
4
R17
2
D7 _1MΩ
D8
1
C9
OSC
1mA
+
2R
ER AMP
1R
5
Fig. 15
AC INPUT
DB
~+
~
T1
+
C1
6
FA13842
3
MOSFET
R18
C10
Rs
Fig. 16
7
8
30V
REF
R19 ⁴
2
ON/OFF signal
Tr6
1
+
ER AMP
OSC
2R
1R
5
Fig. 17
12