8. FUNCTIONAL DESCRIPTION
14
EPSON
S1F76980 Technical Manual (Rev.1.0)
(6) Overvoltage limiter control
If measures against overvoltage are required after output stage of V
OUT
, feed back and input voltage divided by
resistance to the FB pin. To set the V
OUT
voltage, refer to the formula below. Set so that the total resistance of
RFB1 + RFB2 is between 1 and 10 Meg
Ω
.
V
OUT
=V
REF
x
((RFB1+RFB2)/RFB2)
Incoming current can be prevented by connecting a capacitor for setting the soft start time to the CSFT pin as
measures against incoming current at cold start (no charge in the V
OUT
smoothing capacitor). The setting time
can be obtained from the following formula.
Typ.
Soft start setting time TSFT [ms] = Set coefficient (70) × C [
µ
F]
For recommended C = 0.01 [
µ
F], soft start time: TSFT = 0.7 [ms]
Fig.8.4.4 Overvoltage limiter circuit diagram
CSFT
CSFT
AMP
+
-
OC2
OC1
V
CC
OU2
OU1
V
BUS
OB2
OB1
V
BAT
V
OUT
V
OUT
V
REF
= 1.05V
RFB1
RFB2
FB
SFT
