MB3885 Fujitsu Microelectronics, Inc., MB3885 Datasheet - Page 15

• Manufacturer Part Number: MB3885
• Description: 1-channel Dc/dc Converter Ic With Synchronous Rectifier
• Manufacturer: Fujitsu Microelectronics, Inc.

SETTING THE TIMER LATCH SHORT CIRCUIT PROTECTOR TIME CONSTANT
The error Amp. output level constantly compares operation with the short circuit protection comparator as the
reference voltage.
When the DC/DC comparator load conditions are stable, the short circuit protection comparator output is at “H”
level, transistor Q1 is on, and the CSCP terminal (pin 3) is held at input standby voltage
If load conditions change rapidly, such as during a load short, causing output voltage to drop, the short circuit
protection comparator output goes to “L” level. This causes the transistor Q1 to shut off, charging the short circuit
protection capacitor Cscp (connected to the CSCP terminal) at 1 A.
When the capacitor Cscp is charted to the threshold voltage (V
FET off (setting the idle interval to 100 ) . At this time the latch input is closed and the CSCP terminal is held
at the input latch voltage (V
(V
Short detection time
tscp (s) : = 0.68
STB
CSCP
C
C
:
S
SCP
INE
CS
FB
50 mV) .
7
8
6
3
Q1
1 A
Cscp ( F)
Q4
Q2
I
10 A
:
Timer Latch Short Circuit Protection Circuit
1.25 V
SCP Comp.
50 mV) .
S
Latch
bias
Error
Amp.
R
2.1 V
UVLO
TH
:
0.68 V) a latch is set, turning the external
Drive
Drive
MB3885
13
15
OUT1
OUT2
15