MB3825A Fujitsu Microelectronics, Inc., MB3825A Datasheet - Page 23

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

METHOD OF SETTING TIME CONSTANT FOR TIMER-LATCH SHORT PROTECTION
CIRCUIT
The short detection comparator (SCP comparator) in each of the channels constantly compares the error
amplifier output level to the reference voltage and the SCP terminal (pin 13) .
While the switching regulator load conditions are stable on all channels, or when the voltage level at the SCP
terminal is higher than the reference voltage, the short detection comparator output remains at “L” level,
transistor Q3 is turned on, and the CSCP terminal (pin 23) is held at input standby voltage (V
If the load conditions change rapidly due to a short-circuiting of load, causing the output voltage to drop, or if
the voltage at the SCP terminal falls below the reference voltage level, the output from the short detection
comparator on the corresponding channel or the input at the SCP terminal goes to “H” level. This causes transistor
Q3 to turn off and the external short protection capacitor C
Short Detection Time (t
t
When the capacitor C
PNP is turned off (inactive interval is set to 100 ) . At this point the SR latch input is closed and the C
is held at input latch voltage (V
Figure 6. Protection timer-latch short protection circuit
PE
(s) 0.7
R1
R2
R3
CSCP
A
C
CS
SCP
IN (C) 1
SCP
40
13
26
23
C
SCP
Q2
1 A
Q1
1 A
( F)
1.5 V
1.5 V
Buff
SCP
PE
Soft Start
Comp.
)
is charged to the threshold voltage V
Q3
I
protection circuit
S
short circuit
Timer-latch
50 mV) .
SCP
Comp.1
SCP
Comp.
1.5 V
bias
R
UVLO
SCP
connected to the CSCP terminal to charge at 1.0 A.
TH
bias
Ref
0.7 V the SR latch is set, and the external
ON/OFF
Power
External PNP transistor
Output
Output
Output
Output
stage
stage
stage
stage
MB3825A
STB
46
43
56
29
28
30
27
4
OUT1-6
CTL2
OUT1-1
OUT2-1
OUT1-3
VCC
CTL1
VREF
50 mV) .
SCP
terminal
23