MB3881 Datasheet, PDF (26/40 Pages) Fujitsu Component Limited. – 8-ch DC/DC Converter IC with Synchronous Rectifier for Voltage Step-up and Step-down

MB3881
s SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT
The short detection comparator (SCP comparator) in each channel monitors the output voltage.
While the switching regulator load conditions are stable on all channels, the LOG_SCP output remains at "H"
level, transistor Q1 is turned on, and the CSCP terminal (pin 26) is held at “L” level.
If the load condition on a channel changes rapidly due to a short of the load, causing the output voltage to drop,
the output of the short detection comparator on that channel goes to “H” level. This causes transistor Q1 to be
turned off and the external short protection capacitor CSCP connected to the CSCP terminal to be charged at 1.0
µA.
When the capacitor CSCP is charged to the threshold voltage (VTH =: 0.70 V), the latch is set and the external
FET is turned off (dead time is set to 100%). At this point, the latch input is closed and the CSCP terminal is
held at “L” level.
Short detection time (tPE)
tPE (s) =: 0.70 × CSCP (µF)
VO1
R1
46
−IN1
R2
1.0 V
SCP
− ^Comp.1
+
+
External PNP transistor
Drive
1−1
50
OUT1−1
Drive
1−2
51
OUT1−2
−IN8(C)
7
+IN8(C)
8
CSCP
26
1 µA
CSCP
Q1
SCP
− Comp.8
+
LOG_SCP
Drive
8
bias
bias
S
R
Timer-latch short
protection circuit
UVLO
Ref
Power
ON/OFF CTL
Timer-latch short circuit protection circuit
64
OUT8
28
CTL−1
26