MB3817_03 Datasheet, PDF (12/28 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3817
3. Protective Circuit Functions
(1) Soft start and short protection circuits (CS, SCP)
Soft starting, by preventing a rush current at power-on, can be provided by connecting a capacitor CS to the CS
terminal (pin 13) .
After the soft start operation is completed, the CSCP terminal (pin 14) is held at “L” level (standby voltage VSTB),
which functions as short detection standby mode. If an output short causes the error amp. output to rise above
1.5 V, capacitor CSCP begins charging, and after reaching threshold voltage VTH of 0.65 V causes the OUT terminal
(pin 10) to be fixed at “H” level and the dwell time to be set to 100%, and the CSCP terminal (pin 14) is held at
“L” level.
Once the protection circuit has been activated, the power supply must be reset to restore operation.
(2) Low input voltage error prevention circuit (UVLO)
Power-on surges and momentary drops in power supply voltage can cause errors in control IC operation, which
can destroy or damage systems. The low input voltage error protection circuit compares the supply voltage to
the internal reference voltage, and sets the OUT terminal (pin 10) to “H” level in the event of a drop in supply
voltage.
Operation is restored when the power supply voltage returns above the threshold voltage of the low input voltage
error prevention circuit.
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