MB3885 Datasheet, PDF (14/29 Pages) Fujitsu Component Limited. – 1-channel DC/DC Converter IC with Synchronous Rectifier

MB3885
2. Control Functions
Output ON/OFF control is provided by using the CS terminal (pin 6) setting functions.
Output On/Off Setting Functions
CS terminal voltage level
Output state
GND
OFF
Hi-Z
ON
3. Protective Functions
(1) Timer Latch Short Circuit Protection (SCP)
The short circuit protection comparators read the output voltage levels. If the output voltage falls below the short
detection voltage, the timer circuit is activated to start charging the external capacitor Cscp connected to the
CSCP terminal (pin 3) .
When capacitor voltage reaches approximately 0.68 V the output FET turns off, setting the idle interval to 100%.
Once the protection circuit is activated, it can be reset by turning the power supply off and on again. (See “Setting
the Timer Latch Short Circuit Protector Time Constant.”)
(2) Undervoltage Lockout Circuit Block (UVLO)
Transient status during normal power-on or momentary drops in supply voltage can cause abnormal operation
in an control IC, leading to damage or degradation of system components. The undervoltage lockout circuit
prevents such abnormal operations by reading the internal reference voltage level and switching the output FET
off, setting the idle interval to 100% and holding the CSCP terminal (pin 3) to “L” level.
System operation is restored when the supply voltage rises back about the undervoltage lockout circuit threshold
voltage.
(3) Overvoltage Protection Block (OVP)
The overvoltage protection circuit uses an overvoltage comparator (OVP Comp.) to read the output voltage
levels from the DC/DC converter. If the output voltage exceeds the threshold voltage a latch is set, turning off
the main side FET.
Once the protector circuit is activated, it can be reset by switching the power supply off and on again.
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