MB3881 Datasheet, PDF (18/40 Pages) Fujitsu Component Limited. – 8-ch DC/DC Converter IC with Synchronous Rectifier for Voltage Step-up and Step-down

MB3881
2. Channel Control Function
Channels are turned on and off depending on the voltage levels at the CTL-1 terminal (pin 28), CTL-2 terminal
(pin 29), CTL-3 terminal (pin 30),and CTL-4 terminal (pin 31).
Channel On/Off Setting Conditions
Voltage level at CTL pin
Channel on/off state
CTL-1
CTL-2
CTL-3
CTL-4
Power
CH8
CH1, 3, 4
CH2
CH5, 6
L
×
×
×
OFF (Standby state)
L
L
H
L
L
H
H
H
L
L
H
H
L
H
H
× : Undefined
OFF
OFF
ON
ON
OFF
ON
ON
CH7
OFF
ON
OFF
ON
OFF
ON
OFF
ON
3. Protective Functions
(1) Timer-latch short-circuit protection circuit
The short-circuit detection comparator in each channel detects the output voltage level and, if any channel output
voltage falls below the short-circuit detection voltage, the timer circuits is actuated to start charging the external
capacitor CSCP connected to the CSCP terminal (pin 26).
When the capacitor voltage reaches about 0.70 V, the circuit is turned off the output transistor and sets the dead
time to 100%.
To reset the actuated protection circuit, turn the power supply on back. (See “SETTING TIME CONSTANT FOR
TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT”.)
(2) Undervoltage lockout protection circuit
The transient state or a momentary decrease in supply voltage, which occurs when the power supply is turned
on, may cause the IC to malfunction, resulting in breakdown or degradation of the system. To prevent such
malfunctions, the undervoltage lockout protection circuit detects a decrease in internal reference voltage with
respect to the power supply voltage, turns off the output transistor, and sets the dead time to 100% while holding
the CSCP terminal (pin 26) at the “L” level.
The circuit restores the output transistor to normal when the supply voltage reaches the threshold voltage of the
undervoltage lockout protection circuit.
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