mb3881pff Fujitsu Microelectronics, Inc., mb3881pff Datasheet - Page 18

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mb3881pff

Manufacturer Part Number
mb3881pff
Description
8-ch Dc/dc Converter Ic With Synchronous Rectifier For Voltage Step-up And Step-down
Manufacturer
Fujitsu Microelectronics, Inc.
Datasheet

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18
MB3881
2. Channel Control Function
3. Protective Functions
(1) Timer-latch short-circuit protection circuit
(2) Undervoltage lockout protection circuit
CTL-1
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).
: Undefined
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 C
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”.)
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.
H
L
Voltage level at CTL pin
SCP
CTL-2
H
L
connected to the CSCP terminal (pin 26).
CTL-3
H
H
L
L
Channel On/Off Setting Conditions
CTL-4
H
H
H
H
L
L
L
L
Power
ON
CH1, 3, 4
CH8
Channel on/off state
OFF (Standby state)
CH2
OFF
ON
CH5, 6
OFF
OFF
ON
ON
CH7
OFF
OFF
OFF
OFF
ON
ON
ON
ON

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