MB3883 Datasheet, PDF (19/39 Pages) Fujitsu Component Limited. – 6-ch DC/DC Converter IC With Synchronous Rectification for voltage step-up and step-down

MB3883
2. Channel Control Function
Channels are turned on and off depending on the voltage levels at the CTL terminal (pin 20), CTL1, 2 terminal
(pin 21), CTL3 terminal (pin 22), CTL4 terminal (pin 23), and CTL5 terminal (pin 24).
Channel On/Off Setting Conditions
Voltage level at CTL pin
Channel on/off state
CTL CTL1, 2 CTL3 CTL4 CTL5 Power/CH6 CH1, CH2 CH3
CH4
CH5
L
×
×
×
×
OFF (Standby state)
L
L
L
H
H
L
L
H
L
L
H
H
H
L
H
H
ON
L
L
L
H
H
L
H
H
L
L
H
H
H
L
H
OFF
ON
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
OFF
ON
ON
ON
OFF
ON
OFF
OFF
OFF
ON
ON
OFF
ON
OFF
OFF
ON
ON
ON
OFF
ON
× : Undefined
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 18).
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 18) 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.
(3) Output switch control circuit
When the power is turned on, this circuit prevents reactive current flow to external step-up circuits on CH5 and
CH6. When the SWIN terminal (pin 2) is a state at “H” level after releasing UVLO and the C+IN6 terminal (pin5)
voltage goes above 0.9 V (Typ.), the SWOUT terminal (pin 1) becomes “L” level. External P-ch MOS FET is
turned on at this time and the output voltage is generated.
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