MB39A123 Datasheet, PDF (19/44 Pages) Fujitsu Component Limited. – 6 ch DC/DC Converter IC with Synchronous Rectification

MB39A123
3. Protection Function
(1) Timer-latch short-circuit protection circuit (SCP, SCP Comp.)
The short-circuit detection comparator (SCP) detects the output voltage level of each channel. If the output
voltage of any channel is lower than the short-circuit detection voltage, the timer circuit is actuated to start
charging to the capacitor (Cscp) externally connected to the CSCP terminal (pin 13).
When the capacitor (Cscp) voltage becomes about 0.7 V, the output transistor is turned off and the dead time
is set to 100%.
The short-circuit detection from external input is capable by using −INS terminal (pin 8) on short-circuit detection
comparator (SCP Comp.) .
When the protection circuit is actuated, the power supply is rebooted or the CTL terminal (pin 1) is set to "L"
level, resetting the latch as the voltage at the VREF terminal (pin 9) becomes 1.27 V (Min) or less (Refer to
“■SETTING THE TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT”) .
(2) Under voltage lockout protection circuit block (UVLO)
The transient state or a momentary decrease in the power supply voltage, which occurs when the power supply
is turned on, may cause the control IC to malfunction, resulting in the breakdown or degradation of the system.
To prevent such malfunctions, under voltage lockout protection circuit detects a decrease in internal reference
voltage level 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 13) at the "L" level.
The system returns to the normal state when the power supply voltage reaches the reference voltage of the
under voltage lockout protection circuit.
(3) Protection circuit operating function table
The following table shows the output state that the protection circuit is operating.
Operation circuit
OUT1-1 OUT1-2 OUT2 OUT3 OUT4
Short-circuit protection circuit
H
L
H
H
H
Under voltage lockout protection circuit
H
L
H
H
H
OUT5
L
L
OUT6
L
L
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