MB39A115 Datasheet, PDF (17/42 Pages) Fujitsu Component Limited. – 5 ch DC/DC Converter IC with Synchronous Rectification

MB39A115
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 15).
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 10).
When the protection circuit is actuated, the power supply is recycled or the CTL terminal (pin 6) is set to "L"
level, resetting the latch as the voltage at the VREF terminal (pin 11) 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 (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 15) at the "L" level.
The system returns to the normal state when the power supply voltage reaches the threshold voltage of the
under-voltage lockout protection circuit.
■ PROTECTION CIRCUIT OPERATING FUNCTION TABLE
The following table shows the state that the protection circuit is operating.
Operation circuit
OUT1-1 OUT1-2 OUT2
Short-circuit protection circuit
H
L
H
Under voltage lockout protection circuit
H
L
H
OUT3
H
H
OUT4
H
H
OUT5
L
L
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