MB39A123 Datasheet, PDF (25/44 Pages) Fujitsu Component Limited. – 6 ch DC/DC Converter IC with Synchronous Rectification

MB39A123
■ SETTING THE TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION
CIRCUIT
Each channel uses the short-circuit detection comparator (SCP) to always compare the error amplifier’s output
level to the reference voltage.
While DC/DC converter load conditions are stable on all channels, the short-circuit detection comparator output
remains at “L” level, and the CSCP terminal (pin 13) is held at “L” level.
If the load condition on a channel changes rapidly due to a short-circuit of the load, causing the output voltage
to drop, the output of the short-circuit detection comparator on that channel goes to “H” level.
This causes the external short-circuit protection capacitor CSCP connected to the CSCP terminal (pin 13) to be
charged at 1 µA.
Short-circuit detection time : tCSCP
tCSCP (s) =: 0.70 × CSCP (µF)
When the capacitor CSCP is charged to the threshold voltage (VTH =: 0.70 V) , the latch is set to and the external
FET is turned off (dead time is set to 100%) . At this time, the latch input is closed and CSCP terminal (pin 13)
is held at “L” level.
The short-circuit detection from external input is capable by using −INS terminal (pin 8) . In this case, the short-
circuit detection operates when the −INS terminal voltage becomes the level of the threshold voltage (VTH =: IV)
or less.
Note that the latch is reset as the voltage at the VREF terminal (pin 9) is decreased to 1.27 V (Min) or less by
either recycling the power supply or setting the CTL terminal (pin 1) to “L” level.
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