MB39A112 Datasheet, PDF (16/35 Pages) Fujitsu Component Limited. – 3-ch DC/DC Converter IC

MB39A112
s SETTING TIME CONSTANT FOR TIMER-LATCH SHORT-CIRCUIT PROTECTION CIRCUIT
Each channel uses the short-circuit detection comparator (SCP Comp.) 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 14) 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 goes to “H” level. This causes the extemal short-
circuit protection capacitor CSCP connected to the CSCP terminal to be charged at 1 µA.
Short-circuit detection time : tcscp
tcscp[s] =: 0.72 × CSCP [µF]
When the capacitor CSCP is charged to the threshold voltage (VTH=: 0.72 V) , the latch is set and the external FET
is turned off (dead time is set to 100 %) . At this time, the latch input is closed and the CSCP terminal
(pin 14) is held at “L” level.
If any of CH1 to CH3 detects a short circuit, all the channels are stopped.
• Timer-latch short-circuit protection circuit
VO
−INE1
R1
(−INE2)
(−INE3)
VREF
R2
10 µA
CS1
(CS2)
(CS3)
FB1
(FB2)
(FB3)
Error
− ^Amp
++
1.23 V
/1.0 V
SCP
Comp.
[SCP]
1 µA
2.7 V
H: UVLO release
CSCP
14
SR
Latch
VCC
UVLO
H: at SCP
16