MB39A106 Datasheet, PDF (20/46 Pages) Fujitsu Component Limited. – 2-Channel DC/DC Converter IC with Overcurrent Protection Symmetrical-Phase Type

MB39A106
2. 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 the DC/DC converter load conditions are stable on both channels, the short-circuit detection comparator
keeps its output at the “H” level and the CSCP terminal (pin 11) remains at the “L” level.
If a load condition changes rapidly due to a short-circuit of the load, causing the output voltage to drop, the short-
circuit detection comparator changes its output to the “L” level. This causes the external short-circuit protection
capacitor Cscp connected to the CSCP terminal to be charged at 10 µA.
Short-circuit detection time (tSCP)
tSCP (s) =: 0.070 × CSCP (µF)
When capacitor Cscp is charged to the threshold voltage (VTH=: 0.70 V), the protection circuit sets the latch and
turns off the external FET (setting the dead time to 100%). At this time, the latch input is closed. As the result,
the CSCP terminal is held at the “L” level and the PWRGOOD terminal is set to “L” level. The protection circuit
closes both channels even when a short-circuit is detected on only either.
To reset the actuated protection circuit, either the power supply turn off and on again or set the CTL terminal
(pin 6) to the “L” level to lower the VREF terminal (pin 8) voltage to 1.7 V (Min) or less. It can also be reset by
setting both of the CTL1 terminal (pin 9) and CTL2 terminal (pin 10) to the “L” level.
(FB2)
VO
14
FB1
2
R1
(−INE2) 15
1
−INE1
R2
Error
− Amp
+
1.23 V
SCP
Comp.
10 µA
CSCP
11
CTL
CTL1
CTL2
SR
Latch
Latch2
3.1 V
VREF
UVLO
PWRGOOD
12
<Timer-latch short-circuit protection circuit>
20