NCP1239
regulation
Vcc
PWM
Short−circuit
Short−circuit
Stby stby is left
16.4V
Nom
Pout
11.2V
6.9V
Timer
100ms*
100ms*
100ms*
100ms*
One Vcc cycle is skipped to
lower the burst mode duty
cycle to typically 5% in
fault conditions.
0.9V
flag
7.5ms*
SS
PFC
Vcc
If the fault had disappeared
the SMPS would recover
normal operation
Standby
is confirmed
*This time is programmed by the Pin 6 capacitor. C
= 390 nF nearly sets the following intervals:
pin6
− Soft−Start Time (T ):7.5 ms
ss
jittering
− Jittering Period (T
): 10 ms
− Fault Detection Delay (T
): 100 ms
delay
More generally, the times approximately depend on C
as follows:
pin6
− T = 7.5 ms * C
/ 390 nF
ss
pin6
− T
− T
=10 ms * C
=100 ms * C
/ 390 nF
jittering
pin6
pin6
/ 390 nF
delay
Figure 38.
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