NCP1239
http://onsemi.com
20
*This time is programmed by the Pin 6 capacitor. C
pin6
= 390 nF nearly sets the following intervals:
− Soft−Start Time (T
ss
):7.5 ms
− Jittering Period (T
jittering
): 10 ms
− Fault Detection Delay (T
delay
): 100 ms
More generally, the times approximately depend on C
pin6
as follows:
− T
ss
= 7.5 ms * C
pin6
/ 390 nF
− T
jittering
=10 ms * C
pin6
/ 390 nF
− T
delay
=100 ms * C
pin6
/ 390 nF
Figure 38.
Vcc
PWM
Timer
0.9V
flag
PFC
Vcc
regulation
100ms*
16.4V
11.2V
6.9V
100ms*
100ms*
100ms*
7.5ms*
SS
Short−circuit
Stby stby is left
Standby
is confirmed
Nom
Pout
Short−circuit
One Vcc cycle is skipped to
lower the burst mode duty
cycle to typically 5% in
fault conditions.
If the fault had disappeared
the SMPS would recover
normal operation
