NCP1236
www.onsemi.com
24
Overcurrent protection with Fault timer
When an overcurrent occurs on the output of the power
supply, the FB loop asks for more power than the controller
can deliver, and the CS setpoint reaches V
ILIMIT
. When this
event occurs, an internal t
fault
timer is started: once the timer
elapsed, DRV pulses are stopped and the controller is either
latched off (latched protection, version A), or it enters an
autorecovery mode (version B). The timer is reset when the
CS setpoint goes back below V
ILIM
before the timer elapses.
The fault timer is also started if the driver signal is reset by
the max duty cycle.
CS
FB
−
+
tLEB
blanking
/ 5
−
+
+
VILIM
Protection
Mode
Brown−out
tfault
timer
release
t autorec
timer
Reset
Autorecovery
protection
mode only
R
S
Q
PWM
Reset DRV
Fault Flag
DC MAX
DRV
Figure 44. Timer−Based Overcurrent Protection
In autorecovery mode, the controller tries to restart after
t
autorec
. If the fault has gone, the supply resumes operation;
if not, the system starts a new burst cycle.
