NCP1237 datasheet(20/34 Pages) ONSEMI

20 / 34 page

NCP1237

http://onsemi.com

OVERCURRENT PROTECTION WITH FAULT TIMER

Classical Overcurrent Protection

When an overcurrent occurs on the output of the power

supply, the feedback loop asks for more power than the

controller can deliver, and the CS setpoint reaches VILIM.

When this event occurs, an internal tfault timer is started:

once the timer times out, 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

VILIM before the timer elapses. The fault timer is also started

if the driver signal is reset by the max duty ratio.

Figure 17. Timer−Based Overcurrent Protection

−

tLEB

blanking

/ 5

−

VILIM

Protection

Mode

Brown−out

tfault

timer

release

t autorec

timer

Reset

Autorecovery

protection

mode only

PWM

Reset DRV

Fault Flag

DC MAX

DRV

In autorecovery mode, the controller tries to restart after

tautorec. If the fault has gone, the supply resumes operation;

if not, the system starts a new burst cycle (see Figure 18).

NCP1237 Datasheet(PDF) 20 Page - ON Semiconductor