F72820

Jul 2007

V0.24P

-6-

F72820

VOUT

Q1

Q2

UGATE

LGATE

PHASE

BOOT

VIN = 5V

OCSET

40uA

OC

OVER-CURRENT TRIP:

>

Figure 6

6.5 Under-voltage Protection

Pins FB are monitored during converter operation by under-voltage (UV) comparators. If the FB voltage drops below

0.5V, a fault signal is generated. The internal fault logic shut down regulator simultaneously when the fault signal

triggers a restart. At time t0, VOUT has dropped below 0.5V of the nominal output voltage. Output is quickly shut

down and the internal soft-start function begins producing soft-start ramps. The delay interval, t0 to 3*tss, seen by

the output is equivalent to three soft-start cycles. After a short delay interval of 10.5ms, the fourth internal soft-start

cycle initiates a normal soft-start ramp of the output, at time 3*tss. Both outputs are brought back into regulation by

time 4*tss, as long as the UV event has cleared. When the cause of the UV still been present after the delay interval.

A fault signal could then be generated and the outputs once again shutdown.

t0

tss

2tss

3tss

4tss

TIME

0V

1.5V

3V

Delay interval

VOUT

Figure 7