Datasheet

UDG−95106
1.2 V
5 V
1.2 V
0.2 V
ON
OFF
FAULT
V
SS
PWM
UC2825A-EP
www.ti.com SGLS305D –JULY 2005–REVISED SEPTEMBER 2010
Undervoltage Lockout (UVLO), Soft-Start, and Fault Management
Soft-start is programmed by a capacitor on the soft-start (SS) pin. At power up, SS is discharged. When SS is
low, the error-amplifier output also is forced low. While the internal 9-mA source charges SS, the error-amplifier
output follows until closed-loop regulation takes over.
Anytime ILIM exceeds 1.2 V, the fault latch is set and the output pins are driven low. The soft-start cap then is
discharged by a 250-mA current sink. No more output pulses are allowed until soft-start is fully discharged and
ILIM is below 1.2 V. At this point, the fault latch resets and the chip executes a soft-start.
Should the fault latch get set during soft-start, the outputs are terminated immediately, but the soft-start capacitor
does not discharge until it has been fully charged first. This results in a controlled hiccup interval for continuous
fault conditions.
Figure 5. Soft-Start and Fault Waveforms
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