L2800

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

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www.unisonic.com.tw

QW-R103-030,B

DIAGRAM

HOW TO SET THE TIME CONSTANT FOR SHORT CIRCUIT DETECTION AND SOFT

START

1. SHORT CIRCUIT PROTECTION

Te error amplifier output (FB pin) is fixed at VOM

output suddenly drops due to load effect. The output pin is set low and the SCP pin stays low when the voltage at

the SCP pin reaches approximately 0.8V.

As the protection circuit operates, by resetting the power supply the circuit will be restored.

•Short circuit detection time

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2. SOFT START

voltage is compared by the PWM comparator as the voltage’s proportion at the SCP pin with the sawtooth

waveform. The comparison controls the OUT pin’s ON duty,which is causing the soft start operation. During the

time for completion of soft start operation, the SCP pin’s voltage stays low, but the soft start setting voltage stays

high, and the circuit then enters the output short circuit detection wait state.

Soft start time (until the output ON duty reaches approximately 50%)

ts[S] 0.35*C

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