L2800_13 Datasheet, PDF (5/7 Pages) Unisonic Technologies – SWITCHING REGULATOR CONTROLLER(LOW VOLTAGE)

L2800
 DIAGRAM
LINEAR INTEGRATED CIRCUIT
 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⁺ and capacitor C_PE starts charging i the switching regulator
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
t_PE[S]≒0.8×C_PE[μF]
2. SOFT START
Once power on, the capacitor C_PE which is connected to the SCP pin starts charging.The soft start setting
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_PE[μF]
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R103-030.C