AAT1110 Datasheet, PDF (5/17 Pages) Advanced Analog Technology, Inc. – ONE-CHANNEL STEP-DOWN PWM CONTROLLER

Advanced Analog Technology, Inc.
AAT1110
How to Set the Time Constant for Soft-Start and Short Circuit Protection
1. Soft-Start
At power on, the AAT1110 operates in soft-start mode. The capacitor C_SCP connected to SCP pin starts
charging at a constant current. In the soft-start mode, the voltage at SCP pin ( V_SCP ) is input to the PWM
comparator, so that the ON duty of the OUT pin is controlled by the V_SCP . At completion of the soft-start
operation, the voltage at the SCP pin stays low; the input from soft-start circuit to the PWM comparator
stays high, and enters the short circuit protection waiting state.
Soft-Start Time
t_s (sec) ~ 0.84 × C_SCP (µF)
2. Short Circuit Protection
If the switching regulator output suddenly drops due to loading effect, the error amplifier output will be
fixed at V_OM+ and capacitor C_SCP will start charging. When the voltage at the SCP pin reaches
approximately 1.26V, the output pin will set low and SCP pin will remain low.
Once the protection circuit starts operating, the circuit can be recovered by setting the power supply.
Short Circuit Detection Time
t _scp (sec) ~ 0.84 × C_SCP (µF)
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– Advanced Analog Technology, Inc. –
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