MB3800PFV-E1 参数 Datasheet PDF下载

MB3800

■

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

DETECTION

1. Soft Start

At power on, the capacitor C

PE

connected to the SCP pin (pin 2) starts charging. The PWM comparator compares

the soft start setting voltage as a proportion of the voltage at the SCP pin with the sawtooth waveform.

The comparison controls the ON duty of the OUT pin (pin 5), causing the soft start operation. On completion of soft

start operation, the voltage at the SCP pin stays low, the soft start setting voltage stays high, and the circuit enters

the output short circuit detection wait state.

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

t

S

[s]

≅

0.35

×

C

PE

[µF]

2. Short Circuit Protection

If the switching regulator output suddenly drops due to load effect, the error amplifier output (FB pin (pin 8)) is fixed

at VOM

+

and capacitor C

PE

starts charging. When the voltage at the SCP pin reaches approximately 0.8 V, the OUT

pin (pin 5) is set low and the SCP pin (pin 2) stays low.

Once the protection circuit operates, the circuit can be restored by resetting the power supply.

• Short circuit detection time

t

PE

[s]

≅

0.8

×

C

PE

[µF]

7