APL3533 datasheet(14/21 Pages) ANPEC

14 / 21 page

Rev. A.2 - Mar., 2013

APL3533

www.anpec.com.tw

Function Description

VIN Under-voltage Lockout (UVLO)

A under-voltage lockout (UVLO) circuit monitors the VBIAS

pins voltage to prevent wrong logic controls. The UVLO

function initiates a soft-start process after the BIAS sup-

ply voltages exceed rising UVLO voltage threshold dur-

ing powering on.

Power Switch

The power switch is an N-channel MOSFET with a ultra-

low R

DS(ON). When IC is in shutdown state (VEN1,2=0V), the

MOSFET prevents a reverse current flowing from the VOUT

back to VIN. When IC is in UVLO state, the internal para-

sitic diodes connected from VOUT to VIN will be forward

biased.

Soft-start

The APL3533 Provides an adjustable soft-start circuitry

to control rise rate of the output voltage and limit the cur-

rent surge during start-up. The soft-start time is set with a

capacitor from the SS pin to the ground.

Enable Control

The APL3533 has a dedicated enable pin (EN). A logic

low signal applied to this pin shuts down the output. Fol-

lowing a shutdown, a logic high signal re-enables the

output through initiation of a new soft-start cycle.

Over-Temperature Protection (OTP)

When the junction temperature exceeds 160oC, the inter-

nal thermal sense circuit turns off the power FET and

allows the device to cool down. When the device’s junc-

tion temperature cools by 40oC, the internal thermal

sense circuit will enable the device, resulting in a pulsed

output during continuous thermal protection. Thermal

protection is designed to protect the IC in the event of

over temperature conditions. For normal operation, the

junction temperature cannot exceed T

J=+125

oC.

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