APL3521 datasheet(11/18 Pages) ANPEC

11 / 18 page

Rev. A.1 - Aug., 2012

APL3521

www.anpec.com.tw

Function Description

VIN Under-Voltage Lockout (UVLO)

The APL3521A/B power switch is built-in an under-volt-

age lockout circuit to keep the output shut off until internal

circuitry is operating properly. The UVLO circuit has hys-

teresis and a de-glitch feature so that it will typically ig-

nore undershoot transients on the input. When input volt-

age exceeds the UVLO threshold, the output voltage starts

a soft-start to reduce the inrush current.

Power Switch

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

DS(ON). The internal power MOSFET does not have the

body diode. When IC is off, the MOSFET prevents a cur-

rent flowing from the VOUT back to VIN and VIN to VOUT.

Current-Limit Protection

The APL3521A/B power switch provides the current-limit

protection function. During current-limit, the devices limit

output current at current-limit threshold. For reliable

operation, the device should not be operated in current-

limit for extended period.

Short-Circuit Protection

When the output voltage drops below V

IN-1.5V, which is

caused by the over load or short-circuit, the devices limit

the output current down to a safe level. The short circuit

current-limit is used to reduce the power dissipation dur-

ing short-circuit condition. If the junction temperature is

over the thermal shutdown temperature, the device will

enter the thermal shutdown.

Soft-Start

The APL3521 has a built-in soft start to control the rise

rate of the during start-up. The softstart time is 2ms when

IN=5V.

Enable/Disable

Pull the ENB above 2V, or EN below 0.8V to disable the

device and pull ENB pin below 0.8V or EN above 2V to

enable the device. When the IC is disabled, the supply

current is reduced to less than 1

µA. The enable input is

compatible with both TTL and CMOS logic levels. The

EN/ENB pins cannot be left floating.

Over-Temperature Protection

When the junction temperature exceeds 140oC, 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 20oC, 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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