APL3518 datasheet(13/21 Pages) ANPEC

13 / 21 page

Rev. A.3 - Apr., 2011

APL3518/9

www.anpec.com.tw

Function Description

VIN Under-Voltage Lockout (UVLO)

The APL3518/9 series of power switches have a built-in

under-voltage lockout circuit to keep the output shutting

off until internal circuitry is operating properly. The UVLO

circuit has hysteresis and a de-glitch feature so that it will

typically ignore undershoot transients on the input. When

input voltage 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 APL3518/9 series of power switches provide the cur-

rent-limit protection function. During current-limit, the de-

vices 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 1.5V, which is

caused by an over-load or a 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 conditions. If the junction temperature

reaches over-temperature threshold, the device will en-

ter the thermal shutdown.

OCB Output

The APL3158/9 series of power switches provide an

open-drain output to indicate that a fault has occurred.

When any of current-limit or over-temperature protection

occurs for a deglitch time of t

D(OCB), the OCB goes low.

Since the OCB pin is an open-drain output, connecting a

resistor to a pull high voltage is necessary.

Enable/Disable

Pull the ENB above 2V or EN below 0.8V will disable the

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

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

current is reduced to less than 1

µA. The enable input is

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.

compatible with both TTL and CMOS logic levels. The

EN/ENB pin cannot be left floating.

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