AP2141D/AP2151D

0.5A SINGLE CHANNEL CURRENT-LIMITED POWER

SWITCH WITH OUTPUT DISCHARGE

AP2141D/2151D

Document number: DS32242 Rev. 1 - 2

11 of 18

www.diodes.com

June 2010

© Diodes Incorporated

Thermal Protection

Thermal protection prevents the IC from damage when the die temperature exceeds safe margins. This mainly

occurs when heavy-overload or short-circuit faults are present for extended periods of time. The

AP2141D/AP2151D implements a thermal sensing to monitor the operating junction temperature of the power

distribution switch. Once the die temperature rises to approximately 140°C, the Thermal protection feature gets

activated as follows: The internal thermal sense circuitry turns the power switch off and the FLG output is asserted

thus preventing the power switch from damage. Hysteresis in the thermal sense circuit allows the device to cool

down to approximately 25°C before the output is turned back on. This built-in thermal hysteresis feature is an

excellent feature, as it avoids undesirable oscillations of the thermal protection circuit. The switch continues to

cycle in this manner until the load fault is removed, resulting in a pulsed output. The FLG open-drain output is

asserted when an over-current occurs with 7-ms deglitch.

Reverse Current Protection

In a normal MOSFET switch, current can flow in reverse direction (from the output side to the input side) when the

output side voltage is higher than the input side, even when the switch is turned off. A reverse-current blocking

feature is implemented in the AP21x1 series to prevent such back currents. This circuit is activated by the

difference between the output voltage and the input voltage. When the switch is disabled, this feature blocks

reverse current flow from the output back to the input.

Special Functions:

Discharge Function

When enable is de-asserted, the discharge function is active. The output capacitor is discharged through an

internal NMOS that has a discharge resistance of 100

Ω. Hence, the output voltage drops down to zero. The time

taken for discharge is dependent on the RC time constant of the resistance and the output capacitor.

FLG Response

The FLG open-drain output goes active low for any of the two conditions: Over-Current or Over-Temperature. The

time from when a fault condition is encountered to when the FLG output goes low is 7-ms (TYP). The FLG output

remains low until both over-current and over-temperature conditions are removed. Connecting a heavy capacitive

load to the output of the device can cause a momentary Over-current condition, which does not trigger the FLG

due to the 7-ms deglitch timeout. This 7-ms timeout is also applicable for Over-current recovery and Thermal

recovery. The AP2141D/AP2151D is designed to eliminate erroneous Over-current reporting without the need for

external components, such as an RC delay network.

Applications Information:

Power Supply Considerations

A 0.01-

μF to 0.1-μF X7R or X5R ceramic bypass capacitor between IN and GND, close to the device, is

recommended. This limits the input voltage drop during line transients. Placing a high-value electrolytic capacitor

on the input (10-

μF minimum) and output pin(s) is recommended when the output load is heavy. This precaution

also reduces power-supply transients that may cause ringing on the input. Additionally, bypassing the output with

a 0.01-

μF to 0.1-μF ceramic capacitor improves the immunity of the device to short-circuit transients. This

capacitor also prevents output from going negative during turn-off due to inductive parasitics.