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AP2111

2A SINGLE CHANNEL CURRENT-LIMITED POWER SWITCH

Diodes Incorporated. 

AP2101/AP2111

2A SINGLE CHANNEL CURRENT-LIMITED POWER

SWITCH

Application Note

Power Supply Considerations

A 0.1-μF to 1-μF X7R or X5R ceramic bypass capacitor between IN and GND, close to the device, is

recommended. 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 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.

Over-current and Short Circuit Protection

An internal sensing FET is employed to check for over-current conditions. Unlike current-sense resistors,

sense FETs do not increase the series resistance of the current path. When an overcurrent condition is

detected, the device maintains a constant output current and reduces the output voltage accordingly.

Complete shutdown occurs only if the fault stays long enough to activate thermal limiting.

Three possible overload conditions can occur. In the first condition, the output has been shorted to

GND before the device is enabled or before VIN has been applied. The AP2101/AP2111 senses the short

circuit and immediately clamps output current to a certain safe level namely ILIMIT.

In the second condition, an output short or an overload occurs while the device is enabled. At the instance

the overload occurs, higher current may flow for a very short period of time before the current limit function

can react. After the current limit function has tripped (reached the over-current trip threshold), the device

switches into current limiting mode and the current is clamped at ILIMIT.

In the third condition, the load has been gradually increased beyond the recommended operating current.

The current is permitted to rise until the current-limit threshold (ITRIG) is reached or until the thermal limit of

the device is exceeded. The AP2101/AP2111 is capable of delivering current up to the current-limit threshold

without damaging the device. Once the threshold has been reached, the device switches into its current

limiting mode and is set at ILIMIT.

To protect against short circuit to GND at extremely low temperature (< -30oC), a minimum 120-μF

electrolytic capacitor on the output pin is recommended. A correct capacitor type with capacitor voltage

rating and temperature characteristics must be properly chosen so that capacitance value does not drop too

low at the extremely low temperature operation. A recommended capacitor should have temperature

characteristics of less than 10% variation of capacitance change when operated at extremely low temp.

Our recommended aluminum electrolytic capacitor type is Panasonic FC series.

At low input voltage condition (VIN < 3V), the short circuit protection current may rise as high as twice the

typical value.

FLG Response

When an over-current or over-temperature shutdown condition is encountered, the FLG open-drain output

goes active low after a nominal 7-ms deglitch timeout. 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. The AP2101/AP2111 is designed to eliminate false over-current reporting without the need

of external components to remove unwanted pulses.

Power Dissipation and Junction Temperature

The low on-resistance of the internal MOSFET allows the small surface-mount packages to pass large

current. Using the maximum operating ambient temperature (TA) and RDS(ON), the power dissipation can be

calculated by:

PD = RDS(ON)× I2

AP2101/AP2111 Rev. 2

10 of 14

www.diodes.com

MARCH 2010

© Diodes Incorporated

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