AP2141D Просмотр технического описания (PDF) - Diodes Incorporated.

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AP2141D

0.5 SINGLE CHANNEL CURRENT-LIMITED POWER SWITCH WITH OUTPUT DISCHARGE

Diodes Incorporated. 

AP2141D/ AP2151D

Application Information (cont.)

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 100Ω. 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. The 7-ms timeout is also applicable for Over-current recovery and Thermal recovery. The

AP2141D/AP2151D are designed to eliminate erroneous Over-current reporting without the need for external components, such as an RC delay

network.

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 the output

from going negative during turn-off due to inductive parasitics.

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

The junction temperature can be calculated by:

TJ = PD x RJA + TA

Where:

TA= Ambient temperature °C

RθJA = Thermal resistance

PD = Total power dissipation

Generic Hot-Plug Applications

In many applications it may be necessary to remove modules or PC boards while the main unit is still operating. These are considered hot-plug

applications. Such implementations require the control of current surges as seen by the main power supply and the card being inserted. The most

effective way to control these surges is to limit and slowly ramp up the current and voltage being applied to the card, similar to the way in which a

power supply normally turns on. Due to the controlled rise and fall times of the AP2141D/AP2151D, these devices can be used to provide a softer

start-up to devices being hot-plugged into a powered system. The UVLO feature of the AP2141D/AP2151D also ensures that the switch is off after

the card has been removed, and that the switch is off during the next insertion.

By placing the AP2141D/AP2151D between the VCC input and the rest of the circuitry, the input power reaches these devices first after insertion.

The typical rise time of the switch is approximately 1ms, providing a slow voltage ramp at the output of the device. This implementation controls the

system surge current and provides a hot-plugging mechanism for any device.

AP2141D/ AP2151D

Document number: DS32242 Rev. 4 - 2

11 of 18

www.diodes.com

May 2013

© Diodes Incorporated

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