Diodes AP2161D/AP2171D Manuel d'utilisateur télécharger pdf (Page 11)

AP2161D/AP2171D

Document number: DS32250 Rev. 5 - 2

11 of 19

www.diodes.com

March 2013

AP2161D/AP2171D

Application Note (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 100. 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 AP2161D/AP2171D are 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-F to 0.1-F 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-F 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-F to 0.1-F 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.

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 (T

) and R

DS(ON)

, the power dissipation can be calculated by:

= R

DS(ON)

× I

The junction temperature can be calculated by:

= P

x R



+ T

Where:

= Ambient Temperature °C

JA

= Thermal Resistance

= 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 AP2161D/AP2171D, 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 AP2161D/AP2171D 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 AP2161D/AP2171D between the V

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.

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