AP2191D datasheet(11/18 Pages) DIODES

11 / 18 page

AP2181D/AP2191D

1.5A SINGLE CHANNEL CURRENT-LIMITED POWER

SWITCH WITH OUTPUT DISCHARGE

AP2181D/2191D

Document number: DS32251 Rev. 1 - 2

11 of 18

www.diodes.com

June 2010

Application Note (Continued)

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)× I

Finally, calculate the junction temperature:

TJ = PD x RθJA + 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 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 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 times and fall times of the AP2181D/AP2191D, 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

AP2181D/AP2191D 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 AP2181D/AP2191D 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 system surge current and provides a hot-

plugging mechanism for any device.

AP2191D датащи(PDF) 11 Page - Diodes Incorporated