4A Ultra Low Dropout Positive Adjustable or Fixed-mode Regulator

AP1184

Anachip Corp.

www.anachip.com.tw

Rev.1.1 Sep 7, 2004

6/11

Functional Descriptions(Continued)

Thermal Design

The AP1184-XXX incorporates an internal thermal

shutdown that protects the device when the junction

temperature exceeds the allowable maximum

junction temperature. Although this device can

operate with junction temperatures in the range of

150

sink be chosen such that during maximum

continuous load operation, the junction temperature

is kept below this number. The example below

shows the steps in selecting the proper surface

mount package.

Assuming, the following conditions:

Vout=2.5V

Vin=3.3V

Vctrl=5V

Iout=2A DC Avg.

Calculate the maximum power dissipation using

the following equation:

Pd=Iout*(Vin-Vout)+(Iout/60)*(Vctrl-Vout)

Pd=2*(3.3-2.5)+(2/60)*(5-2.5)=1.68W

Using table below select the proper package

and the amount of copper board needed.

Package

Copper Area

Max Pd (Ta=25

Max Pd (Ta=45

SOP7

1.0” X 1.0”

65

1.7W

1.4W

TO263

Pad Size-1.4”X1.4”

25-45

2.4W-4.4W

2.0W-3.6W

Note: Above table is based on the maximum junction temperature of 135

As shown in the above table, any of the two packages will do the job. For low cost applications the SOP7 package is

recommended.