 2003 Microchip Technology Inc.

DS21662C-page 11

TC2014/2015/2185

5.0

THERMAL CONSIDERATIONS

5.1

Power Dissipation

The amount of power the regulator dissipates is prima-

rily a function of input voltage, output voltage and

output current.

The following equation is used to calculate worst-case

power dissipation:

EQUATION

a function of the maximum ambient temperature

tion-to-air (

of approximately 220°C/Watt when mounted on a

typical two layer FR4 dielectric copper clad PC board.

EQUATION

is within limits. For example:

Actual power dissipation:

Maximum allowable power dissipation:

In this example, the TC2014 dissipates a maximum of

only 26.7 mW; far below the allowable limit of 318 mW.

tion can be used to calculate maximum current and/or

input voltage limits.

5.2

Layout Considerations

The primary path of heat conduction out of the package

is via the package leads. Therefore, layouts having a

ground plane, wide traces at the pads and wide power

supply bus lines combine to lower

increase the maximum allowable power dissipation

limit.

–

≈

Where:

= Worst-case actual power dissipation

= Maximum output (load) current

Where all terms are previously defined.

–

---------------------------------------

=

Given:

= 3.0V +10%

= +125°C

=+55°C

Find:

1. Actual power dissipation

2. Maximum allowable dissipation

–

=

3.0 1.1

×

()

2.7 0.975

×

()

–

[]40 10

3

–

×

220

--------------------------------------------------------------------------------------------

=

26.7mW

=

–

---------------------------------------

=

125 55

–

220

---------------------

=

318mW

=