LP2960 datasheet(13/17 Pages) NSC

13 / 17 page

Application Hints (Continued)

The next parameter which must be calculated is the maxi-

mum allowable temperature rise, T

R (max). This is calcu-

lated by using the formula:

R (max) = TJ (max) − TA (max)

where:

J (max) is the maximum allowable junction temperature,

which is 125˚C for commercial grade parts.

A (max) is the maximum ambient temperature which will be

encountered in the application.

Using the calculated values for T

R (max) and PD, the maxi-

mum allowable value for the junction-to-ambient thermal re-

sistance,

(J−A), can now be found:

(J−A) = TR (max)/PD

The heatsink for the LP2960 is made using the PC board

copper, with the heat generated on the die being conducted

through the lead frame and out to the pins which are sol-

dered to the PC board.

The GND pins are the only ones capable of conducting any

significant amount of heat, as they are internally attached to

the lead frame on which the die is mounted.

The figure below shows recommended copper foil patterns

to be used for heatsinking the DIP and Surface Mount pack-

ages:

The table below shows measured values of

(J−A) foraPC

board with 1 ounce copper weight:

Package

L (in.)

H (in.)

J−A(˚C/W)

DIP

0.5

0.2

Surface

Mount

0.5

0.2

As the heat must transfer from the copper to the surrounding

air, best results (lowest

J−A) will be obtained by using a sur-

face copper layer with the solder resist opened up over the

heatsink area.

If an

internal copper layer of a multi-layer board is used for

heatsinking, the board material acts as an insulator, inhibit-

ing heat transfer and increasing

J−A.

As with any heatsink, increasing the airflow across the board

will significantly improve the heat transfer.

Heat Sink Foil Patterns

DS011962-31

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