LP3892 datasheet(9/12 Pages) NSC

9 / 12 page

Application Hints (Continued)

HEATSINKING TO-220 PACKAGE

The thermal resistance of a TO220 package can be reduced

by attaching it to a heat sink or a copper plane on a PC

board. If a copper plane is to be used, the values of

JA will

be same as shown in next section for TO263 package.

The heatsink to be used in the application should have a

heatsink to ambient thermal resistance,

≤θ

JA −

CH −

JC.

In this equation,

CH is the thermal resistance from the case

to the surface of the heat sink and

JC is the thermal resis-

tance from the junction to the surface of the case.

JC is

about 3˚C/W for a TO220 package. The value for

CH de-

pends on method of attachment, insulator, etc.

CH varies

between 1.5˚C/W to 2.5˚C/W. If the exact value is unknown,

2˚C/W can be assumed.

HEATSINKING TO-263 PACKAGE

The TO-263 package uses the copper plane on the PCB as

a heatsink. The tab of these packages are soldered to the

copper plane for heat sinking. The graph below shows a

curve for the

JA of TO-263 package for different copper area

sizes, using a typical PCB with 1 ounce copper and no solder

mask over the copper area for heat sinking.

20069625

FIGURE 1.

JA vs Copper (1 Ounce) Area for TO-263

package

LP3892 데이터시트(PDF) 9 Page - National Semiconductor (TI)