LP38859 datasheet(12/14 Pages) NSC

12 / 14 page

Application Information (Continued)

(8)

where

JA is the required total thermal resistance from the

junction to the ambient air,

CH is the thermal resistance from

the case to the surface of the heart-sink, and

JC is the

thermal resistance from the junction to the surface of the

case.

For this equation,

JC is about 3˚C/W for a TO-220 package.

The value for

CH depends on method of attachment, insu-

lator, etc.

CH varies between 1.5˚C/W to 2.5˚C/W. Consult

the heat-sink manufacturer datasheet for details and recom-

mendations.

Heat-Sinking The TO-263 Package

The TO-263 package has a

JA rating of 60˚C/W, and a

rating of 3˚C/W. These ratings are for the package only, no

additional heat-sinking, and with no airflow.

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

a heat-sink. The tab of this package is soldered to the copper

plane for heat sinking. 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.

Figure 2 shows that increasing the copper area beyond 1

square inch produces very little improvement. The minimum

value for

JA for the TO-263 package mounted to a PCB is

32˚C/W.

Figure 3 shows the maximum allowable power dissipation

for TO-263 packages for different ambient temperatures,

assuming

JA is 35˚C/W and the maximum junction tempera-

ture is 125˚C.

20131225

FIGURE 2.

JA vs Copper (1 Ounce) Area for the

TO-263 package

20131226

FIGURE 3. Maximum power dissipation vs ambient

temperature for the TO-263 package

LP38859 数据表(PDF) 12 Page - National Semiconductor (TI)

LP38859 数据表(HTML) 12 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14

数据表下载