LP3962 datasheet(16/22 Pages) NSC

16 / 22 page

Applications Information (Continued)

Heatsinking TO-263 and SOT-223 Packages

The TO-263 and SOT223 packages use the copper plane on

the PCB as a heatsink. The tab of these packages are

soldered to the copper plane for heat sinking.

Figure 3

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.

As shown in the figure, increasing the copper area beyond 1

square inch produces very little improvement. The minimum

value for

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

32˚C/W.

Figure 4 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.

Figure 5 shows a curve for the

JA of SOT-223 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.

The following figures show different layout scenarios for

SOT-223 package.

10126632

FIGURE 3.

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

package

10126633

FIGURE 4. Maximum power dissipation vs ambient

temperature for TO-263 package

10126619

FIGURE 5.

JA vs Copper(1 Ounce) Area for SOT-223

package

10126620

FIGURE 6. SCENARIO A,

JA = 148˚C/W

10126621

FIGURE 7. SCENARIO B,

JA = 125˚C/W

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