LP3963_03 Datasheet, PDF (15/17 Pages) National Semiconductor (TI) – 3A Fast Ultra Low Dropout Linear Regulators

Application Hints (Continued)
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. Figure 3 shows a curve for the
θ_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 θ_JA for the TO-263 package 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 θ_JA is 35˚C/W and the maximum junction tempera-
ture is 125˚C.
10126732
FIGURE 3. θ_JA vs Copper (1 Ounce) Area for TO-263
package
10126733
FIGURE 4. Maximum power dissipation vs ambient
temperature for TO-263 package
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