LP3962 Datasheet, PDF (16/22 Pages) National Semiconductor (TI) – 1.5A Fast Ultra Low Dropout Linear Regulators

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 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.
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FIGURE 5. θ_JA vs Copper(1 Ounce) Area for SOT-223
package
The following figures show different layout scenarios for
SOT-223 package.
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FIGURE 3. θ_JA vs Copper(1 Ounce) Area for TO-263
package
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 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 θ_JA is 35˚C/W and the maximum junction tempera-
ture is 125˚C.
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FIGURE 6. SCENARIO A, θ_JA = 148˚C/W
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FIGURE 7. SCENARIO B, θ_JA = 125˚C/W
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FIGURE 4. Maximum power dissipation vs ambient
temperature for TO-263 package
Figure 5 shows a curve for the θ_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.
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