LP3891 Datasheet, PDF (10/12 Pages) National Semiconductor (TI) – 0.8A Fast-Response Ultra Low Dropout Linear

Application Hints (Continued)
As shown in the graph below, 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 2 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 2. Maximum power dissipation vs ambient
temperature for TO-263 package
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