LP3881 datasheet(10/12 Pages) NSC

10 / 12 page

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

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

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

ture is 125˚C.

HEATSINKING PSOP PACKAGE

Heatsinking for the PSOP-8 package is accomplished by

allowing heat to flow through the ground slug on the bottom

of the package into the copper on the PC board. The heat

slug must be soldered down to a copper plane to get good

heat transfer. It can also be connected through vias to inter-

nal copper planes. Since the heat slug is at ground potential,

traces must not be routed under it which are not at ground

potential. Under all possible conditions, the junction tem-

perature must be within the range specified under operating

conditions.

Figure 3 shows a curve for the

JA of the PSOP package for

different copper area sizes using a typical PCB with one

ounce copper in still air.

20063026

FIGURE 2. Maximum power dissipation vs ambient

temperature for TO-263 package

20063054

FIGURE 3.

JA vs. Copper (1 ounce) Area for PSOP

Package

LP3881 Scheda tecnica(PDF) 10 Page - National Semiconductor (TI)