LP3891

SNVS235D – SEPTEMBER 2003 – REVISED APRIL 2013

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Figure 19.

θJA vs Copper (1 Ounce) Area for DDPAK/TO-263 Package

As shown in Figure 20, increasing the copper area beyond 1 square inch produces very little improvement. The

minimum value for

θJA for the DDPAK/TO-263 package mounted to a PCB is 32°C/W.

Figure 20 shows the maximum allowable power dissipation for DDPAK/TO-263 packages for different ambient

temperatures, assuming

θJA is 35°C/W and the maximum junction temperature is 125°C.

Figure 20. Maximum Power Dissipation vs Ambient Temperature for DDPAK/TO-263 Package

HEATSINKING SO PowerPAD PACKAGE

Heatsinking for the SO PowerPAD-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 internal 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 temperature must be within the range specified under operating conditions.

Figure 21 shows a curve for the

θJA of the SO PowerPAD package for different copper area sizes using a typical

PCB with one ounce copper in still air.

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