Datasheet

LP38856
SNVS336E –JUNE 2006–REVISED APRIL 2013 www.ti.com
Heat-Sinking The DDPAK/TO-263 Package
The DDPAK/TO-263 package has a θ
JA
rating of 60°C/W, and a θ
JC
rating of 3°C/W. These ratings are for the
package only, no additional heat-sinking, and with no airflow.
The DDPAK/TO-263 package uses the copper plane on the PCB as a heat-sink. The tab of this package is
soldered to the copper plane for heat-sinking. The graph below shows a curve for the θ
JA
of DDPAK/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.
Figure 27. θ
JA
vs Copper (1 Ounce) Area for the DDPAK/TO-263 package
As shown in Figure 27, increasing the copper area beyond 1 square inch produces very little improvement. The
minimum value for θ
JA
for the DDPAK/TO-263 package mounted to a PCB is 32°C/W.
Figure 28 shows the maximum allowable power dissipation for DDPAK/TO-263 packages for different ambient
temperatures, assuming θ
JA
is 35°C/W and the maximum junction temperature is 125°C.
Figure 28. Maximum Power Dissipation vs Ambient Temperature for DDPAK/TO-263 package
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