Datasheet

LP3875-ADJ
www.ti.com SNVS247D –SEPTEMBER 2003–REVISED APRIL 2013
In this equation, θ
CH
is the thermal resistance from the case to the surface of the heat sink and θ
JC
is the thermal
resistance from the junction to the surface of the case. θ
JC
is about 3°C/W for a TO-220 package. The value for
θ
CH
depends on method of attachment, insulator, etc. θ
CH
varies between 1.5°C/W to 2.5°C/W. If the exact value
is unknown, 2°C/W can be assumed.
HEATSINKING DDPAK/TO-263 PACKAGE
The DDPAK/TO-263 package uses the copper plane on the PCB as a heatsink. The tab of these packages are
soldered to the copper plane for heat sinking. Figure 17 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 17. θ
JA
vs Copper (1 Ounce) Area for DDPAK/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 DDPAK/TO-263 package mounted to a PCB is 32°C/W.
Figure 18 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 18. Maximum Power Dissipation vs Ambient Temperature for DDPAK/TO-263 Package
HEATSINKING SOT-223-5 PACKAGE
Figure 19 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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