LP3876-ADJ Datasheet, PDF (12/19 Pages) National Semiconductor (TI) – 3A Fast Ultra Low Dropout Linear Regulator

LP3876-ADJ
SNVS245C – SEPTEMBER 2003 – REVISED APRIL 2013
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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/DDPAK/TO-263 PACKAGE
The DDPAK/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 22 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 22. 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 23 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 23. Maximum power dissipation vs ambient temperature for DDPAK/TO-263 package
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