LP38855_15 Datasheet, PDF (12/20 Pages) Texas Instruments – 1.5A Fast-Response High-Accuracy LDO Linear Regulator with Enable

LP38855
SNVS461D – OCTOBER 2006 – REVISED APRIL 2013
www.ti.com
The heat-sink to be used in the application should have a heat-sink to ambient thermal resistance, θ_HA:
T_HA d T_JA - (T_CH + T_JC)
where
• θ_JA is the required total thermal resistance from the junction to the ambient air
• θ_CH is the thermal resistance from the case to the surface of the heat sink
• θ_JC is the thermal resistance from the junction to the surface of the case
(7)
For this equation, 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. Consult the heat-sink manufacturer
datasheet for details and recommendations.
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 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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