LP3852_15 Datasheet, PDF (20/32 Pages) Texas Instruments – 1.5-A Fast Response Ultra-Low Dropout Linear Regulators

LP3852, LP3855
SNVS174I – FEBRUARY 2003 – REVISED FEBRUARY 2015
www.ti.com
Power Dissipation/Heatsinking (continued)
In this equation, R_θCH is the thermal resistance from the case to the surface of the heat sink, and R_θJC is the
thermal resistance from the junction to the surface of the case. R_θJC is about 3°C/W for a TO-220 package. The
value for R_θCH depends on method of attachment, insulator, etc. R_θCH varies between 1.5°C/W to 2.5°C/W. If the
exact value is unknown, 2°C/W can be assumed.
12.4.2 Heatsinking TO-263 Package
The 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 26 shows a curve for the R_θJA 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 26. R_θJA vs Copper (1 Ounce) Area for TO-263 package
As shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. The
minimum value for R_θJA for the TO-263 package mounted to a PCB is 32°C/W.
Figure 27 shows the maximum allowable power dissipation for TO-263 packages for different ambient
temperatures, assuming R_θJA is 35°C/W and the maximum junction temperature is 125°C.
Figure 27. Maximum Power Dissipation vs Ambient Temperature for TO-263 Package
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