LP38853 Datasheet, PDF (14/18 Pages) Texas Instruments – LP38853 3A Fast-Response High-Accuracy Adjustable LDO Linear Regulator with Enable and Soft-Start

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, insula-
tor, etc. θ_CH varies between 1.5°C/W to 2.5°C/W. Consult the
heat-sink manufacturer datasheet for details and recommen-
dations.
Heat-Sinking The TO-263 Package
The 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 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. Figure 3 shows a curve for the θ_JA of
TO-263 package for different copper area sizes, using a typ-
ical PCB with 1 ounce copper and no solder mask over the
copper area for heat-sinking.
ing θ_JA is 35°C/W and the maximum junction temperature is
125°C.
Heat-Sinking The PSOP-8 Package
The LP38853MR package has a θ_JA rating of 168°C/W, and
a θ_JC rating of 11°C/W. The θ_JA rating of 168°C/W includes
the device DAP soldered to an area of 0.008 square inches
(0.09 in x 0.09 in) of 1 ounce copper, with no airflow.
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FIGURE 3. θ_JA vs Copper (1 Ounce) Area for the TO-263
package
Figure 3 shows that increasing the copper area beyond 1
square inch produces very little improvement. The minimum
value for θ_JA for the TO-263 package mounted to a PCB is
32°C/W.
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FIGURE 5. θ_JA vs Copper (1 Ounce) Area for the PSOP-8
Package
Increasing the copper area soldered to the DAP to 1 square
inch of 1 ounce copper, using a dog-bone type layout, will
improve the θ_JA rating to 98°C/W. Figure 5 shows that in-
creasing the copper area beyond 1 square inch produces very
little improvement.
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FIGURE 4. Maximum Power Dissipation vs Ambient
Temperature for the TO-263 Package
Figure 4 shows the maximum allowable power dissipation for
TO-263 packages for different ambient temperatures, assum-
20131028
FIGURE 6. Maximum Power Dissipation vs Ambient
Temperature for the PSOP-8 Package
Figure 6 shows the maximum allowable power dissipation for
the PSOP-8 package for a range of ambient temperatures,
assuming θ_JA is 98°C/W and the maximum junction temper-
ature is 125°C.
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