LP3891 Datasheet, PDF (9/12 Pages) National Semiconductor (TI) – 0.8A Fast-Response Ultra Low Dropout Linear

Application Hints (Continued)
HEATSINKING TO-220 PACKAGE
The thermal resistance of a TO220 package can be reduced
by attaching it to a heat sink or a copper plane on a PC
board. If a copper plane is to be used, the values of θ_JA will
be same as shown in next section for TO263 package.
The heatsink to be used in the application should have a
heatsink to ambient thermal resistance,
θ_HA≤ θ_JA − θ_CH − θ_JC.
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 resis-
tance from the junction to the surface of the case. θ_JC is
about 3˚C/W for a TO220 package. The value for θ_CH de-
pends 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 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. 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.
20069525
FIGURE 1. θ_JA vs Copper (1 Ounce) Area for TO-263
package
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