Datasheet

LP3883

www.ti.com

SNVS223F –NOVEMBER 2002–REVISED APRIL 2013

= T

Rmax

/ P

(6)

These parts are available in TO-220 and DDPAK/TO-263 packages. The thermal resistance depends on amount

of copper area or heat sink, and on air flow. If the maximum allowable value of θ

calculated above is ≥ 60 °C/W

for TO-220 package and ≥ 60 °C/W for DDPAK/TO-263 package no heatsink is needed since the package can

dissipate enough heat to satisfy these requirements. If the value for allowable θ

falls below these limits, a heat

sink is required.

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

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

− θ

. (7)

In this equation, θ

is the thermal resistance from the case to the surface of the heat sink and θ

is the thermal

resistance from the junction to the surface of the case. θ

is about 3°C/W for a TO220 package. The value for

depends on method of attachment, insulator, etc. θ

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/TO-263 PACKAGE

The 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. The graph below shows a curve for the θ

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 34. θ

vs Copper (1 Ounce) Area for DDPAK/TO-263 package

As shown in the graph below, increasing the copper area beyond 1 square inch produces very little improvement.

The minimum value for θ

for the DDPAK/TO-263 package mounted to a PCB is 32°C/W.

Figure 35 shows the maximum allowable power dissipation for DDPAK/TO-263 packages for different ambient

temperatures, assuming θ

is 35°C/W and the maximum junction temperature is 125°C.

Figure 35. Maximum power dissipation vs ambient temperature for DDPAK/TO-263 package

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