LM2937 datasheet(8/11 Pages) NSC

8 / 11 page

Application Hints (Continued)

(H−A) is specified numerically by the heatsink manufacturer

in the catalog, or shown in a curve that plots temperature rise

vs power dissipation for the heatsink.

HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS

Both the TO-263 (“S”) and SOT-223 (“MP”) packages use a

copper plane on the PCB and the PCB itself as a heatsink.

To optimize the heat sinking ability of the plane and PCB,

solder the tab of the package to the plane.

Figure 3 shows for the TO-263 the measured values of

(J−A)

for different copper area sizes using a typical PCB with 1

ounce copper

and no solder mask over the copper area used

for heatsinking.

As shown in the figure, increasing the copper area beyond 1

square inch produces very little improvement. It should also

be observed that the minimum value of

(J−A) for the TO-263

package mounted to a PCB is 32˚C/W.

As a design aid,

Figure 4 shows the maximum allowable

power dissipation compared to ambient temperature for the

TO-263 device (assuming

(J−A) is 35˚C/W and the maxi-

mum junction temperature is 125˚C).

Figure 5 and Figure 6 show the information for the SOT-223

package.

Figure 6 assumes a

(J−A) of 74˚C/W for 1 ounce

copper and 51˚C/W for 2 ounce copper and a maximum

junction temperature of 125˚C.

SOT-223 SOLDERING RECOMMENDATIONS

It is not recommended to use hand soldering or wave solder-

ing to attach the small SOT-223 package to a printed circuit

board. The excessive temperatures involved may cause

package cracking.

Either vapor phase or infrared reflow techniques are pre-

ferred soldering attachment methods for the SOT-223 pack-

age.

DS011280-28

FIGURE 3.

(J−A) vs Copper (1 ounce) Area for the

TO-263 Package

DS011280-29

FIGURE 4. Maximum Power Dissipation vs T

AMB for

the TO-263 Package

DS011280-30

FIGURE 5.

(J−A) vs Copper (2 ounce) Area for the

SOT-223 Package

DS011280-31

FIGURE 6. Maximum Power Dissipation vs T

AMB for

the SOT-223 Package

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