LM2937-25 National Semiconductor, LM2937-25 Datasheet - Page 7

• Manufacturer Part Number: LM2937-25
• Description: 400mA and 500mA Voltage Regulators
• Manufacturer: National Semiconductor

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
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
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
mum junction temperature is 125˚C).
Figure 5 and Figure 6 show the information for the SOT-223
package. Figure 6 assumes a
copper and 51˚C/W for 2 ounce copper and a maximum
junction temperature of 125˚C.
(H−A)
FIGURE 4. Maximum Power Dissipation vs T
FIGURE 3.
is specified numerically by the heatsink manufacturer
(J−A)
the TO-263 Package
vs Copper (1 ounce) Area for the
TO-263 Package
(J−A)
(J−A)
is 35˚C/W and the maxi-
of 74˚C/W for 1 ounce
DS100113-20
(J−A)
DS100113-21
for the TO-263
AMB
for
(J−A)
7
Please see AN1028 for power enhancement techniques to
be used with the SOT-223 package.
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.
FIGURE 6. Maximum Power Dissipation vs T
FIGURE 5.
(J−A)
the SOT-223 Package
SOT-223 Package
vs Copper (2 ounce) Area for the
DS100113-22
DS100113-23
www.national.com
AMB
for