LM317A National Semiconductor, LM317A Datasheet - Page 6

• Manufacturer Part Number: LM317A
• Description: 3-Terminal Adjustable Regulator
• Manufacturer: National Semiconductor

www.national.com
Application Hints
less and 10 µF capacitance. Figure 3 shows an LM117 with
protection diodes included for use with outputs greater than
25V and high values of output capacitance.
D1 protects against C1
D2 protects against C2
When a value for
a heatsink must be selected that has a value that is less than
or equal to this number.
in the catalog, or shown in a curve that plots temperature rise
vs power dissipation for the heatsink.
HEATSINKING TO-263, SOT-223 AND TO-252 PACKAGE
PARTS
The TO-263 (“S”), SOT-223 (“MP”) and TO-252 (”DT”) pack-
ages 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 4 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.
(H−A)
FIGURE 4.
FIGURE 3. Regulator with Protection Diodes
is specified numerically by the heatsink manufacturer
(J−A)
(H−A)
TO-263 Package
vs Copper (1 ounce) Area for the
is found using the equation shown,
(Continued)
(J−A)
DS009063-55
DS009063-7
for the TO-263
(J−A)
6
As a design aid, Figure 5 shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming
mum junction temperature is 125˚C).
Figure 6 and Figure 7 show the information for the SOT-223
package. Figure 7 assumes a
copper and 51˚C/W for 2 ounce copper and a maximum
junction temperature of 125˚C.
FIGURE 5. Maximum Power Dissipation vs T
FIGURE 7. Maximum Power Dissipation vs T
FIGURE 6.
(J−A)
the SOT-223 Package
the TO-263 Package
SOT-223 Package
vs Copper (2 ounce) Area for the
(J−A)
(J−A)
is 35˚C/W and the maxi-
of 74˚C/W for 1 ounce
DS009063-57
DS009063-56
DS009063-58
AMB
AMB
for
for