Datasheet

LM2937
www.ti.com SNVS100E –MARCH 2000–REVISED APRIL 2013
HEATSINKING TO-220 PACKAGE PARTS
The TO-220 can be attached to a typical heatsink, or secured to a copper plane on a PC board. If a copper plane
is to be used, the values of θ
(J−A)
will be the same as shown in the next section for the DDPAK/TO-263.
If a manufactured heatsink is to be selected, the value of heatsink-to-ambient thermal resistance, θ
(H−A)
, must
first be calculated:
θ
(H−A)
= θ
(J−A)
− θ
(C−H)
− θ
(J−C)
where
• θ
(J−C)
is defined as the thermal resistance from the junction to the surface of the case. A value of 3°C/W can be
assumed for θ
(J−C)
for this calculation
• θ
(C−H)
is defined as the thermal resistance between the case and the surface of the heatsink. The value of
θ
(C−H)
will vary from about 1.5°C/W to about 2.5°C/W (depending on method of attachment, insulator, etc.). If
the exact value is unknown, 2°C/W should be assumed for θ
(C−H)
(3)
When a value for θ
(H−A)
is found using the equation shown, a heatsink must be selected that has a value that is
less than or equal to this number.
θ
(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 DDPAK/TO-263 AND SOT-223 PACKAGE PARTS
Both the DDPAK/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 26 shows for the DDPAK/TO-263 the measured values of θ
(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.
Figure 26. θ
(J−A)
vs. Copper (1 ounce) Area for the DDPAK/TO-263 Package
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 θ
(J−A)
for the DDPAK/TO-263 package mounted to a PCB is
32°C/W.
As a design aid, Figure 27 shows the maximum allowable power dissipation compared to ambient temperature
for the DDPAK/TO-263 device (assuming θ
(J−A)
is 35°C/W and the maximum junction temperature is 125°C).
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