LM2937IMP-33 Datasheet, PDF (9/19 Pages) Texas Instruments – LM2937-2.5, LM2937-3.3 400mA and 500mA Voltage Regulators

LM2937-2.5, LM2937-3.3
www.ti.com
SNVS015E – FEBRUARY 1998 – REVISED APRIL 2013
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 (“KTT”) and SOT-223 (“DCY”) 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 25 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 25. 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 26 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).
Figure 26. Maximum Power Dissipation vs T_AMB for the DDPAK/TO-263 Package
Figure 27 and Figure 28 show the information for the SOT-223 package. Figure 28 assumes a θ_(J−A) of 74°C/W
for 1 ounce copper and 51°C/W for 2 ounce copper and a maximum junction temperature of +85°C.
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