LM3940
SNVS114E –MAY 1999–REVISED MARCH 2013
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Figure 21. θ(JA) vs. Copper (1 ounce) Area for the DDPAK/TO-263 Package
As shown in Figure 21, increasing the copper area beyond 1 square inch produces very little improvement. It
should also be observed that the minimum value of θ(JA) for the DDPAK/TO-263 package mounted to a PCB is
32°C/W.
As a design aid, Figure 22 shows the maximum allowable power dissipation compared to ambient temperature
for the DDPAK/TO-263 device (assuming θ(JA) is 35°C/W and the maximum junction temperature is 125°C).
Figure 22. Maximum Power Dissipation vs. TAMB for the DDPAK/TO-263 Package
Figure 23 and Figure 24 show the information for the SOT-223 package. Figure 24 assumes a θ(JA) of 74°C/W
for 1 ounce copper and 51°C/W for 2 ounce copper and a maximum junction temperature of 125°C.
Figure 23. θ(JA) vs. Copper (2 ounce) Area for the SOT-223 Package
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