Datasheet

-40 -25 25
75 125
MAX POWER DISSIPATION (W)
AMBIENT TEMPERATURE (°C)
0
1
2
3
4
5
TO-263 PACKAGE
PCB MOUNT
1 SQ. IN. COPPER
0
1 2 3
COPPER FOIL AREA (SQ. IN.)
20
30
40
50
60
70
80
THERMAL RESISTANCE T
JA
(°C/W)
LMH6321
SNOSAL8C –APRIL 2006–REVISED MARCH 2013 www.ti.com
Examining Figure 54, we see that we cannot attain this low of a thermal resistance for one layer of 1 oz copper.
It will be necessary to derate the part by decreasing either the ambient temperature or the power dissipation.
Other solutions are to use two layers of 1 oz foil, or use 2 oz copper (see Table 1), or to provide forced air flow.
One should allow about an extra 15% heat sinking capability for safety margin.
Figure 54. Thermal Resistance (typ) for 7-L DDPAK Package Mounted on 1 oz. (0.036 mm) PC Board Foil
Figure 55. Derating Curve for DDPAK package. No Air Flow
Table 1. θ
JA
vs. Copper Area and P
D
for DDPAK. 1.0 oz cu Board. No Air Flow. Ambient Temperature =
24°C
Copper Area θJA @ 1.0W θJA @ 2.0W
(°C/W) (°C/W)
1 Layer = 1”x2” cu Bottom 62.4 54.7
2 Layer = 1”x2” cu Top & Bottom 36.4 32.1
2 Layer = 2”x2” cu Top & Bottom 23.5 22.0
2 Layer = 2”x4” cu Top & Bottom 19.8 17.2
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