REGULATOR MOUNTING
Although the tabs of the DDPAK and the SOT-223 are
electrically grounded, they are not intended to carry any
current. The copper pad that acts as a heat sink should be
isolated from the rest of the circuit to prevent current flow
through the device from the tab to the ground pin. Solder pad
footprint recommendations for the various REG104 devices
are presented in the Application Bulletin Solder Pad Recom-
mendations for Surface-Mount Devices (SBFA015A), avail-
able from the Texas Instruments web site (www.ti.com).
The tab of both packages is electrically connected to ground.
For best thermal performance, the tab of the DDPAK sur-
face-mount version should be soldered directly to a circuit-
board copper area. Increasing the copper area improves
heat dissipation. Figure 10 shows typical thermal resistance
from junction to ambient as a function of the copper area for
the DDPAK. Figure 11 shows the same relationship for the
SOT-223.
THERMAL RESISTANCE vs PCB COPPER AREA
50
Circuit Board Copper Area
REG104
Surface Mount Package
40
30
20
10
0
1 oz. copper
REG104
DDPAK Surface Mount Package
5
0
1
2
3
4
Copper Area (inches2)
FIGURE 10. Thermal Resistance versus PCB Area for the Five-Lead DDPAK.
THERMAL RESISTANCE vs PCB COPPER AREA
180
Circuit Board Copper Area
REG104
Surface Mount Package
160
1 oz. copper
140
120
100
80
θ
60
40
20
REG104
SOT-223 Surface Mount Package
0
0
1
2
3
4
5
Copper Area (inches2)
FIGURE 11. Thermal Resistance versus PCB Area for the Five Lead SOT-223.
REG104
12
SBVS025G
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