board copper area. Increasing the copper area improves heat
dissipation. Figure 12 shows typical thermal resistance from
junction to ambient as a function of the copper area for the
DDPAK.
Power dissipation depends on input voltage and load condi-
tions. Power dissipation is equal to the product of the
average output current times the voltage across the output
element, VIN to VOUT voltage drop.
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 REG103 devices
are presented in the Application Bulletin “Solder Pad Rec-
ommendations for Surface-Mount Devices” (SBFA015),
available from the Texas Instruments web site (www.ti.com).
PD = (VIN – VOUT ) • IOUT(AVG)
Power dissipation can be minimized by using the lowest
possible input voltage necessary to assure the required
output voltage.
REGULATOR MOUNTING
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-
THERMAL RESISTANCE vs PCB COPPER AREA
50
Circuit-Board Copper Area
REG103
40
30
20
10
0
Surface-Mount Package
1 oz. copper
θ
REG103
DDPAK Surface-Mount Package
5
0
1
2
3
4
Copper Area (Inches2)
FIGURE 12. Thermal Resistance versus PCB Area for the Five-Lead DDPAK.
THERMAL RESISTANCE vs PCB COPPER AREA
180
Circuit-Board Copper Area
REG103
Surface-Mount Package
160
140
120
100
80
1 oz. copper
θ
60
40
20
REG103
SOT-223 Surface-Mount Package
0
0
1
2
3
4
5
Copper Area (Inches2)
FIGURE 13. Thermal Resistance versus PCB Area for the Five-Lead SOT-223.
REG103
12
SBVS010D
BB [ BURR-BROWN CORPORATION ]
