REG1117
REG1117A
www.ti.com
SBVS001D − OCTOBER 1992 − REVISED JULY 2004
The SOT-223 package derives heat sinking from
conduction through its copper leads, especially the large
mounting tab. These must be soldered to a circuit board
with a substantial amount of copper remaining, as shown
in Figure 5. Circuit board traces connecting the tab and the
leads should be made as large as practical. The mounting
tab of both packages is electrically connected to V
OUT
.
Table 1. SOT-223
q
JA
for Various Board
Configurations
SOT-223
THERMAL
RESISTANCE
JUNCTION-
TO-AMBIENT
46°C/W
47°C/W
49°C/W
51°C/W
53°C/W
55°C/W
58°C/W
59°C/W
67°C/W
72°C/W
85°C/W
TOTAL PC
BOARD
AREA
2500mm2
2500mm2
TOPSIDE(1)
COPPER
AREA
2500mm2
1250mm2
950mm2
2500mm2
1800mm2
600mm2
1250mm2
915mm2
600mm2
340mm2
340mm2
BACKSIDE
COPPER
AREA
2500mm2
2500mm2
2500mm2
0
0
1600mm2
0
0
0
900mm2
0
Total Area: 50 x 50mm
2500mm2
2500mm2
2500mm2
1600mm2
2500mm2
2500mm2
1600mm2
900mm2
900mm2
35 x 17 mm
16 x 10 mm
16 x 10 mm
Without backside copper:
q
With solid backside copper:
q
JA
≈
59_ C/W
JA
≈
49_C/W
(1) Tab is attached to the topside copper.
Figure 5. SOT-223 Circuit Board Layout Example
SOLDERING METHODS
Other nearby circuit traces, including those on the back
side of the circuit board, help conduct heat away from the
device, even though they may not be electrically
connected. Make all nearby copper traces as wide as
possible and leave only narrow gaps between traces.
Table 1 shows approximate values of
q
JA
for various circuit
board and copper areas for the SOT-223 package. Nearby
heat dissipating components, circuit board mounting
conditions, and ventilation can dramatically affect the
actual
q
JA
. Proper heat sinking significantly increases the
maximum power dissipation at a given ambient
temperature, as shown in Figure 6.
Both REG1117 packages are suitable for infrared reflow
and vapor-phase reflow soldering techniques. The high
rate of temperature change that occurs with wave
soldering or hand soldering can damage the REG1117.
INSPEC Abstract Number: B91007604, C91012627.
Kelly, E.G. “Thermal Characteristics of Surface 5WK9Ω
Packages.” The Proceedings of SMTCON. Surface Mount
Technology Conference and Exposition: Competitive
Surface Mount Technology, April 3−6, 1990, Atlantic City,
NJ, USA. Abstract Publisher: IC Manage, 1990, Chicago,
IL, USA.
MAXIMUM POWER DISSIPATION
vs AMBIENT TEMPERATURE
6
5
4
3
2
1
0
0
25
50
75
100
125
Ambient Temperature (_ C)
q
JA
= 65
_
C/W
(no heat sink)
q
JA
= 85
_
C/W
(340mm
2
topside copper,
no backside copper)
q
JA
= 27
_
C/W
(4in
2
one oz copper
mounting pad)
q
JA
= 46
_
C/W
(2500mm
2
topside and
backside copper)
Power Dissipation (Watts)
P
D
= (T
J
(max)
−
T
A
) /
q
JA
T
J
(max) = 150_ C
DDPAK
SOT−223
Figure 6. Maximum Power Dissipation versus Ambient Temperature
10
BURR-BROWN [ BURR-BROWN CORPORATION ]
