LX8415 Microsemi Corporation, LX8415 Datasheet - Page 6

• Manufacturer Part Number: LX8415
• Description: 0.5a Low Dropout Positive Regulators
• Manufacturer: Microsemi Corporation

LX8415-xx
6
THERMAL CONSIDERATIONS (continued)
Example
Solution: The junction temperature is:
where: P
Given: V
Find: The size of a square area of 1oz. copper circuit-
I
R
board trace-foil that will serve as a heatsink,
adequate to maintain the junction temperature of the
LX8415 in the ST (SOT-223) package within
specified limits.
T
R
R
R
T
OUT
J
D
S
IN
JT
JT
TS
SA
= P
= 5.0V ±5%, V
= 15°C/W, R
= 0.5A, T
D
T
Dissipated power.
Thermal resistance from the junction to the
mounting tab of the package.
Thermal resistance through the interface
between the IC and the surface on which
it is mounted.
Thermal resistance from the mounting surface
of the heatsink to ambient.
Heat sink temperature.
J
(R
JT
R
+ R
JT
A
= 55°C, T
T
CS
C
TS
OUT
+ R
R
= 5°C/W
CS
= 2.5V ±3%
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
SA
0 . 5 A L
T
) + T
J
S
= 125°C
R
SA
A
P
T
R E L I M I N A R Y
A
O W
A P P L I C A T I O N N O T E S
D
R O P O U T
P
O S I T I V E
D
heat sink:
1 oz. copper circuit-board trace material. The following equation
describes the observed relationship between the area of a square
copper pad, and the thermal resistance from the tab of a SOT-223
package soldered at the center of the pad to ambient.
square pad with area:
within specified limits.
A T A
First, find the maximum allowable thermal resistance of the
A test was conducted to determine the thermal characteristics of
Substituting the value for R
will be required to maintain the LX8415 junction temperature
Area
P
P
R
Area
R
SINK
S
D
D
SA
E G U L A T O R S
H E E T
= 0.43 in
SINK
=
= 1.4W
=
[
T
[V
=
J
P
IN
- T
D
R
* (1 + Tol
A
SA
2
3.1°C/W
(0.66" x 0.66"), 280mm
- (R
- 22.3°C/W
SA
JT
VIN
+ R
calculated above, we find that a
)] - [V
TS
) ,
in
OUT
2
* (1 - Tol
R
SA
= 29.6°C/W
2
(17 x 17 mm)
VOUT
Copyright © 1999
)]
Rev. 0.4
]
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OUT
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