LM317A National Semiconductor, LM317A Datasheet - Page 7

• Manufacturer Part Number: LM317A
• Description: 3-Terminal Adjustable Regulator
• Manufacturer: National Semiconductor

Application Hints
The LM317 regulators have internal thermal shutdown to
protect the device from over-heating. Under all possible op-
erating conditions, the junction temperature of the LM317
must be within the range of 0˚C to 125˚C. A heatsink may be
required depending on the maximum power dissipation and
maximum ambient temperature of the application. To deter-
mine if a heatsink is needed, the power dissipated by the
regulator, P
Figure 8 shows the voltage and currents which are present in
the circuit.
Note:
I
P
IN
D
Layout
*
= I
= (V
Tab of device attached to topside of copper.
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
L
FIGURE 8. Power Dissipation Diagram
+ I
IN
D
G
, must be calculated:
− V
OUT
) I
L
+ V
Top Side (in
IN
I
G
0.0123
(Continued)
0.066
0.066
0.175
0.284
0.392
0.53
0.76
0.3
0.5
1
0
0
0
0
0
2
)*
Copper Area
TABLE 1.
DS009063-60
JA
Bottom Side (in
Different Heatsink Area
7
0.066
0.175
0.284
0.392
0.2
0.4
0.6
0.8
0.5
0
0
0
0
0
0
1
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T
where T
ture (125˚C), and T
perature which will be encountered in the application.
Using the calculated values for T
mum allowable value for the junction-to-ambient thermal re-
sistance (
If the maximum allowable value for
heatsink is needed since the package alone will dissipate
enough heat to satisfy these requirements. If the calculated
value for
As a design aid, Table 1 shows the value of the
TO-252 for different heatsink area. The copper patterns that
we used to measure these
Application Notes Section. Figure 9 reflects the same test re-
sults as what are in the Table 1
Figure 10 shows the maximum allowable power dissipation
vs. ambient temperature for the TO-252 device. Figure 11
shows the maximum allowable power dissipation vs. copper
area (in
power enhancement techniques to be used with SOT-223
and TO-252 packages.
92˚C/W (Typical Rated Value) for TO-252 package, no
T
JA
R
(max) = T
2
= T
)
2
J
) for the TO-252 device. Please see AN1028 for
(max) is the maximum allowable junction tempera-
R
JA
JA
(max)/P
) can be calculated:
falls below these limits, a heatsink is required.
J
(max) − T
D
A
Thermal Resistance
(max) is the maximum ambient tem-
(
JA
A
˚C/W) TO-252
(max)
JA
103
s are shown at the end of the
87
60
54
52
47
84
70
63
57
57
89
72
61
55
53
R
(max) and P
R
(max):
JA
is found to be
D
www.national.com
, the maxi-
JA
of