LM883E NSC [National Semiconductor], LM883E Datasheet - Page 10

• Manufacturer Part Number: LM883E
• Description: 3-Terminal Adjustable Regulator
• Manufacturer: NSC [National Semiconductor]

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Application Hints
The LM317 regulators have internal thermal shutdown to
protect the device from over-heating. Under all possible
operating 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-
FIGURE 7. Maximum Power Dissipation vs T
FIGURE 6. θ
Layout
1
2
3
4
5
6
7
8
9
(J−A)
the SOT-223 Package
SOT-223 Package
vs Copper (2 ounce) Area for the
(Continued)
Top Side (in
0.0123
0.066
0.53
0.76
0.3
1
0
0
0
TABLE 1. θ
2
00906357
)*
00906358
Copper Area
AMB
for
JA
Different Heatsink Area
10
Bottom Side (in
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.
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
resistance (θ
If the maximum allowable value for θ
≥92˚C/W (Typical Rated Value) for TO-252 package, no
heatsink is needed since the package alone will dissipate
enough heat to satisfy these requirements. If the calculated
value for θ
As a design aid, Table 1 shows the value of the θ
TO-252 for different heatsink area. The copper patterns that
we used to measure these θ
Application Notes Section. Figure 9 reflects the same test
results 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.
I
P
T
θ
IN
JA
0.2
0.4
0.6
R
D
0
0
0
0
0
0
(max) = T
= I
= (V
= T
2
J
L
) for the TO-252 device. Please see AN1028 for
(max) is the maximum allowable junction tempera-
FIGURE 8. Power Dissipation Diagram
R
+ I
IN
JA
(max)/P
D
2
G
− V
, must be calculated:
JA
)
falls below these limits, a heatsink is required.
J
) can be calculated:
(max) − T
OUT
D
) I
A
(max) is the maximum ambient tem-
L
+ V
A
Thermal Resistance
(max)
IN
(θ
JA
I
G
JA
s are shown at the end of the
˚C/W) TO-252
R
(max) and P
R
103
87
60
54
52
47
84
70
63
(max):
JA
is found to be
D
, the maxi-
00906360
JA
of