LM341-LM78M National Semiconductor, LM341-LM78M Datasheet - Page 7

• Manufacturer Part Number: LM341-LM78M
• Description: 3-Terminal Positive Voltage Regulators
• Manufacturer: National Semiconductor

Design Considerations
The LM78MXX/LM341XX regulators have internal thermal
shutdown to protect the device from over-heating. Under all
possible operating conditions, the junction temperature of
the LM78MXX/LM341XX must be within the range of 0˚C to
125˚C. A heatsink may be required depending on the maxi-
mum power dissipation and maximum ambient temperature
of the application. To determine if a heatsink is needed, the
power dissipated by the regulator, P
shows the voltages and currents which are present in the
circuit.
*
Mounted on a printed circuit board. Note that the case
temperature is measured at the point where the leads
Tab of device attached to topside copper
FIGURE 1. Cross-sectional view of Integrated Circuit
I
P
IN
D
= I
= (V
L
contact with the mounting pad surface
Layout
+ I
IN
10
11
12
13
14
15
16
−V
1
2
3
4
5
6
7
8
9
G
OUT
) I
L
+ V
IN
I
G
Top Sice (in
D
0.0123
0.066
0.066
0.175
0.284
0.392
, must be calculated:
0.53
0.76
0.3
0.5
1
0
0
0
0
0
(Continued)
TABLE 1.
2
)*
Copper Area
DS010484-23
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
If the maximum allowable value for
age, no heatsink is needed since the package alone will dis-
sipate enough heat to satisfy these requirements. If the cal-
culated value for
required.
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 Note Section. reflects the same test results as
what are in the Table 1
shows the maximum allowable power dissipation vs. ambi-
ent temperature for theTO-252 device. shows the maximum
allowable power dissipation vs. copper area (in
TO-252 device. Please see AN1028 for power enhancement
techniques to be used with TO-252 package.
60˚C/W for TO-220 package or 92˚C/W for TO-252 pack-
JA
= TR (max)/P
2
)
FIGURE 2. Power Dissipation Diagram
Thermal Resistance
(
JA
JA
D
, ˚C/W) TO-252
fall below these limits, a heatsink is
103
87
60
54
52
47
84
70
63
57
57
89
72
61
55
53
JA
are shown at the end of the
R
(max):
JA
˚C/w is found to be
DS010484-24
www.national.com
2
) for the
JA
of