LM1117I National Semiconductor Corporation, LM1117I Datasheet - Page 11

• Manufacturer Part Number: LM1117I
• Description: 800ma Low-dropout Linear Regulator
• Manufacturer: National Semiconductor Corporation

APPLICATION NOTE
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 (
If the maximum allowable value for
package or 92˚C/W for TO-252 package, no heatsink is
*Tab of device attached to topside copper
136˚C/W for SOT-223 package or
T
JA
R
Layout
(max)=T
= T
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
J
(max) is the maximum allowable junction tempera-
R
(max)/P
JA
J
(max)-T
) can be calculated:
D
A
(max) is the maximum ambient tem-
Top Side (in
A
(max)
0.0123
0.066
0.066
0.175
0.284
0.392
0.53
0.76
0.3
0.5
1
0
0
0
0
0
R
2
(max) and P
R
)*
Copper Area
(Continued)
(max):
79˚C/W for TO-220
JA
TABLE 1.
is found to be
Bottom Side (in
D
, the maxi-
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
JA
Different Heatsink Area
2
11
)
needed since the package alone will dissipate enough heat
to satisfy these requirements. If the calculated value for
falls below these limits, a heatsink is required.
As a design aid, Table 1 shows the value of the
SOT-223 and TO-252 for different heatsink area. The copper
patterns that we used to measure these
the end of the Application Notes Section. Figure 7 and Figure
8 reflects the same test results as what are in the Table 1
Figure 9 and Figure 10 shows the maximum allowable power
dissipation vs. ambient temperature for the SOT-223 and
TO-252 device. Figures Figure 11 and Figure 12 shows the
maximum allowable power dissipation vs. copper area (in
for the SOT-223 and TO-252 devices. Please see AN1028
for power enhancement techniques to be used with SOT-223
and TO-252 packages.
(
JA
,˚C/W) SOT-223
136
123
115
125
84
75
69
66
98
89
82
79
93
83
75
70
Thermal Resistance
(
JA
,˚C/W) TO-252
JA
103
s are shown at
87
60
54
52
47
84
70
63
57
57
89
72
61
55
53
www.national.com
JA
JA
of
2
)