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LM1117-3.3-223 View Datasheet(PDF) - First Components International

Part Name
Description
Manufacturer
LM1117-3.3-223
Fci
First Components International Fci
LM1117-3.3-223 Datasheet PDF : 14 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
LM1117 800mA Low-dropout Linear Regulator
APPLICATION NOTE (Continued)
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, TR(max):
TR(max)=TJ(max)-TA(max)
where TJ(max) is the maximum allowable junction tempera-
ture (125˚C), and TA(max) is the maximum ambient tem-
perature which will be encountered in the application.
Using the calculated values for TR(max) and PD, the maxi-
mum allowable value for the junction-to-ambient thermal re-
sistance (θJA) can be calculated:
θJA = TR(max)/PD
If the maximum allowable value for θJA is found to be
136˚C/W for SOT-223 package or 79˚C/W for TO-220
package or 92˚C/W 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 θJA
falls below these limits, a heatsink is required.
As a design aid, Table 1 shows the value of the θJA of SOT-
223 and TO-252 for different heatsink area. The copper pat-
terns that we used to measure these θJAs are shown at 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 (in2)
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.
Layout
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TABLE 1. θJA Different Heatsink Area
Copper Area
Thermal Resistance
Top Side (in2)*
0.0123
Bottom Side (in2)
0
(θJA,˚C/W) SOT-223
136
(θJA,˚C/W) TO-252
103
0.066
0
123
87
0.3
0
84
60
0.53
0
75
54
0.76
0
69
52
1
0
66
47
0
0.2
115
84
0
0.4
98
70
0
0.6
89
63
0
0.8
82
57
0
1
79
57
0.066
0.066
125
89
0.175
0.175
93
72
0.284
0.284
83
61
0.392
0.392
75
55
0.5
0.5
70
53
*Tab of device attached to topside copper
FIGURE 7. θJA vs. 1oz Copper Area for SOT-223
FIGURE 8. θJA vs. 2oz Copper Area for TO-252
10
 

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