參數(shù)資料
型號: LM78M15CH
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 基準(zhǔn)電壓源/電流源
英文描述: 5.0 AMP POSITIVE VOLTAGE REGULATOR
中文描述: 15 V FIXED POSITIVE REGULATOR, MBCY3
封裝: METAL CAN, TO-39, 3 PIN
文件頁數(shù): 7/11頁
文件大小: 310K
代理商: LM78M15CH
Design Considerations
(Continued)
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 0C to
125C. 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
D
, must be calculated:
I
IN
= I
L
+ I
G
P
D
= (V
IN
V
OUT
) I
L
+ V
IN
I
G
shows the voltages and currents which are present in the
circuit.
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T
R
(max):
θ
JA
= TR (max)/P
D
If the maximum allowable value for
θ
C/w is found to be
60C/W for TO-220 package or
92C/W for TO-252 pack-
age, no heatsink is needed since the package alone will dis-
sipate enough heat to satisfy these requirements. If the cal-
culated value for
θ
JA
fall below these limits, a heatsink is
required.
As a design aid, Table 1 shows the value of the
θ
of
TO-252 for different heatsink area. The copper patterns that
we used to measure these
θ
are shown at the end of the
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
2
) for the
TO-252 device. Please see AN1028 for power enhancement
techniques to be used with TO-252 package.
TABLE 1.
θ
JA
Different Heatsink Area
Layout
Copper Area
Thermal Resistance
(
θ
JA
, C/W) TO-252
103
87
60
54
52
47
84
70
63
57
57
89
72
61
55
53
Top Sice (in
2
)*
0.0123
0.066
0.3
0.53
0.76
1
0
0
0
0
0
0.066
0.175
0.284
0.392
0.5
Bottom Side (in
2
)
0
0
0
0
0
0
0.2
0.4
0.6
0.8
1
0.066
0.175
0.284
0.392
0.5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
*
Tab of device attached to topside copper
DS010484-23
FIGURE 1. Cross-sectional view of Integrated Circuit
Mounted on a printed circuit board. Note that the case
temperature is measured at the point where the leads
contact with the mounting pad surface
DS010484-24
FIGURE 2. Power Dissipation Diagram
www.national.com
7
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