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參數(shù)資料
| 型號： | LM340T127812 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3-Terminal Positive Regulators |
| 中文描述： | 三端正穩(wěn)壓器 |
| 文件頁數(shù)： | 12/17頁 |
| 文件大?。?/td> | 925K |
| 代理商： | LM340T127812 |
Application Hints
(Continued)
HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS
Both the TO-263 (“S”) and SOT-223 (“MP”) packages use a
copper plane on the PCB and the PCB itself as a heatsink.
To optimize the heat sinking ability of the plane and PCB,
solder the tab of the plane.
shows for the TO-263 the measured values of
θ
(J–A)
for
different copper area sizes using a typical PCB with 1 ounce
copper
and no solder mask over the copper area used for
heatsinking
.
As shown in the figure, increasing the copper area beyond 1
square inch produces very little improvement. It should also
be observed that the minimum value of
θ
(J–A)
for the TO-263
package mounted to a PCB is 32C/W.
As a design aid,
Figure 5
shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming
θ
is 35C/W and the maxi-
mum junction temperature is 125C).
Figures 6, 7
show the information for the SOT-223 package.
Figure 6
assumes a
θ
of 74C/W for 1 ounce copper and
51C/W for 2 ounce copper and a maximum junction tem-
perature of 125C.
Please see AN-1028 for power enhancement techniques to
be used with the SOT-223 package.
00778139
FIGURE 4.
θ
vs Copper (1 ounce)
Area for the TO-263 Package
00778140
FIGURE 5. Maximum Power Dissipation vs
T
AMB
for the TO-263 Package
00778141
FIGURE 6.
θ
(J–A)
vs Copper (2 ounce) Area
for the SOT-223 Package
00778142
FIGURE 7. Maximum Power Dissipation vs
T
AMB
for the SOT-223 Package
L
www.national.com
12
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