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參數(shù)資料
| 型號： | LM3940J |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Cap-Free, NMOS, 150mA Low Dropout Regulator with Reverse Current Protection |
| 中文描述： | 無電容，NMOS管，150mA的低壓差穩(wěn)壓器的反向電流保護 |
| 文件頁數(shù)： | 6/11頁 |
| 文件大?。?/td> | 291K |
| 代理商： | LM3940J |
Application Hints
(Continued)
If a manufactured heatsink is to be selected, the value of
heatsink-to-ambient thermal resistance,
θ
(HA)
, must first be
calculated:
θ
(HA)
=
θ
(JA)
θ
(CH)
θ
(JC)
Where:
θ
(JC)
is defined as the thermal resistance from
the junction to the surface of the case. A
value of 4C/W can be assumed for
θ
(JC)
for this calculation.
θ
(CH)
is defined as the thermal resistance be-
tween the case and the surface of the heat-
sink. The value of
θ
will vary from
about 1.5C/W to about 2.5C/W (depend-
ing on method of attachment, insulator,
etc.). If the exact value is unknown, 2C/W
should be assumed for
θ
(CH)
.
When a value for
θ
is found using the equation shown,
a heatsink must be selected that has a value that is less than
or equal to this number.
θ
is specified numerically by the heatsink manufacturer
in the catalog, or shown in a curve that plots temperature rise
vs power dissipation for the heatsink.
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 package to the plane.
Figure 3shows for the TO-263 the measured values of
θ
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
(JA)
for the TO-263
package mounted to a PCB is 32C/W.
As a design aid, Figure 4 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).
Figure 5 and Figure 6 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 temperature of 125C.
Please see AN1028 for power enhancement techniques to
be used with the SOT-223 package.
DS012080-7
FIGURE 3.
θ
(JA)
vs Copper (1 ounce) Area for the
TO-263 Package
DS012080-8
FIGURE 4. Maximum Power Dissipation vs T
AMB
for
the TO-263 Package
DS012080-11
FIGURE 5.
θ
(JA)
vs Copper (2 ounce) Area for the
SOT-223 Package
DS012080-12
FIGURE 6. Maximum Power Dissipation vs T
AMB
for
the SOT-223 Package
www.national.com
6
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM3940J/WG-3.3 WAF | 制造商:Texas Instruments 功能描述: |
| LM3940J-3.3-QML | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1A Low Dropout Regulator for 5V to 3.3V Conversion |
| LM3940J-3.3-SCD | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Texas Instruments 功能描述: |
| LM3940LD-3.3/NOPB | 功能描述:IC REG LDO 3.3V 1A 8-LLP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 系列:- 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- 穩(wěn)壓器拓撲結構:正，固定式 輸出電壓:3.1V 輸入電壓:最高 5.5V 電壓 - 壓降（標準）:- 穩(wěn)壓器數(shù)量:1 電流 - 輸出:300mA 電流 - 限制（最?。?420mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-5 細型，TSOT-23-5 供應商設備封裝:TSOT-23-5 包裝:帶卷 (TR) |
| LM3940LDX-3.3 | 功能描述:IC REG LDO 3.3V 1A 8-LLP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 系列:- 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- 穩(wěn)壓器拓撲結構:正，固定式 輸出電壓:3.1V 輸入電壓:最高 5.5V 電壓 - 壓降（標準）:- 穩(wěn)壓器數(shù)量:1 電流 - 輸出:300mA 電流 - 限制（最?。?420mA 工作溫度:-40°C ~ 85°C 安裝類型:表面貼裝 封裝/外殼:SOT-23-5 細型，TSOT-23-5 供應商設備封裝:TSOT-23-5 包裝:帶卷 (TR) |
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