LM317MDTX

更新时间： 2024-02-03 20:34:42

品牌	Logo	应用领域
美国国家半导体 - NSC		稳压器
页数	文件大小	规格书
25页	732K
描述
3-Terminal Adjustable Regulator

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技术参数
数据手册

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LM317MDTX 技术参数

生命周期：	Contact Manufacturer	包装说明：	,
Reach Compliance Code：	unknown	风险等级：	5.59
Base Number Matches：	1

LM317MDTX 数据手册

Application Hints (Continued)

when either the input or output is shorted. Internal to the

LM117 is a 50Ω resistor which limits the peak discharge

current. No protection is needed for output voltages of 25V

or less and 10µF capacitance. Figure 3 shows an LM117

with protection diodes included for use with outputs greater

than 25V and high values of output capacitance.

00906355

FIGURE 4. θ_(J−A)vs Copper (1 ounce) Area for the

TO-263 Package

00906307

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 32˚C/W.

As a design aid, Figure 5 shows the maximum allowable

power dissipation compared to ambient temperature for the

TO-263 device (assuming θ_(J−A)is 35˚C/W and the maxi-

mum junction temperature is 125˚C).

D1 protects against C1

D2 protects against C2

FIGURE 3. Regulator with Protection Diodes

When a value for θ_(H−A)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_(H−A)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, SOT-223 AND TO-252 PACKAGE

PARTS

The TO-263 (“S”), SOT-223 (“MP”) and TO-252 (”DT”) pack-

ages 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 4 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.

00906356

FIGURE 5. Maximum Power Dissipation vs T_AMBfor

the TO-263 Package

Figure 6 and Figure 7 show the information for the SOT-223

package. Figure 7 assumes a θ_(J−A)of 74˚C/W for 1 ounce

copper and 51˚C/W for 2 ounce copper and a maximum

junction temperature of 125˚C.

www.national.com

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