LM317AMDT National Semiconductor, LM317AMDT Datasheet - Page 9

• Manufacturer Part Number: LM317AMDT
• Description: IC, ADJ LINEAR REG, 1.2V TO 37V, TO252-3
• Manufacturer: National Semiconductor

Specifications of LM317AMDT

• Primary Input Voltage: 40V
• Dropout Voltage Vdo: 2V
• No. Of Outputs: 1
• No. Of Pins: 3
• Output Current: 500mA
• Operating Temperature Range: -40°C To +125°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application Hints
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.
D1 protects against C1
D2 protects against C2
When a value for θ
a heatsink must be selected that has a value that is less than
or equal to this number.
θ
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
for different copper area sizes using a typical PCB with 1
ounce copper and no solder mask over the copper area used
for heatsinking.
(H−A)
FIGURE 3. Regulator with Protection Diodes
is specified numerically by the heatsink manufacturer
(H−A)
is found using the equation shown,
(Continued)
00906307
(J−A)
9
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
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
mum junction temperature is 125˚C).
Figure 6 and Figure 7 show the information for the SOT-223
package. Figure 7 assumes a θ
copper and 51˚C/W for 2 ounce copper and a maximum
junction temperature of 125˚C.
FIGURE 5. Maximum Power Dissipation vs T
FIGURE 4. θ
(J−A)
the TO-263 Package
TO-263 Package
vs Copper (1 ounce) Area for the
(J−A)
(J−A)
is 35˚C/W and the maxi-
of 74˚C/W for 1 ounce
(J−A)
00906355
for the TO-263
00906356
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AMB
for