LM2940S-12/NOPB National Semiconductor, LM2940S-12/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM2940S-12/NOPB
• Description: IC REGULATOR LDO 1A TO-263
• Manufacturer: National Semiconductor

Specifications of LM2940S-12/NOPB

• Regulator Topology: Positive Fixed
• Voltage - Output: 12V
• Voltage - Input: 13.6 ~ 26 V
• Voltage - Dropout (typical): 0.5V @ 1A
• Number Of Regulators: 1
• Current - Output: 1A
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TO-263-3, D²Pak (3 leads + Tab), TO-263AA
• Number Of Outputs: 1
• Polarity: Positive
• Input Voltage Max: 26 V
• Output Voltage: 12 V
• Output Type: Fixed
• Dropout Voltage (max): 0.8 V At 1 A
• Output Current: 1 A (Typ)
• Line Regulation: 120 mV
• Load Regulation: 120 mV
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Voltage Regulator Type: Linear
• Topology: LDO
• Regulator Output Type: Fixed
• Polarity Type: Positive
• Input Voltage (min): 13.6V
• Input Voltage (max): 26V
• Package Type: TO-263
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Dropout Voltage@current (typ): 0.5@1A/0.11@100mA
• Pin Count: 3 +Tab
• Mounting: Surface Mount
• Quiescent Current (max): 15mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Limit (min): -
• Lead Free Status / Rohs Status: Details
• Other names: *LM2940S-12; *LM2940S-12/NOPB; LM2940S-12

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θ
When a value for θ
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 PACKAGE PARTS
The TO-263 (“S”) package uses 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 3 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.
FIGURE 3. θ
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 4 shows the maximum allowable pow-
er dissipation compared to ambient temperature for the
TO-263 device. This assumes a θ
inch of 1 ounce copper and a maximum junction temperature
(T
(H−A)
J
) of 125°C.
is specified numerically by the heatsink manufacturer
(C−H)
(JA)
is defined as the thermal resistance between
the case and the surface of the heatsink. The
value of θ
about 2.5°C/W (depending on method of at-
tachment, insulator, etc.). If the exact value is
unknown, 2°C/W should be assumed for θ
−H)
vs. Copper (1 ounce) Area for the TO-263
.
(H−A)
is found using the equation shown, a
(C−H)
Package
will vary from about 1.5°C/W to
(JA)
of 35°C/W for 1 square
(JA)
for the TO-263
882238
(JA)
(C
14
HEATSINKING SOT-223 PACKAGE PARTS
The 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 5 and Figure 6 show the information for the SOT-223
package. Figure 6 assumes a θ
inch of 1 ounce copper and 51°C/W for 1 square inch of 2
ounce copper, with a maximum ambient temperature (T
85°C and a maximum junction temperature (T
For techniques for improving the thermal resistance and pow-
er dissipation for the SOT-223 package, please refer to Ap-
plication Note AN-1028.
FIGURE 5. θ
FIGURE 4. Maximum Power Dissipation vs. T
(JA)
vs. Copper (2 ounce) Area for the SOT-223
TO-263 Package
Package
(JA)
of 74°C/W for 1 square
882240
J
) of 125°C.
882239
A
for the
A
) of