LM2940IMP-10 [NSC]
1A Low Dropout Regulator; 1A低压降稳压器
| 型号： | LM2940IMP-10 |
| 厂家： | 
National Semiconductor |
| 描述： | 1A Low Dropout Regulator |
| 文件： | 总19页 (文件大小：500K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
January 2003
LM2940/LM2940C
1A Low Dropout Regulator
General Description
momentarily exceed the specified maximum operating volt-
age, the regulator will automatically shut down to protect
both the internal circuits and the load. The LM2940/
LM2940C cannot be harmed by temporary mirror-image in-
sertion. Familiar regulator features such as short circuit and
thermal overload protection are also provided.
The LM2940/LM2940C positive voltage regulator features
the ability to source 1A of output current with a dropout
voltage of typically 0.5V and a maximum of 1V over the
entire temperature range. Furthermore, a quiescent current
reduction circuit has been included which reduces the
ground current when the differential between the input volt-
age and the output voltage exceeds approximately 3V. The
quiescent current with 1A of output current and an input-
output differential of 5V is therefore only 30 mA. Higher
quiescent currents only exist when the regulator is in the
dropout mode (VIN − VOUT ≤ 3V).
Features
@
n Dropout voltage typically 0.5V IO = 1A
n Output current in excess of 1A
n Output voltage trimmed before assembly
n Reverse battery protection
Designed also for vehicular applications, the LM2940/
LM2940C and all regulated circuitry are protected from re-
verse battery installations or 2-battery jumps. During line
transients, such as load dump when the input voltage can
n Internal short circuit current limit
n Mirror image insertion protection
n P+ Product Enhancement tested
Typical Application
00882203
*
Required if regulator is located far from power supply filter.
**
C
must be at least 22 µF to maintain stability. May be increased without bound to maintain regulation during transients. Locate as close as possible
OUT
to the regulator. This capacitor must be rated over the same operating temperature range as the regulator and the ESR is critical; see curve.
Ordering Information
Temperature
Range
Output Voltage
9.0
Package
5.0
8.0
10
12
15
0˚C ≤ TJ ≤ 125˚C LM2940CT-5.0
LM2940CT-9.0
LM2940CS-9.0
LM2940CT-12
LM2940CS-12
LM2940CT-15
LM2940CS-15
LM2940LD-15
TO-220
TO-263
LM2940CS-5.0
−40˚C ≤ TJ
≤
LM2940LD-5.0
LM2940LD-8.0 LM2940LD-9.0
LM2940LD-10 LM2940LD-12
LLP 1k
Units
Tape and
Reel
125˚C
LM2940LDX-5.0
LM2940LDX-8.0 LM2940LDX-9.0
LM2940LDX-10 LM2940LDX-12 LM2940LDX-15
LLP 4.5k
Units
Tape and
Reel
−40˚C ≤ TJ
≤
≤
LM2940T-5.0
LM2940S-5.0
LM2940T-8.0
LM2940S-8.0
LM2940T-9.0
LM2940S-9.0
LM2940T-10
LM2940S-10
LM2940T-12
LM2940S-12
TO-220
125˚C
TO-263
−40˚C ≤ TJ
LM2940IMP-5.0 LM2940IMP-8.0 LM2940IMP-9.0 LM2940IMP-10 LM2940IMP-12 LM2940IMP-15
SOT-223
85˚C
LM2940IMPX-5.0 LM2940IMPX-8.0 LM2940IMPX-9.0 LM2940IMPX-10 LM2940IMPX-12 LM2940IMPX-15 SOT-223
in Tape
and Reel
SOT-223
Package Marking
L53B
L54B
L0EB
L55B
L56B
L70B
The physical size of the SOT-223 is too small to contain the full device part number. The package markings indicated are what will appear on the actual device.
© 2003 National Semiconductor Corporation
DS008822
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Ordering Information (Continued)
Temperature
Range
Output Voltage
Package
J16A
5.0
8.0
12
15
−55˚C ≤ TJ ≤ 125˚C
LM2940J-5.0/883
5962-8958701EA
LM2940WG5.0/883
5962-8958701XA
LM2940J-8.0/883
LM2940J-12/883
5962-9088401QEA
LM2940J-15/883
5962-9088501QEA
5962-9088301QEA
WG16A
For information on military temperature range products, please go to the Mil/Aero Web Site at http://www.national.com/appinfo/milaero/index.html.
Connection Diagrams
(TO-220) Plastic Package
3-Lead SOT-223
00882202
00882242
Front View
Front View
Order Part Number LM2940IMP-5.0,
LM2940IMP-8.0, LM2940IMP-9.0,
Order Number LM2940CT-5.0, LM2940CT-9.0,
LM2940CT-12, LM2940CT-15, LM2940T-5.0,
LM2940T-8.0, LM2940T-9.0,
LM2940IMP-10, LM2940IMP-12 or LM2940IMP-15
See NS Package Number MP04A
LM2940T-10 or LM2940T-12
See NS Package Number TO3B
16-Lead Ceramic Surface-Mount Package (WG)
16-Lead Dual-in-Line Package (J)
00882244
Top View
00882243
Top View
Order Number LM2940WG5.0/883 (5962-8958701XA)
See NS Package Number WG16A
Order Number LM2940J-5.0/883 (5962-8958701EA),
LM2940J-8.0/883 (5962-9088301QEA),
LM2940J-12/883 (5962-9088401QEA),
LM2940J-15/883 (5962-9088501QEA)
See NS Package Number J16A
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2
Connection Diagrams (Continued)
(TO-263) Surface-Mount Package
8-Lead LLP
00882211
Top View
00882212
Side View
00882246
Order Number LM2940CS-5.0, LM2940CS-9.0,
LM2940CS-12, LM2940CS-15,
LM2940S-5.0, LM2940S-8.0,
LM2940S-9.0, LM2940S-10 or LM2940S-12
See NS Package Number TS3B
Top View
Order Number LM2940LD-5.0, LM2940LD-8.0,
LM2940LD-9.0, LM2940LD-10,
LM2940LD-12, LM2940LD-15
See NS Package Number LDC08A
Pin 2 and pin 7 are fused to center DAP
Pin 5 ans 6 need to be tied together on PCB board
3
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Absolute Maximum Ratings (Note 1)
SOT-223 (MP) Package
260˚C, 4s
2 kV
ESD Susceptibility (Note 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Conditions (Note 1)
Input Voltage
LM2940S, T, MP ≤ 100 ms
LM2940CS, T ≤ 1 ms
60V
45V
26V
Temperature Range
Internal Power Dissipation
(Note 2)
LM2940T, LM2940S
LM2940CT, LM2940CS
LM2940IMP
−40˚C ≤ TJ ≤ 125˚C
0˚C ≤ TJ ≤ 125˚C
Internally Limited
150˚C
Maximum Junction Temperature
Storage Temperature Range
−40˚C ≤ TJ ≤ 85˚C
−55˚C ≤ TJ ≤ 125˚C
−40˚C ≤ TJ ≤ 125˚C
−65˚C ≤ TJ ≤ +150˚C
LM2940J, LM2940WG
LM2940LD
Lead Temperature, Time for Wave Soldering
TO-220 (T) Package
260˚C, 10s
260˚C, 4s
TO-263 (S) Package
Electrical Characteristics
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
5V
LM2940
8V
LM2940
LM2940/883
Limit
LM2940/883
Limit
Units
Parameter Conditions
Typ
Limit
Typ
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
6.25V ≤ VIN ≤ 26V
9.4V ≤ VIN ≤ 26V
Output Voltage
Line Regulation
Load Regulation
5 mA ≤ IO ≤ 1A
5.00
20
4.85/4.75
5.15/5.25
50
4.85/4.75
8.00
20
7.76/7.60
8.24/8.40
80
7.76/7.60
VMIN
VMAX
5.15/5.25
40/50
8.24/8.40
50/80
VO + 2V ≤ VIN ≤ 26V,
IO = 5 mA
mVMAX
50 mA ≤ IO ≤ 1A
LM2940, LM2940/883
LM2940C
35
35
50/80
50/100
55
55
80/130
80/130
mVMAX
50
80
Output
100 mADC and
20 mArms,
Impedance
35
1000/1000
55
1000/1000
mΩ
fO = 120 Hz
Quiescent
Current
VO +2V ≤ VIN ≤ 26V,
IO = 5 mA
LM2940, LM2940/883
LM2940C
10
10
30
15/20
15
15/20
50/60
10
30
15/20
45/60
15/20
50/60
mAMAX
mAMAX
µVrms
VIN = VO + 5V,
IO = 1A
45/60
Output Noise
Voltage
10 Hz − 100 kHz,
IO = 5 mA
150
700/700
240
1000/1000
Ripple Rejection
fO = 120 Hz, 1 Vrms
IO = 100 mA
LM2940
,
72
72
60/54
66
66
54/48
dBMIN
dBMIN
LM2940C
60
54
fO = 1 kHz, 1 Vrms
,
60/50
54/48
IO = 5 mA
Long Term
Stability
20
32
mV/
1000 Hr
VMAX
Dropout Voltage
IO = 1A
0.5
0.8/1.0
0.7/1.0
0.5
0.8/1.0
0.7/1.0
IO = 100 mA
(Note 6)
110
150/200
150/200
110
150/200
150/200
mVMAX
Short Circuit
Current
1.9
1.6
1.5/1.3
1.9
1.6
1.6/1.3
AMIN
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4
Electrical Characteristics (Continued)
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
5V
LM2940
8V
LM2940
LM2940/883
Limit
LM2940/883
Limit
Units
Parameter Conditions
Typ
Limit
Typ
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
Maximum Line
Transient
RO = 100Ω
LM2940, T ≤ 100 ms
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
RO = 100Ω
75
55
60/60
75
55
60/60
VMIN
40/40
40/40
45
45
Reverse Polarity
DC Input Voltage
LM2940, LM2940/883
LM2940C
−30
−30
−15/−15
−15/−15
−30
−30
−15/−15
−15/−15
VMIN
−15
−15
Reverse Polarity
Transient Input
Voltage
RO = 100Ω
LM2940, T ≤ 100 ms
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
−75
−55
−50/−50
−45/−45
−75
−50/−50
VMIN
−45/−45
−45/−45
Electrical Characteristics
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
9V
10V
LM2940
Limit
LM2940
Limit
Units
Parameter
Conditions
Typ
Typ
(Note 4)
(Note 4)
10.5V ≤ VIN ≤ 26V
11.5V ≤ VIN ≤ 26V
Output Voltage
Line Regulation
Load Regulation
5 mA ≤ IO ≤1A
9.00
8.73/8.55
9.27/9.45
90
10.00
9.70/9.50
10.30/10.50
100
VMIN
VMAX
VO + 2V ≤ VIN ≤ 26V,
IO = 5 mA
20
20
65
65
mVMAX
50 mA ≤ IO ≤ 1A
LM2940
60
60
90/150
100/165
mVMAX
LM2940C
90
Output Impedance
100 mADC and
20 mArms,
60
mΩ
fO = 120 Hz
<
Quiescent
Current
VO +2V ≤ VIN 26V,
IO = 5 mA
LM2940
10
10
15/20
15
10
15/20
45/60
mAMAX
LM2940C
VIN = VO + 5V, IO = 1A
10 Hz − 100 kHz,
IO = 5 mA
30
45/60
30
mAMAX
µVrms
Output Noise
Voltage
270
300
Ripple Rejection
fO = 120 Hz, 1 Vrms
IO = 100 mA
LM2940
,
64
64
34
52/46
63
36
51/45
dBMIN
LM2940C
52
Long Term
Stability
mV/
1000 Hr
VMAX
Dropout Voltage
IO = 1A
0.5
0.8/1.0
0.5
0.8/1.0
IO = 100 mA
110
150/200
110
150/200
mVMAX
5
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Electrical Characteristics (Continued)
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
Parameter Conditions
Short Circuit
9V
10V
LM2940
Limit
LM2940
Limit
Units
Typ
Typ
(Note 4)
1.6
(Note 4)
1.6
(Note 6)
1.9
1.9
AMIN
Current
Maximum Line
Transient
RO = 100Ω
T ≤ 100 ms
LM2940
75
55
60/60
75
60/60
VMIN
LM2940C
RO = 100Ω
LM2940
45
Reverse Polarity
DC Input Voltage
−30
−30
−15/−15
−30
−15/−15
VMIN
LM2940C
RO = 100Ω
T ≤ 100 ms
LM2940
−15
Reverse Polarity
Transient Input
Voltage
−75
−55
−50/−50
−45/−45
−75
−50/−50
VMIN
LM2940C
Electrical Characteristics
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
12V
LM2940
15V
LM2940
LM2940/833
Limit
LM2940/833
Limit
Units
Parameter Conditions
Typ
Limit
Typ
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
13.6V ≤ VIN ≤ 26V
12.00 11.64/11.40 11.64/11.40 15.00 14.55/14.25 14.55/14.25
12.36/12.60 12.36/12.60 15.45/15.75 15.45/15.75
16.75V ≤ VIN ≤ 26V
Output Voltage
Line Regulation
Load Regulation
5 mA ≤ IO ≤1A
VMIN
VMAX
VO + 2V ≤ VIN ≤ 26V,
IO = 5 mA
20
120
75/120
20
150
95/150
150/240
mVMAX
50 mA ≤ IO ≤ 1A
LM2940, LM2940/883
LM2940C
55
55
120/200
120/190
mVMAX
120
70
150
Output
100 mADC and
20 mArms,
Impedance
80
1000/1000
100
1000/1000
mΩ
fO = 120 Hz
Quiescent
Current
VO +2V ≤ VIN ≤ 26V,
IO = 5 mA
LM2940, LM2940/883
LM2940C
10
10
15/20
15
15/20
15/20
mAMAX
10
30
15
VIN = VO + 5V, IO = 1A
10 Hz − 100 kHz,
IO = 5 mA
30
45/60
50/60
45/60
50/60
mAMAX
µVrms
Output Noise
Voltage
360
1000/1000
450
1000/1000
Ripple Rejection
fO = 120 Hz, 1 Vrms
IO = 100 mA
LM2940
,
66
66
54/48
dBMIN
dBMIN
LM2940C
54
64
52
fO = 1 kHz, 1 Vrms
,
52/46
48/42
IO = 5 mA
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6
Electrical Characteristics (Continued)
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
Parameter Conditions
Long Term
12V
LM2940
15V
LM2940
LM2940/833
Limit
LM2940/833
Limit
Units
Typ
Limit
Typ
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
mV/
1000 Hr
VMAX
48
60
Stability
Dropout Voltage
IO = 1A
0.5
0.8/1.0
0.7/1.0
0.5
0.8/1.0
0.7/1.0
IO = 100 mA
(Note 6)
110
150/200
150/200
110
150/200
150/200
mVMAX
Short Circuit
Current
1.9
1.6
1.6/1.3
1.9
1.6
1.6/1.3
AMIN
Maximum Line
Transient
RO = 100Ω
LM2940, T ≤ 100 ms
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
RO = 100Ω
75
55
60/60
40/40
40/40
VMIN
45
55
45
Reverse Polarity
DC Input
LM2940, LM2940/883
LM2940C
−30
−30
−15/−15
−15/−15
−15/−15
VMIN
Voltage
−15
−30
−15
Reverse Polarity
Transient Input
Voltage
RO = 100Ω
LM2940, T ≤ 100 ms
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
−75
−55
−50/−50
−45/−45
−45/−45
−45/−45
VMIN
−55
−45/−45
Thermal Performance
Thermal Resistance
3-Lead TO-220
4
˚C/W
˚C/W
˚C/W
˚C/W
˚C/W
Junction-to-Case
3-Lead TO-263
4
Thermal Resistance
Junction-to-Ambient
3-Lead TO-220
60
80
35
3-Lead TO-263
8-Lead LLP (Note 2)
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Conditions are conditions under which the device functions
but the specifications might not be guaranteed. For guaranteed specifications and test conditions see the Electrical Characteristics.
Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, T , the junction-to-ambient thermal resistance, θ , and the
J
JA
ambient temperature, T . Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown.
A
The value of θ (for devices in still air with no heatsink) is 60˚C/W for the TO-220 package, 80˚C/W for the TO-263 package, and 174˚C/W for the SOT-223 package.
JA
The effective value of θ can be reduced by using a heatsink (see Application Hints for specific information on heatsinking). The value of θ for the LLP package
JA
JA
is specifically dependent on PCB trace area, trace material, and the number of layers and thermal vias. For improved thermal resistance and power dissipation for
the LLP package, refer to Application Note AN-1187. It is recommended that 6 vias be placed under the center pad to improve thermal performance.
Note 3: ESD rating is based on the human body model, 100 pF discharged through 1.5 kΩ.
Note 4: All limits are guaranteed at T = T = 25˚C only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type).
A
J
All limits at T = T = 25˚C are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control
A
J
methods.
Note 5: All limits are guaranteed at T = T = 25˚C only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type).
A
J
All limits are 100% production tested and are used to calculate Outgoing Quality Levels.
Note 6: Output current will decrease with increasing temperature but will not drop below 1A at the maximum specified temperature.
7
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Typical Performance Characteristics
Dropout Voltage
Dropout Voltage vs. Temperature
00882213
00882214
Output Voltage vs. Temperature
Quiescent Current vs. Temperature
00882215
00882216
Quiescent Current
Quiescent Current
00882217
00882218
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8
Typical Performance Characteristics (Continued)
Line Transient Response
Load Transient Response
Low Voltage Behavior
Low Voltage Behavior
00882220
00882219
Ripple Rejection
00882225
00882221
Low Voltage Behavior
00882226
00882227
9
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Typical Performance Characteristics (Continued)
Low Voltage Behavior
Low Voltage Behavior
Output at Voltage Extremes
Output at Voltage Extremes
00882228
00882229
00882231
00882233
Low Voltage Behavior
00882230
Output at Voltage Extremes
00882232
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Typical Performance Characteristics (Continued)
Output at Voltage Extremes
Output at Voltage Extremes
00882234
00882235
Output at Voltage Extremes
Output Capacitor ESR
00882236
00882206
Peak Output Current
Output Impedance
00882222
00882208
11
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Typical Performance Characteristics (Continued)
Maximum Power Dissipation (TO-220)
Maximum Power Dissipation (TO-3)
00882224
00882223
Maximum Power Dissipation (TO-263)
See (Note 2)
00882210
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12
Equivalent Schematic Diagram
00882201
Application Hints
Output Capacitor ESR
EXTERNAL CAPACITORS
The output capacitor is critical to maintaining regulator sta-
bility, and must meet the required conditions for both ESR
(Equivalent Series Resistance) and minimum amount of ca-
pacitance.
MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain sta-
bility is 22 µF (this value may be increased without limit).
Larger values of output capacitance will give improved tran-
sient response.
ESR LIMITS:
The ESR of the output capacitor will cause loop instability if
it is too high or too low. The acceptable range of ESR plotted
versus load current is shown in the graph below. It is essen-
tial that the output capacitor meet these requirements,
or oscillations can result.
00882206
FIGURE 1. ESR Limits
It is important to note that for most capacitors, ESR is
specified only at room temperature. However, the designer
must ensure that the ESR will stay inside the limits shown
over the entire operating temperature range for the design.
For aluminum electrolytic capacitors, ESR will increase by
about 30X as the temperature is reduced from 25˚C to
−40˚C. This type of capacitor is not well-suited for low tem-
perature operation.
Solid tantalum capacitors have a more stable ESR over
temperature, but are more expensive than aluminum elec-
trolytics. A cost-effective approach sometimes used is to
13
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HEATSINKING TO-220 PACKAGE PARTS
Application Hints (Continued)
parallel an aluminum electrolytic with a solid Tantalum, with
the total capacitance split about 75/25% with the Aluminum
being the larger value.
The TO-220 can be attached to a typical heatsink, or se-
cured to a copper plane on a PC board. If a copper plane is
to be used, the values of θ(JA) will be the same as shown in
the next section for the TO-263.
If two capacitors are paralleled, the effective ESR is the
parallel of the two individual values. The “flatter” ESR of the
Tantalum will keep the effective ESR from rising as quickly at
low temperatures.
If a manufactured heatsink is to be selected, the value of
heatsink-to-ambient thermal resistance, θ(H−A), must first be
calculated:
θ(H−A) = θ(JA) − θ(C−H) − θ(J−C)
Where: θ(J−C) is defined as the thermal resistance from the
junction to the surface of the case. A value of
3˚C/W can be assumed for θ(J−C) for this
calculation.
HEATSINKING
A heatsink may be required depending on the maximum
power dissipation and maximum ambient temperature of the
application. Under all possible operating conditions, the junc-
tion temperature must be within the range specified under
Absolute Maximum Ratings.
θ(C−H) is defined as the thermal resistance between
the case and the surface of the heatsink. The
value of θ(C−H) will vary from about 1.5˚C/W to
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
To determine if a heatsink is required, the power dissipated
by the regulator, PD, must be calculated.
The figure below shows the voltages and currents which are
present in the circuit, as well as the formula for calculating
the power dissipated in the regulator:
θ(C−H)
.
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 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.
00882237
I
= I ÷ I
L G
IN
Figure 3 shows for the TO-263 the measured values of θ(JA)
for different copper area sizes using a typical PCB with 1
ounce copper and no solder mask over the copper area used
for heatsinking.
P
= (V − V
) I + (V ) I
OUT L IN G
D
IN
FIGURE 2. Power Dissipation Diagram
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, TR (max). This is calcu-
lated by using the formula:
TR (max) = TJ(max) − TA (max)
where: TJ (max) is the maximum allowable junction tem-
perature, which is 125˚C for commercial
grade parts.
TA (max) is the maximum ambient temperature
which will be encountered in the
application.
Using the calculated values for TR(max) and PD, the maxi-
mum allowable value for the junction-to-ambient thermal
resistance, θ(JA), can now be found:
θ(JA) = TR (max)/PD
00882238
IMPORTANT: If the maximum allowable value for θ(JA) is
found to be ≥ 53˚C/W for the TO-220 package, ≥ 80˚C/W for
the TO-263 package, or ≥174˚C/W for the SOT-223 pack-
age, no heatsink is needed since the package alone will
dissipate enough heat to satisfy these requirements.
FIGURE 3. θ(JA) vs. Copper (1 ounce) Area for the
TO-263 Package
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 32˚C/W.
If the calculated value for θ(JA)falls below these limits, a
heatsink is required.
As a design aid, Figure 4 shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming θ(JA) is 35˚C/W and the maximum
junction temperature is 125˚C).
www.national.com
14
Application Hints (Continued)
00882240
00882239
FIGURE 5. θ(JA) vs. Copper (2 ounce) Area for the
SOT-223 Package
FIGURE 4. Maximum Power Dissipation vs. TAMB for
the TO-263 Package
Figure 5 and Figure 6 show the information for the SOT-223
package. Figure 6 assumes a θ(JA) of 74˚C/W for 1 ounce
copper and 51˚C/W for 2 ounce copper and a maximum
junction temperature of 125˚C.
00882241
FIGURE 6. Maximum Power Dissipation vs. TAMB for the SOT-223 Package
15
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted
3-Lead SOT-223 Package
Order Part Number LM2940IMP-5.0
LM2940IMP-8.0 LM2940IMP-9.0
LM2940IMP-10 LM2940IMP-12 LM2940IMP-15
NS Package Number MP04A
16 Lead Dual-in-Line Package (J)
Order Number LM2940J-5.0/883 (5962-8958701EA),
LM2940J-8.0/883 (5962-9088301QEA),
LM2940J-12/883 (5962-9088401QEA),
LM2940J-15/883 (5962-9088501QEA)
See NS Package Number J16A
www.national.com
16
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16 Lead Surface Mount Package (WG)
Order Number LM2940WG5.0/883 (5962-8958701XA)
See NS Package Number WG16A
3-Lead TO-220 Plastic Package (T)
Order Number LM2940T-5.0, LM2940T-8.0,
LM2940T-9.0, LM2940T-10, LM2940T-12, LM2940CT-5.0,
LM2940CT-12 or LM2940CT-15
NS Package Number TO3B
17
www.national.com
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
3-Lead TO-263 Surface Mount Package (MP)
Order Number LM2940S-5.0, LM2940S-8.0,
LM2940S-9.0, LM2940S-10, LM2940S-12,
LM2940CS-5.0, LM2940CS-12 or LM2940CS-15
NS Package Number TS3B
8-Lead LLP
Order Number LM2940LD-5.0, LM2940LD-8.0,
LM2940LD-9.0, LM2940LD-10,
LM2940LD-12 or LM2940LD-15
NS Package Number LDC08A
www.national.com
18
Notes
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
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Support Center
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Fax: +49 (0) 180-530 85 86
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Email: new.feedback@nsc.com
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Tel: 81-3-5639-7560
www.national.com
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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