NSC LM2940T-10 1a low dropout regulator Datasheet

LM2940/LM2940C
1A Low Dropout Regulator
General Description
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 voltage and the output voltage exceeds approximately 3V. The
quiescent current with 1A of output current and an inputoutput differential of 5V is therefore only 30 mA. Higher
quiescent currents only exist when the regulator is in the
dropout mode (VIN − VOUT ≤ 3V).
Designed also for vehicular applications, the LM2940/
LM2940C and all regulated circuitry are protected from reverse battery installations or 2-battery jumps. During line
transients, such as load dump when the input voltage can
momentarily exceed the specified maximum operating voltage, 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 insertion. Familiar regulator features such as short circuit and
thermal overload protection are also provided.
Features
n
n
n
n
n
n
n
Dropout voltage typically 0.5V @IO = 1A
Output current in excess of 1A
Output voltage trimmed before assembly
Reverse battery protection
Internal short circuit current limit
Mirror image insertion protection
P+ Product Enhancement tested
Typical Application
00882203
*Required if regulator is located far from power supply filter.
**COUT must be at least 22 µF to maintain stability. May be increased without bound to maintain regulation during transients. Locate as close as possible
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
0˚C ≤ TJ ≤ 125˚C
−40˚C ≤ TJ ≤
125˚C
−40˚C ≤ TJ ≤
125˚C
−40˚C ≤ TJ ≤
85˚C
SOT-223
Package Marking
Output Voltage
5.0
8.0
9.0
10
12
Package
15
LM2940CT-5.0
LM2940CT-9.0
LM2940CT-12
LM2940CT-15
LM2940CS-5.0
LM2940CS-9.0
LM2940CS-12
LM2940CS-15
TO-263
LM2940LD-12
LM2940LD-15
LLP 1k
Units
Tape and
Reel
LM2940LDX-15
LLP 4.5k
Units
Tape and
Reel
LM2940LD-5.0
LM2940LD-8.0
LM2940LD-9.0
LM2940LD-10
LM2940LDX-5.0
LM2940LDX-8.0 LM2940LDX-9.0
LM2940LDX-10 LM2940LDX-12
LM2940T-5.0
LM2940T-8.0
LM2940T-9.0
LM2940T-10
LM2940T-12
LM2940S-5.0
LM2940S-8.0
LM2940S-9.0
LM2940S-10
LM2940S-12
LM2940IMP-5.0
LM2940IMP-8.0
LM2940IMP-9.0
LM2940IMP-10
LM2940IMP-12
TO-220
TO-263
LM2940IMP-15
LM2940IMPX-5.0 LM2940IMPX-8.0 LM2940IMPX-9.0 LM2940IMPX-10 LM2940IMPX-12 LM2940IMPX-15
L53B
L54B
L0EB
L55B
L56B
TO-220
SOT-223
SOT-223
in Tape
and Reel
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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LM2940/LM2940C 1A Low Dropout Regulator
January 2003
LM2940/LM2940C
Ordering Information
Temperature
Range
(Continued)
Output Voltage
5.0
−55˚C ≤ TJ ≤ 125˚C
8.0
LM2940J-5.0/883
5962-8958701EA
Package
12
LM2940J-8.0/883
5962-9088301QEA
15
LM2940J-12/883
5962-9088401QEA
LM2940J-15/883
5962-9088501QEA
LM2940WG5.0/883
5962-8958701XA
J16A
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
Order Number LM2940CT-5.0, LM2940CT-9.0,
LM2940CT-12, LM2940CT-15, LM2940T-5.0,
LM2940T-8.0, LM2940T-9.0,
LM2940T-10 or LM2940T-12
See NS Package Number TO3B
Front View
Order Part Number LM2940IMP-5.0,
LM2940IMP-8.0, LM2940IMP-9.0,
LM2940IMP-10, LM2940IMP-12 or LM2940IMP-15
See NS Package Number MP04A
16-Lead Ceramic Surface-Mount Package (WG)
16-Lead Dual-in-Line Package (J)
00882244
00882243
Top View
Order Number LM2940WG5.0/883 (5962-8958701XA)
See NS Package Number WG16A
Top View
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
LM2940/LM2940C
Connection Diagrams
(Continued)
(TO-263) Surface-Mount Package
8-Lead LLP
00882211
Top View
00882212
Side View
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
00882246
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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LM2940/LM2940C
Absolute Maximum Ratings
SOT-223 (MP) Package
(Note 1)
ESD Susceptibility (Note 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
LM2940S, T, MP ≤ 100 ms
60V
LM2940CS, T ≤ 1 ms
45V
2 kV
Operating Conditions (Note 1)
Input Voltage
26V
Temperature Range
Internal Power Dissipation
(Note 2)
Maximum Junction Temperature
Lead Temperature, Time for Wave Soldering
TO-263 (S) Package
260˚C, 4s
−40˚C ≤ TJ ≤ 85˚C
LM2940IMP
−65˚C ≤ TJ ≤ +150˚C
260˚C, 10s
0˚C ≤ TJ ≤ 125˚C
LM2940CT, LM2940CS
150˚C
TO-220 (T) Package
−40˚C ≤ TJ ≤ 125˚C
LM2940T, LM2940S
Internally Limited
Storage Temperature Range
260˚C, 4s
LM2940J, LM2940WG
−55˚C ≤ TJ ≤ 125˚C
LM2940LD
−40˚C ≤ TJ ≤ 125˚C
Electrical Characteristics
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating temperature range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
Parameter
Conditions
5V
Typ
8V
LM2940
LM2940/883
Limit
Limit
(Note 4)
(Note 5)
Typ
6.25V ≤ VIN ≤ 26V
Output Voltage
Line Regulation
5 mA ≤ IO ≤ 1A
4.85/4.75
4.85/4.75
5.15/5.25
5.15/5.25
20
50
40/50
LM2940, LM2940/883
35
50/80
50/100
LM2940C
35
50
VO + 2V ≤ VIN ≤ 26V,
5.00
LM2940
LM2940/883
Limit
Limit
(Note 4)
(Note 5)
Units
9.4V ≤ VIN ≤ 26V
8.00
7.76/7.60
7.76/7.60
VMIN
8.24/8.40
8.24/8.40
VMAX
20
80
50/80
mVMAX
55
80/130
80/130
mVMAX
55
80
1000/1000
mΩ
IO = 5 mA
Load Regulation
Output
Impedance
50 mA ≤ IO ≤ 1A
100 mADC and
20 mArms,
35
1000/1000
55
15/20
10
15/20
15/20
mAMAX
50/60
30
45/60
50/60
mAMAX
700/700
240
1000/1000
µVrms
fO = 120 Hz
Quiescent
VO +2V ≤ VIN ≤ 26V,
Current
IO = 5 mA
LM2940, LM2940/883
10
15/20
LM2940C
10
15
VIN = VO + 5V,
30
45/60
IO = 1A
Output Noise
10 Hz − 100 kHz,
Voltage
IO = 5 mA
Ripple Rejection
fO = 120 Hz, 1 Vrms,
150
IO = 100 mA
LM2940
72
60/54
LM2940C
72
60
fO = 1 kHz, 1 Vrms,
66
54/48
66
54
60/50
dBMIN
54/48
dBMIN
IO = 5 mA
Long Term
20
32
mV/
Stability
Dropout Voltage
Short Circuit
Current
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1000 Hr
IO = 1A
0.5
0.8/1.0
0.7/1.0
0.5
0.8/1.0
0.7/1.0
VMAX
IO = 100 mA
110
150/200
150/200
110
150/200
150/200
mVMAX
1.9
1.6
1.5/1.3
1.9
1.6
1.6/1.3
AMIN
(Note 6)
4
(Continued)
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating temperature range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
Parameter
Conditions
Maximum Line
RO = 100Ω
Transient
LM2940, T ≤ 100 ms
5V
Typ
75
8V
LM2940
LM2940/883
Limit
Limit
(Note 4)
(Note 5)
60/60
75
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
45
LM2940, LM2940/883
−30
−15/−15
LM2940C
−30
−15
−75
−50/−50
RO = 100Ω
DC Input Voltage
Reverse Polarity
RO = 100Ω
Transient Input
LM2940, T ≤ 100 ms
Voltage
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
LM2940/883
Limit
Limit
(Note 4)
(Note 5)
60/60
40/40
55
Reverse Polarity
Typ
LM2940
−15/−15
40/40
55
45
−30
−15/−15
−30
−15
−75
−50/−50
−45/−45
−55
−15/−15
Units
VMIN
VMIN
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 temperature range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
9V
10V
LM2940
Parameter
Conditions
Typ
Limit
LM2940
Typ
(Note 4)
10.5V ≤ VIN ≤ 26V
Output Voltage
5 mA ≤ IO ≤1A
Line Regulation
VO + 2V ≤ VIN ≤ 26V,
Load Regulation
50 mA ≤ IO ≤ 1A
9.00
8.73/8.55
Limit
Units
(Note 4)
11.5V ≤ VIN ≤ 26V
10.00
9.27/9.45
9.70/9.50
VMIN
10.30/10.50
VMAX
20
90
20
100
mVMAX
LM2940
60
90/150
65
100/165
mVMAX
LM2940C
60
90
IO = 5 mA
Output Impedance
100 mADC and
20 mArms,
60
65
mΩ
fO = 120 Hz
Quiescent
VO +2V ≤ VIN < 26V,
Current
IO = 5 mA
LM2940
10
15/20
LM2940C
10
15
VIN = VO + 5V, IO = 1A
30
45/60
Output Noise
10 Hz − 100 kHz,
270
Voltage
IO = 5 mA
Ripple Rejection
fO = 120 Hz, 1 Vrms,
10
15/20
mAMAX
30
45/60
mAMAX
300
µVrms
IO = 100 mA
LM2940
64
52/46
LM2940C
64
52
Long Term
Stability
Dropout Voltage
34
63
51/45
36
dBMIN
mV/
1000 Hr
IO = 1A
0.5
0.8/1.0
0.5
0.8/1.0
VMAX
IO = 100 mA
110
150/200
110
150/200
mVMAX
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LM2940/LM2940C
Electrical Characteristics
LM2940/LM2940C
Electrical Characteristics
(Continued)
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating temperature range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
9V
10V
LM2940
Parameter
Conditions
Typ
Limit
LM2940
Typ
(Note 4)
Short Circuit
(Note 6)
Units
Limit
(Note 4)
1.9
1.6
1.9
1.6
AMIN
LM2940
75
60/60
75
60/60
VMIN
LM2940C
55
45
−30
−15/−15
VMIN
−75
−50/−50
VMIN
Current
Maximum Line
RO = 100Ω
Transient
T ≤ 100 ms
Reverse Polarity
RO = 100Ω
DC Input Voltage
LM2940
−30
−15/−15
LM2940C
−30
−15
Reverse Polarity
RO = 100Ω
Transient Input
T ≤ 100 ms
Voltage
LM2940
−75
−50/−50
LM2940C
−55
−45/−45
Electrical Characteristics
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating temperature range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
Parameter
Conditions
12V
Typ
15V
LM2940
LM2940/833
Limit
Limit
(Note 4)
(Note 5)
Typ
13.6V ≤ VIN ≤ 26V
Output Voltage
5 mA ≤ IO ≤1A
11.64/11.40
11.64/11.40
12.36/12.60
12.36/12.60
20
120
75/120
LM2940, LM2940/883
55
120/200
120/190
LM2940C
55
120
Line Regulation
VO + 2V ≤ VIN ≤ 26V,
Load Regulation
50 mA ≤ IO ≤ 1A
12.00
LM2940
LM2940/833
Limit
Limit
(Note 4)
(Note 5)
Units
16.75V ≤ VIN ≤ 26V
15.00
20
14.55/14.25
14.55/14.25
VMIN
15.45/15.75
15.45/15.75
VMAX
150
95/150
mVMAX
150/240
mVMAX
1000/1000
mΩ
15/20
mAMAX
50/60
mAMAX
1000/1000
µVrms
IO = 5 mA
Output
100 mADC and
Impedance
20 mArms,
Quiescent
Current
VO +2V ≤ VIN ≤ 26V,
70
80
1000/1000
150
100
fO = 120 Hz
IO = 5 mA
LM2940, LM2940/883
Output Noise
10
15/20
LM2940C
10
15
VIN = VO + 5V, IO = 1A
30
45/60
10 Hz − 100 kHz,
360
Voltage
IO = 5 mA
Ripple Rejection
fO = 120 Hz, 1 Vrms,
15/20
10
15
50/60
30
45/60
1000/1000
450
IO = 100 mA
LM2940
66
54/48
LM2940C
66
54
dBMIN
64
fO = 1 kHz, 1 Vrms,
52/46
IO = 5 mA
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52
48/42
dBMIN
(Continued)
VIN = VO + 5V, IO = 1A, CO = 22 µF, unless otherwise specified. Boldface limits apply over the entire operating temperature range of the indicated device. All other specifications apply for TA = TJ = 25˚C.
Output Voltage (VO)
Parameter
12V
Conditions
Long Term
Short Circuit
LM2940/833
Limit
Limit
(Note 4)
(Note 5)
Typ
48
Stability
Dropout Voltage
Typ
15V
LM2940
LM2940
LM2940/833
Limit
Limit
(Note 4)
(Note 5)
Units
mV/
60
1000 Hr
IO = 1A
0.5
0.8/1.0
0.7/1.0
0.5
0.8/1.0
0.7/1.0
VMAX
IO = 100 mA
110
150/200
150/200
110
150/200
150/200
mVMAX
1.9
1.6
1.6/1.3
1.9
1.6
1.6/1.3
AMIN
75
60/60
40/40
VMIN
55
45
55
45
−15/−15
VMIN
−30
−15
−45/−45
VMIN
−55
−45/−45
(Note 6)
Current
Maximum Line
RO = 100Ω
Transient
LM2940, T ≤ 100 ms
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
40/40
Reverse Polarity
RO = 100Ω
DC Input
LM2940, LM2940/883
−30
−15/−15
Voltage
LM2940C
−30
−15
−75
−50/−50
−55
−45/−45
Reverse Polarity
RO = 100Ω
Transient Input
LM2940, T ≤ 100 ms
Voltage
LM2940/883, T ≤ 20 ms
LM2940C, T ≤ 1 ms
−15/−15
−45/−45
Thermal Performance
Thermal Resistance
Junction-to-Case
3-Lead TO-220
4
˚C/W
3-Lead TO-263
4
˚C/W
Thermal Resistance
Junction-to-Ambient
3-Lead TO-220
60
˚C/W
3-Lead TO-263
80
˚C/W
8-Lead LLP (Note 2)
35
˚C/W
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, TJ, the junction-to-ambient thermal resistance, θJA, and the
ambient temperature, TA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown.
The value of θJA (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.
The effective value of θJA can be reduced by using a heatsink (see Application Hints for specific information on heatsinking). The value of θJA for the LLP package
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 TA = TJ = 25˚C only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type).
All limits at TA = TJ = 25˚C are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control
methods.
Note 5: All limits are guaranteed at TA = TJ = 25˚C only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type).
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.
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LM2940/LM2940C
Electrical Characteristics
LM2940/LM2940C
Typical Performance Characteristics
Dropout Voltage
Dropout Voltage vs. Temperature
00882214
00882213
Output Voltage vs. Temperature
Quiescent Current vs. Temperature
00882215
00882216
Quiescent Current
Quiescent Current
00882217
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00882218
8
LM2940/LM2940C
Typical Performance Characteristics
(Continued)
Line Transient Response
Load Transient Response
00882220
00882219
Ripple Rejection
Low Voltage Behavior
00882225
00882221
Low Voltage Behavior
Low Voltage Behavior
00882227
00882226
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LM2940/LM2940C
Typical Performance Characteristics
(Continued)
Low Voltage Behavior
Low Voltage Behavior
00882228
00882229
Low Voltage Behavior
Output at Voltage Extremes
00882230
00882231
Output at Voltage Extremes
Output at Voltage Extremes
00882232
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00882233
10
LM2940/LM2940C
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
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LM2940/LM2940C
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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LM2940/LM2940C
Equivalent Schematic Diagram
00882201
Application Hints
Output Capacitor ESR
EXTERNAL CAPACITORS
The output capacitor is critical to maintaining regulator stability, and must meet the required conditions for both ESR
(Equivalent Series Resistance) and minimum amount of capacitance.
MINIMUM CAPACITANCE:
The minimum output capacitance required to maintain stability is 22 µF (this value may be increased without limit).
Larger values of output capacitance will give improved transient 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 essential 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 temperature operation.
Solid tantalum capacitors have a more stable ESR over
temperature, but are more expensive than aluminum electrolytics. A cost-effective approach sometimes used is to
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LM2940/LM2940C
Application Hints
HEATSINKING TO-220 PACKAGE PARTS
(Continued)
The TO-220 can be attached to a typical heatsink, or secured 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.
parallel an aluminum electrolytic with a solid Tantalum, with
the total capacitance split about 75/25% with the Aluminum
being the larger value.
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.
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 attachment, insulator, etc.). If the exact value is
unknown, 2˚C/W should be assumed for
θ(C−H).
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 junction temperature must be within the range specified under
Absolute Maximum Ratings.
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:
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.
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.
00882237
IIN = IL ÷ IG
PD = (VIN − VOUT) IL + (VIN) IG
FIGURE 2. Power Dissipation Diagram
The next parameter which must be calculated is the maximum allowable temperature rise, TR (max). This is calculated by using the formula:
TR (max) = TJ(max) − TA (max)
where: TJ (max) is the maximum allowable junction temperature, 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 maximum 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 package, no heatsink is needed since the package alone will
dissipate enough heat to satisfy these requirements.
If the calculated value for θ(JA)falls below these limits, a
heatsink is required.
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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.
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).
14
LM2940/LM2940C
Application Hints
(Continued)
00882240
FIGURE 5. θ(JA) vs. Copper (2 ounce) Area for the
SOT-223 Package
00882239
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
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LM2940/LM2940C
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
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16
LM2940/LM2940C
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
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LM2940/LM2940C
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
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18
LM2940/LM2940C 1A Low Dropout Regulator
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.
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Support Center
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2. A critical component is any component of a life
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can be reasonably expected to cause the failure of
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Tel: 81-3-5639-7560
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.