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 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 (V
IN
- V
OUT
3V).
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
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.
Features
n
Dropout voltage typically 0.5V
@
I
O
= 1A
n
Output current in excess of 1A
n
Output voltage trimmed before assembly
n
Reverse battery protection
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
OUT
must be at least 22 F 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
Output Voltage
Package
5.0
8.0
9.0
10
12
15
0C
T
J
125C LM2940CT-5.0
LM2940CT-9.0
LM2940CT-12
LM2940CT-15
TO-220
LM2940CS-5.0
LM2940CS-9.0
LM2940CS-12
LM2940CS-15
TO-263
-40C
T
J
125C
LM2940LD-5.0
LM2940LD-8.0
LM2940LD-9.0
LM2940LD-10
LM2940LD-12
LM2940LD-15
LLP 1k
Units
Tape and
Reel
LM2940LDX-5.0
LM2940LDX-8.0
LM2940LDX-9.0
LM2940LDX-10
LM2940LDX-12
LM2940LDX-15
LLP 4.5k
Units
Tape and
Reel
-40C
T
J
125C
LM2940T-5.0
LM2940T-8.0
LM2940T-9.0
LM2940T-10
LM2940T-12
TO-220
LM2940S-5.0
LM2940S-8.0
LM2940S-9.0
LM2940S-10
LM2940S-12
TO-263
-40C
T
J
85C
LM2940IMP-5.0
LM2940IMP-8.0
LM2940IMP-9.0
LM2940IMP-10
LM2940IMP-12
LM2940IMP-15
SOT-223
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.
January 2003
LM2940/LM2940C
1A
Low
Dropout
Regulator
2003 National Semiconductor Corporation
DS008822
www.national.com
Ordering Information
(Continued)
Temperature
Range
Output Voltage
Package
5.0
8.0
12
15
-55C
T
J
125C
LM2940J-5.0/883
5962-8958701EA
LM2940J-8.0/883
5962-9088301QEA
LM2940J-12/883
5962-9088401QEA
LM2940J-15/883
5962-9088501QEA
J16A
LM2940WG5.0/883
5962-8958701XA
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
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
00882242
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 Dual-in-Line Package (J)
00882243
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
16-Lead Ceramic Surface-Mount Package (WG)
00882244
Top View
Order Number LM2940WG5.0/883 (5962-8958701XA)
See NS Package Number WG16A
LM2940/LM2940C
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2
Connection Diagrams
(Continued)
(TO-263) Surface-Mount Package
00882211
Top View
8-Lead LLP
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
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
LM2940/LM2940C
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3
Absolute Maximum Ratings
(Note 1)
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
Internal Power Dissipation
(Note 2)
Internally Limited
Maximum Junction Temperature
150C
Storage Temperature Range
-65C
T
J
+150C
Lead Temperature, Time for Wave Soldering
TO-220 (T) Package
260C, 10s
TO-263 (S) Package
260C, 4s
SOT-223 (MP) Package
260C, 4s
ESD Susceptibility (Note 3)
2 kV
Operating Conditions
(Note 1)
Input Voltage
26V
Temperature Range
LM2940T, LM2940S
-40C
T
J
125C
LM2940CT, LM2940CS
0C
T
J
125C
LM2940IMP
-40C
T
J
85C
LM2940J, LM2940WG
-55C
T
J
125C
LM2940LD
-40C
T
J
125C
Electrical Characteristics
V
IN
= V
O
+ 5V, I
O
= 1A, C
O
= 22 F, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for T
A
= T
J
= 25C.
Output Voltage (V
O
)
5V
8V
Units
LM2940
LM2940/883
LM2940
LM2940/883
Parameter
Conditions
Typ
Limit
Limit
Typ
Limit
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
6.25V
V
IN
26V
9.4V
V
IN
26V
Output Voltage
5 mA
I
O
1A
5.00
4.85/4.75
4.85/4.75
8.00
7.76/7.60
7.76/7.60
V
MIN
5.15/5.25
5.15/5.25
8.24/8.40
8.24/8.40
V
MAX
Line Regulation
V
O
+ 2V
V
IN
26V,
20
50
40/50
20
80
50/80
mV
MAX
I
O
= 5 mA
Load Regulation
50 mA
I
O
1A
LM2940, LM2940/883
35
50/80
50/100
55
80/130
80/130
mV
MAX
LM2940C
35
50
55
80
Output
100 mADC and
Impedance
20 mArms,
35
1000/1000
55
1000/1000
m
f
O
= 120 Hz
Quiescent
V
O
+2V
V
IN
26V,
Current
I
O
= 5 mA
LM2940, LM2940/883
10
15/20
15/20
10
15/20
15/20
mA
MAX
LM2940C
10
15
V
IN
= V
O
+ 5V,
30
45/60
50/60
30
45/60
50/60
mA
MAX
I
O
= 1A
Output Noise
10 Hz - 100 kHz,
150
700/700
240
1000/1000
V
rms
Voltage
I
O
= 5 mA
Ripple Rejection
f
O
= 120 Hz, 1 V
rms
,
I
O
= 100 mA
LM2940
72
60/54
66
54/48
dB
MIN
LM2940C
72
60
66
54
f
O
= 1 kHz, 1 V
rms
,
60/50
54/48
dB
MIN
I
O
= 5 mA
Long Term
20
32
mV/
Stability
1000 Hr
Dropout Voltage
I
O
= 1A
0.5
0.8/1.0
0.7/1.0
0.5
0.8/1.0
0.7/1.0
V
MAX
I
O
= 100 mA
110
150/200
150/200
110
150/200
150/200
mV
MAX
Short Circuit
Current
(Note 6)
1.9
1.6
1.5/1.3
1.9
1.6
1.6/1.3
A
MIN
LM2940/LM2940C
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4
Electrical Characteristics
(Continued)
V
IN
= V
O
+ 5V, I
O
= 1A, C
O
= 22 F, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for T
A
= T
J
= 25C.
Output Voltage (V
O
)
5V
8V
Units
LM2940
LM2940/883
LM2940
LM2940/883
Parameter
Conditions
Typ
Limit
Limit
Typ
Limit
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
Maximum Line
R
O
= 100
V
MIN
Transient
LM2940, T
100 ms
75
60/60
75
60/60
LM2940/883, T
20 ms
40/40
40/40
LM2940C, T
1 ms
55
45
55
45
Reverse Polarity
R
O
= 100
DC Input Voltage
LM2940, LM2940/883
-30
-15/-15
-15/-15
-30
-15/-15
-15/-15
V
MIN
LM2940C
-30
-15
-30
-15
Reverse Polarity
R
O
= 100
Transient Input
LM2940, T
100 ms
-75
-50/-50
-75
-50/-50
V
MIN
Voltage
LM2940/883, T
20 ms
-45/-45
-45/-45
LM2940C, T
1 ms
-55
-45/-45
Electrical Characteristics
V
IN
= V
O
+ 5V, I
O
= 1A, C
O
= 22 F, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for T
A
= T
J
= 25C.
Output Voltage (V
O
)
9V
10V
Units
Parameter
Conditions
Typ
LM2940
Typ
LM2940
Limit
Limit
(Note 4)
(Note 4)
10.5V
V
IN
26V
11.5V
V
IN
26V
Output Voltage
5 mA
I
O
1A
9.00
8.73/8.55
10.00
9.70/9.50
V
MIN
9.27/9.45
10.30/10.50
V
MAX
Line Regulation
V
O
+ 2V
V
IN
26V,
20
90
20
100
mV
MAX
I
O
= 5 mA
Load Regulation
50 mA
I
O
1A
LM2940
60
90/150
65
100/165
mV
MAX
LM2940C
60
90
Output Impedance
100 mADC and
20 mArms,
60
65
m
f
O
= 120 Hz
Quiescent
V
O
+2V
V
IN
<
26V,
Current
I
O
= 5 mA
LM2940
10
15/20
10
15/20
mA
MAX
LM2940C
10
15
V
IN
= V
O
+ 5V, I
O
= 1A
30
45/60
30
45/60
mA
MAX
Output Noise
10 Hz - 100 kHz,
270
300
V
rms
Voltage
I
O
= 5 mA
Ripple Rejection
f
O
= 120 Hz, 1 V
rms
,
I
O
= 100 mA
LM2940
64
52/46
63
51/45
dB
MIN
LM2940C
64
52
Long Term
Stability
34
36
mV/
1000 Hr
Dropout Voltage
I
O
= 1A
0.5
0.8/1.0
0.5
0.8/1.0
V
MAX
I
O
= 100 mA
110
150/200
110
150/200
mV
MAX
LM2940/LM2940C
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5
Electrical Characteristics
(Continued)
V
IN
= V
O
+ 5V, I
O
= 1A, C
O
= 22 F, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for T
A
= T
J
= 25C.
Output Voltage (V
O
)
9V
10V
Units
Parameter
Conditions
Typ
LM2940
Typ
LM2940
Limit
Limit
(Note 4)
(Note 4)
Short Circuit
(Note 6)
1.9
1.6
1.9
1.6
A
MIN
Current
Maximum Line
R
O
= 100
Transient
T
100 ms
LM2940
75
60/60
75
60/60
V
MIN
LM2940C
55
45
Reverse Polarity
R
O
= 100
DC Input Voltage
LM2940
-30
-15/-15
-30
-15/-15
V
MIN
LM2940C
-30
-15
Reverse Polarity
R
O
= 100
Transient Input
T
100 ms
Voltage
LM2940
-75
-50/-50
-75
-50/-50
V
MIN
LM2940C
-55
-45/-45
Electrical Characteristics
V
IN
= V
O
+ 5V, I
O
= 1A, C
O
= 22 F, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for T
A
= T
J
= 25C.
Output Voltage (V
O
)
12V
15V
Units
LM2940
LM2940/833
LM2940
LM2940/833
Parameter
Conditions
Typ
Limit
Limit
Typ
Limit
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
13.6V
V
IN
26V
16.75V
V
IN
26V
Output Voltage
5 mA
I
O
1A
12.00
11.64/11.40
11.64/11.40
15.00
14.55/14.25
14.55/14.25
V
MIN
12.36/12.60
12.36/12.60
15.45/15.75
15.45/15.75
V
MAX
Line Regulation
V
O
+ 2V
V
IN
26V,
20
120
75/120
20
150
95/150
mV
MAX
I
O
= 5 mA
Load Regulation
50 mA
I
O
1A
LM2940, LM2940/883
55
120/200
120/190
150/240
mV
MAX
LM2940C
55
120
70
150
Output
100 mADC and
Impedance
20 mArms,
80
1000/1000
100
1000/1000
m
f
O
= 120 Hz
Quiescent
Current
V
O
+2V
V
IN
26V,
I
O
= 5 mA
LM2940, LM2940/883
10
15/20
15/20
15/20
mA
MAX
LM2940C
10
15
10
15
V
IN
= V
O
+ 5V, I
O
= 1A
30
45/60
50/60
30
45/60
50/60
mA
MAX
Output Noise
10 Hz - 100 kHz,
360
1000/1000
450
1000/1000
V
rms
Voltage
I
O
= 5 mA
Ripple Rejection
f
O
= 120 Hz, 1 V
rms
,
I
O
= 100 mA
LM2940
66
54/48
dB
MIN
LM2940C
66
54
64
52
f
O
= 1 kHz, 1 V
rms
,
52/46
48/42
dB
MIN
I
O
= 5 mA
LM2940/LM2940C
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6
Electrical Characteristics
(Continued)
V
IN
= V
O
+ 5V, I
O
= 1A, C
O
= 22 F, unless otherwise specified. Boldface limits apply over the entire operating tempera-
ture range of the indicated device. All other specifications apply for T
A
= T
J
= 25C.
Output Voltage (V
O
)
12V
15V
Units
LM2940
LM2940/833
LM2940
LM2940/833
Parameter
Conditions
Typ
Limit
Limit
Typ
Limit
Limit
(Note 4)
(Note 5)
(Note 4)
(Note 5)
Long Term
48
60
mV/
Stability
1000 Hr
Dropout Voltage
I
O
= 1A
0.5
0.8/1.0
0.7/1.0
0.5
0.8/1.0
0.7/1.0
V
MAX
I
O
= 100 mA
110
150/200
150/200
110
150/200
150/200
mV
MAX
Short Circuit
(Note 6)
1.9
1.6
1.6/1.3
1.9
1.6
1.6/1.3
A
MIN
Current
Maximum Line
R
O
= 100
Transient
LM2940, T
100 ms
75
60/60
LM2940/883, T
20 ms
40/40
40/40
V
MIN
LM2940C, T
1 ms
55
45
55
45
Reverse Polarity
R
O
= 100
DC Input
LM2940, LM2940/883
-30
-15/-15
-15/-15
-15/-15
V
MIN
Voltage
LM2940C
-30
-15
-30
-15
Reverse Polarity
R
O
= 100
Transient Input
LM2940, T
100 ms
-75
-50/-50
Voltage
LM2940/883, T
20 ms
-45/-45
-45/-45
V
MIN
LM2940C, T
1 ms
-55
-45/-45
-55
-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, T
J
, the junction-to-ambient thermal resistance,
JA
, and the
ambient temperature, T
A
. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown.
The value of
JA
(for devices in still air with no heatsink) is 60C/W for the TO-220 package, 80C/W for the TO-263 package, and 174C/W for the SOT-223 package.
The effective value of
JA
can be reduced by using a heatsink (see Application Hints for specific information on heatsinking). The value of
JA
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 k
.
Note 4: All limits are guaranteed at T
A
= T
J
= 25C only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type).
All limits at T
A
= T
J
= 25C 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 T
A
= T
J
= 25C 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.
LM2940/LM2940C
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7
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
LM2940/LM2940C
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8
Typical Performance Characteristics
(Continued)
Line Transient Response
Load Transient Response
00882219
00882220
Ripple Rejection
Low Voltage Behavior
00882221
00882225
Low Voltage Behavior
Low Voltage Behavior
00882226
00882227
LM2940/LM2940C
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9
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
00882233
LM2940/LM2940C
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10
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
00882208
00882222
LM2940/LM2940C
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11
Typical Performance Characteristics
(Continued)
Maximum Power Dissipation (TO-220)
Maximum Power Dissipation (TO-3)
00882223
00882224
Maximum Power Dissipation (TO-263)
See (Note 2)
00882210
LM2940/LM2940C
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12
Equivalent Schematic Diagram
00882201
Application Hints
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 F (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.
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 25C to
-40C. 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
Output Capacitor ESR
00882206
FIGURE 1. ESR Limits
LM2940/LM2940C
www.national.com
13
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.
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.
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.
To determine if a heatsink is required, the power dissipated
by the regulator, P
D
, 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:
The next parameter which must be calculated is the maxi-
mum allowable temperature rise, T
R
(max). This is calcu-
lated by using the formula:
T
R
(max) = T
J
(max) - T
A
(max)
where: T
J
(max) is the maximum allowable junction tem-
perature, which is 125C for commercial
grade parts.
T
A
(max) is the maximum ambient temperature
which
will
be
encountered
in
the
application.
Using the calculated values for T
R
(max) and P
D
, the maxi-
mum allowable value for the junction-to-ambient thermal
resistance,
(JA)
, can now be found:
(JA)
= T
R
(max)/P
D
IMPORTANT: If the maximum allowable value for
(JA)
is
found to be
53C/W for the TO-220 package, 80C/W for
the TO-263 package, or
174C/W for the SOT-223 pack-
age, no heatsink is needed since the package alone will
dissipate enough heat to satisfy these requirements.
If the calculated value for
(JA)
falls below these limits, a
heatsink is required.
HEATSINKING TO-220 PACKAGE PARTS
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
(JA)
will be the same as shown in
the next section for the TO-263.
If a manufactured heatsink is to be selected, the value of
heatsink-to-ambient thermal resistance,
(H-A)
, must first be
calculated:
(H-A)
=
(JA)
-
(C-H)
-
(J-C)
Where:
(J-C)
is defined as the thermal resistance from the
junction to the surface of the case. A value of
3C/W can be assumed for
(J-C)
for this
calculation.
(C-H)
is defined as the thermal resistance between
the case and the surface of the heatsink. The
value of
(C-H)
will vary from about 1.5C/W to
about 2.5C/W (depending on method of at-
tachment, insulator, etc.). If the exact value is
unknown, 2C/W should be assumed for
(C-H)
.
When a value for
(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.
(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
(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.
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
(JA)
for the TO-263
package mounted to a PCB is 32C/W.
As a design aid, Figure 4 shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming
(JA)
is 35C/W and the maximum
junction temperature is 125C).
00882237
I
IN
= I
L
I
G
P
D
= (V
IN
- V
OUT
) I
L
+ (V
IN
) I
G
FIGURE 2. Power Dissipation Diagram
00882238
FIGURE 3.
(JA)
vs. Copper (1 ounce) Area for the
TO-263 Package
LM2940/LM2940C
www.national.com
14
Application Hints
(Continued)
Figure 5 and Figure 6 show the information for the SOT-223
package. Figure 6 assumes a
(JA)
of 74C/W for 1 ounce
copper and 51C/W for 2 ounce copper and a maximum
junction temperature of 125C.
00882239
FIGURE 4. Maximum Power Dissipation vs. T
AMB
for
the TO-263 Package
00882240
FIGURE 5.
(JA)
vs. Copper (2 ounce) Area for the
SOT-223 Package
00882241
FIGURE 6. Maximum Power Dissipation vs. T
AMB
for the SOT-223 Package
LM2940/LM2940C
www.national.com
15
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
LM2940/LM2940C
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
LM2940/LM2940C
www.national.com
17
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
LM2940/LM2940C
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
Americas Customer
Support Center
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
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Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
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Tel: 65-6254 4466
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Japan Customer Support Center
Fax: 81-3-5639-7507
Email: nsj.crc@jksmtp.nsc.com
Tel: 81-3-5639-7560
www.national.com
LM2940/LM2940C
1A
Low
Dropout
Regulator
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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