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
nDropout voltage typically 0.5V @I
O
=1A
nOutput current in excess of 1A
nOutput voltage trimmed before assembly
nReverse battery protection
nInternal short circuit current limit
nMirror image insertion protection
nP
+
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
Output Voltage Package
5.0 8.0 9.0 10 12 15
0˚C TJ125˚C LM2940CT-5.0 LM2940CT-9.0 LM2940CT-12 LM2940CT-15 TO-220
LM2940CS-5.0 LM2940CS-9.0 LM2940CS-12 LM2940CS-15 TO-263
−40˚C TJ
125˚C
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
−40˚C TJ
125˚C
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
−40˚C TJ
85˚C
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
−55˚C T
J
125˚C 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
www.national.com 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
www.national.com3
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 150˚C
Storage Temperature Range −65˚C T
J
+150˚C
Lead Temperature, Time for Wave Soldering
TO-220 (T) Package 260˚C, 10s
TO-263 (S) Package 260˚C, 4s
SOT-223 (MP) Package 260˚C, 4s
ESD Susceptibility (Note 3) 2 kV
Operating Conditions (Note 1)
Input Voltage 26V
Temperature Range
LM2940T, LM2940S −40˚C T
J
125˚C
LM2940CT, LM2940CS 0˚C T
J
125˚C
LM2940IMP −40˚C T
J
85˚C
LM2940J, LM2940WG −55˚C T
J
125˚C
LM2940LD −40˚C T
J
125˚C
Electrical Characteristics
V
IN
=V
O
+ 5V, I
O
= 1A, C
O
= 22 µF, 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
= 25˚C.
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
+2VV
IN
26V, 20 50 40/50 20 80 50/80 mV
MAX
I
O
=5mA
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
=5mA
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 µV
rms
Voltage I
O
=5mA
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
=5mA
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
www.national.com 4
Electrical Characteristics (Continued)
V
IN
=V
O
+ 5V, I
O
= 1A, C
O
= 22 µF, 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
= 25˚C.
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 1ms 5545 5545
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 µF, 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
= 25˚C.
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
+2VV
IN
26V, 20 90 20 100 mV
MAX
I
O
=5mA
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
=5mA
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 µV
rms
Voltage I
O
=5mA
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
www.national.com5
Electrical Characteristics (Continued)
V
IN
=V
O
+ 5V, I
O
= 1A, C
O
= 22 µF, 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
= 25˚C.
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 µF, 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
= 25˚C.
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
+2VV
IN
26V, 20 120 75/120 20 150 95/150 mV
MAX
I
O
=5mA
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
=5mA
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 µV
rms
Voltage I
O
=5mA
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
=5mA
LM2940/LM2940C
www.national.com 6
Electrical Characteristics (Continued)
V
IN
=V
O
+ 5V, I
O
= 1A, C
O
= 22 µF, 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
= 25˚C.
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 1ms5545 5545
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, 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 k.
Note 4: All limits are guaranteed at TA=T
J= 25˚C only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type).
All limits at TA=T
J= 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=T
J= 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.
LM2940/LM2940C
www.national.com7
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
www.national.com 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
www.national.com9
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
www.national.com 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
www.national.com11
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
www.national.com 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 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.
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
Output Capacitor ESR
00882206
FIGURE 1. ESR Limits
LM2940/LM2940C
www.national.com13
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 125˚C 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, θ
(JA)
, can now be found:
θ
(JA)
=T
R
(max)/P
D
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.
If the calculated value for θ
(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 θ
(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, 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 at-
tachment, insulator, etc.). If the exact value is
unknown, 2˚C/W should be assumed for
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.
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.
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).
00882237
IIN =I
L÷I
G
PD=(V
IN −V
OUT)I
L+(V
IN)I
G
FIGURE 2. Power Dissipation Diagram
00882238
FIGURE 3. θ
(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 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.
00882239
FIGURE 4. Maximum Power Dissipation vs. T
AMB
for
the TO-263 Package
00882240
FIGURE 5. θ
(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.com15
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.com17
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
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Fax: 65-6250 4466
Email: ap.support@nsc.com
Tel: 65-6254 4466
National Semiconductor
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.