LM340/LM78XX Series
3-Terminal Positive Regulators
General Description
The LM140/LM340A/LM340/LM78XXC monolithic
3-terminal positive voltage regulators employ internal
current-limiting, thermal shutdown and safe-area compensa-
tion, making them essentially indestructible. If adequate heat
sinking is provided, they can deliver over 1.0A output cur-
rent. They are intended as fixed voltage regulators in a wide
range of applications including local (on-card) regulation for
elimination of noise and distribution problems associated
with single-point regulation. In addition to use as fixed volt-
age regulators, these devices can be used with external
components to obtain adjustable output voltages and cur-
rents.
Considerable effort was expended to make the entire series
of regulators easy to use and minimize the number of exter-
nal components. It is not necessary to bypass the output,
although this does improve transient response. Input by-
passing is needed only if the regulator is located far from the
filter capacitor of the power supply.
The 5V, 12V, and 15V regulator options are available in the
steel TO-3 power package. The LM340A/LM340/LM78XXC
series is available in the TO-220 plastic power package, and
the LM340-5.0 is available in the SOT-223 package, as well
as the LM340-5.0 and LM340-12 in the surface-mount TO-
263 package.
Features
nComplete specifications at 1A load
nOutput voltage tolerances of ±2% at T
j
= 25˚C and ±4%
over the temperature range (LM340A)
nLine regulation of 0.01% of V
OUT
/V of ∆V
IN
at 1A load
(LM340A)
nLoad regulation of 0.3% of V
OUT
/A (LM340A)
nInternal thermal overload protection
nInternal short-circuit current limit
nOutput transistor safe area protection
nP
+
Product Enhancement tested
Typical Applications
Fixed Output Regulator Adjustable Output Regulator
00778101
*Required if the regulator is located far from the power supply filter.
**Although no output capacitor is needed for stability, it does help transient
response. (If needed, use 0.1 µF, ceramic disc).
00778102
VOUT = 5V + (5V/R1 + IQ) R2 5V/R1 >3I
Q,
load regulation (Lr)≈[(R1 + R2)/R1] (Lrof LM340-5).
Current Regulator
Comparison between SOT-223 and D-Pak (TO-252)
Packages
00778103
∆IQ= 1.3 mA over line and load changes.
00778138
Scale 1:1
July 2006
LM340/LM78XX Series 3-Terminal Positive Regulators
© 2006 National Semiconductor Corporation DS007781 www.national.com
Ordering Information
Package Temperature
Range
Part Number Packaging Marking Transport Media NSC
Drawing
3-Lead TO-3 -55˚C to +125˚C LM140K-5.0 LM140K 5.0P+ 50 Per Tray K02A
LM140K-12 LM140K 12P+ 50 Per Tray
LM140K-15 LM140K 15P+ 50 Per Tray
0˚C to +125˚C LM340K-5.0 LM340K 5.0 7805P+ 50 Per Tray
LM340K-12 LM340K 12 7812P+ 50 Per Tray
LM340K-15 LM340K 15 7815P+ 50 Per Tray
3-lead TO-220 0˚C to +125˚C LM340AT-5.0 LM340AT 5.0 P+ 45 Units/Rail T03B
LM340T-5.0 LM340T5 7805 P+ 45 Units/Rail
LM340T-12 LM340T12 7812 P+ 45 Units/Rail
LM340T-15 LM340T15 7815 P+ 45 Units/Rail
LM7808CT LM7808CT 45 Units/Rail
3-Lead TO-263 0˚C to +125˚C LM340S-5.0 LM340S-5.0 P+ 45 Units/Rail TS3B
LM340SX-5.0 500 Units Tape and Reel
LM340S-12 LM340S-12 P+ 45 Units/Rail
LM340SX-12 500 Units Tape and Reel
LM340AS-5.0 LM340AS-5.0 P+ 45 Units/Rail
LM340ASX-5.0 500 Units Tape and Reel
4-Lead
SOT-223
0˚C to +125˚C LM340MP-5.0 N00A 1k Units Tape and Reel MP04A
LM340MPX-5.0 2k Units Tape and Reel
Unpackaged
Die
−55˚C to 125˚C LM140KG-5 MD8 Waffle Pack or Gel Pack DL069089
LM140KG-12 MD8 Waffle Pack or Gel Pack DL059093
LM140KG-15 MD8 Waffle Pack or Gel Pack DL059093
0˚C to +125˚C LM340-5.0 MDA Waffle Pack or Gel Pack DI074056
LM7808C MDC Waffle Pack or Gel Pack DI074056
Connection Diagrams
TO-3 Metal Can Package (K) TO-220 Power Package (T)
00778111
Bottom View
See Package Number K02A
00778112
Top View
See Package Number T03B
TO-263 Surface-Mount Package (S) 3-Lead SOT-223
00778120
Top View
See Package Number TS3B
00778143
Top View
See Package Number MP04A
LM340/LM78XX
www.national.com 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
(Note 5)
DC Input Voltage 35V
Internal Power Dissipation (Note 2) Internally Limited
Maximum Junction Temperature 150˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature (Soldering, 10 sec.)
TO-3 Package (K) 300˚C
TO-220 Package (T), TO-263
Package (S) 230˚C
ESD Susceptibility (Note 3) 2 kV
Operating Conditions (Note 1)
Temperature Range (T
A
) (Note 2)
LM140 −55˚C to +125˚C
LM340A, LM340 0˚C to +125˚C
LM7808C 0˚C to +125˚C
LM340A Electrical Characteristics
I
OUT
= 1A, 0˚C ≤T
J
≤+ 125˚C (LM340A) unless otherwise specified (Note 4)
Output Voltage 5V 12V 15V
Symbol Input Voltage (unless otherwise noted) 10V 19V 23V Units
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max
V
O
Output Voltage T
J
= 25˚C 4.9 5 5.1 11.75 12 12.25 14.7 15 15.3 V
P
D
≤15W, 5 mA ≤I
O
≤1A 4.8 5.2 11.5 12.5 14.4 15.6 V
V
MIN
≤V
IN
≤V
MAX
(7.5 ≤V
IN
≤20) (14.8 ≤V
IN
≤27) (17.9 ≤V
IN
≤30) V
∆V
O
Line Regulation I
O
= 500 mA 10 18 22 mV
∆V
IN
(7.5 ≤V
IN
≤20) (14.8 ≤V
IN
≤27) (17.9 ≤V
IN
≤30) V
T
J
= 25˚C 3 10 4 18 4 22 mV
∆V
IN
(7.5 ≤V
IN
≤20) (14.5 ≤V
IN
≤27) (17.5 ≤V
IN
≤30) V
T
J
= 25˚C 4 9 10 mV
Over Temperature 12 30 30 mV
∆V
IN
(8 ≤V
IN
≤12) (16 ≤V
IN
≤22) (20 ≤V
IN
≤26) V
∆V
O
Load Regulation T
J
= 25˚C 5 mA ≤I
O
≤1.5A 10 25 12 32 12 35 mV
250 mA ≤I
O
≤750
mA
15 19 21 mV
Over Temperature, 25 60 75 mV
5mA≤I
O
≤1A
I
Q
Quiescent
Current
T
J
= 25˚C 6 6 6 mA
Over Temperature 6.5 6.5 6.5 mA
∆I
Q
Quiescent
Current
5mA≤I
O
≤1A 0.5 0.5 0.5 mA
Change T
J
= 25˚C, I
O
= 1A 0.8 0.8 0.8 mA
V
MIN
≤V
IN
≤V
MAX
(7.5 ≤V
IN
≤20) (14.8 ≤V
IN
≤27) (17.9 ≤V
IN
≤30) V
I
O
= 500 mA 0.8 0.8 0.8 mA
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤25) (15 ≤V
IN
≤30) (17.9 ≤V
IN
≤30) V
V
N
Output Noise
Voltage
T
A
= 25˚C, 10 Hz ≤f≤100 kHz 40 75 90 µV
Ripple Rejection T
J
= 25˚C, f = 120 Hz, I
O
=1A688061726070dB
or f = 120 Hz, I
O
= 500 mA, 68 61 60 dB
Over Temperature,
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤18) (15 ≤V
IN
≤25) (18.5 ≤V
IN
≤
28.5)
V
R
O
Dropout Voltage T
J
= 25˚C, I
O
= 1A 2.0 2.0 2.0 V
Output
Resistance
f=1kHz 8 18 19 mΩ
Short-Circuit
Current
T
J
= 25˚C 2.1 1.5 1.2 A
LM340/LM78XX
www.national.com3
LM340A Electrical Characteristics (Continued)
I
OUT
= 1A, 0˚C ≤T
J
≤+ 125˚C (LM340A) unless otherwise specified (Note 4)
Output Voltage 5V 12V 15V
Symbol Input Voltage (unless otherwise noted) 10V 19V 23V Units
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max
Peak Output
Current
T
J
= 25˚C 2.4 2.4 2.4 A
Average TC of
V
O
Min, T
J
= 0˚C, I
O
= 5 mA −0.6 −1.5 −1.8 mV/˚C
V
IN
Input Voltage T
J
= 25˚C
Required to
Maintain
7.5 14.5 17.5 V
Line Regulation
LM140 Electrical Characteristics (Note 4)
−55˚C ≤T
J
≤+150˚C unless otherwise specified
Output Voltage 5V 12V 15V
Symbol Input Voltage (unless otherwise noted) 10V 19V 23V Units
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max
V
O
Output Voltage T
J
= 25˚C, 5 mA ≤I
O
≤1A 4.8 5 5.2 11.5 12 12.5 14.4 15 15.6 V
P
D
≤15W, 5 mA ≤I
O
≤1A 4.75 5.25 11.4 12.614.25 15.75 V
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤20) (15.5 ≤V
IN
≤27) (18.5 ≤V
IN
≤
30)
V
∆V
O
Line Regulation I
O
= 500 mA T
J
= 25˚C 3 50 4 120 4 150 mV
∆V
IN
(7 ≤V
IN
≤25) (14.5 ≤V
IN
≤30) (17.5 ≤V
IN
≤
30)
V
−55˚C ≤T
J
≤+150˚C 50 120 150 mV
∆V
IN
(8 ≤V
IN
≤20) (15 ≤V
IN
≤27) (18.5 ≤V
IN
≤
30)
V
I
O
≤1A T
J
= 25˚C 50 120 150 mV
∆V
IN
(7.5 ≤V
IN
≤20) (14.6 ≤V
IN
≤27) (17.7 ≤V
IN
≤
30)
V
−55˚C ≤T
J
≤+150˚C 25 60 75 mV
∆V
IN
(8 ≤V
IN
≤12) (16 ≤V
IN
≤22) (20 ≤V
IN
≤26) V
∆V
O
Load Regulation T
J
= 25˚C 5 mA ≤I
O
≤1.5A 10 50 12 120 12 150 mV
250 mA ≤I
P
≤750
mA
25 60 75 mV
−55˚C ≤T
J
≤+150˚C, 50 120 150 mV
5mA≤I
O
≤1A
I
Q
Quiescent Current I
O
≤1A T
J
= 25˚C 6 6 6 mA
−55˚C ≤T
J
≤+150˚C 7 7 7 mA
∆I
Q
Quiescent Current 5 mA ≤I
O
≤1A 0.5 0.5 0.5 mA
Change T
J
= 25˚C, I
O
≤1A 0.8 0.8 0.8 mA
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤20) (15 ≤V
IN
≤27) (18.5 ≤V
IN
≤
30)
V
I
O
= 500 mA, −55˚C ≤T
J
≤+150˚C 0.8 0.8 0.8 mA
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤25) (15 ≤V
IN
≤30) (18.5 ≤V
IN
≤
30)
V
V
N
Output Noise
Voltage
T
A
= 25˚C, 10 Hz ≤f≤100 kHz 40 75 90 µV
LM340/LM78XX
www.national.com 4
LM140 Electrical Characteristics (Note 4) (Continued)
−55˚C ≤T
J
≤+150˚C unless otherwise specified
Output Voltage 5V 12V 15V
Symbol Input Voltage (unless otherwise noted) 10V 19V 23V Units
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max
Ripple Rejection I
O
≤1A, T
J
= 25˚C
or
68 80 61 72 60 70 dB
f = 120 Hz I
O
≤500 mA, 68 61 60 dB
−55˚C ≤T
J
≤+150˚C
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤18) (15 ≤V
IN
≤25) (18.5 ≤V
IN
≤
28.5)
V
R
O
Dropout Voltage T
J
= 25˚C, I
O
= 1A 2.0 2.0 2.0 V
Output Resistance f=1kHz 8 18 19 mΩ
Short-Circuit
Current
T
J
= 25˚C 2.1 1.5 1.2 A
Peak Output
Current
T
J
= 25˚C 2.4 2.4 2.4 A
Average TC of
V
OUT
0˚C ≤T
J
≤+150˚C, I
O
= 5 mA −0.6 −1.5 −1.8 mV/˚C
V
IN
Input Voltage T
J
= 25˚C, I
O
≤1A
Required to
Maintain
7.5 14.6 17.7 V
Line Regulation
LM340 Electrical Characteristics (Note 4)
0˚C ≤T
J
≤+125˚C unless otherwise specified
Output Voltage 5V 12V 15V
Symbol Input Voltage (unless otherwise noted) 10V 19V 23V Units
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max
V
O
Output Voltage T
J
= 25˚C, 5 mA ≤I
O
≤1A 4.8 5 5.2 11.5 12 12.5 14.4 15 15.6 V
P
D
≤15W, 5 mA ≤I
O
≤1A 4.75 5.25 11.4 12.6 14.25 15.75 V
V
MIN
≤V
IN
≤V
MAX
(7.5 ≤V
IN
≤20) (14.5 ≤V
IN
≤
27)
(17.5 ≤V
IN
≤30) V
∆V
O
Line Regulation I
O
= 500 mA T
J
= 25˚C 3 50 4 120 4 150 mV
∆V
IN
(7 ≤V
IN
≤25) (14.5 ≤V
IN
≤
30)
(17.5 ≤V
IN
≤30) V
0˚C ≤T
J
≤+125˚C 50 120 150 mV
∆V
IN
(8 ≤V
IN
≤20) (15 ≤V
IN
≤27) (18.5 ≤V
IN
≤30) V
I
O
≤1A T
J
= 25˚C 50 120 150 mV
∆V
IN
(7.5 ≤V
IN
≤20) (14.6 ≤V
IN
≤
27)
(17.7 ≤V
IN
≤30) V
0˚C ≤T
J
≤+125˚C 25 60 75 mV
∆V
IN
(8 ≤V
IN
≤12) (16 ≤V
IN
≤22) (20 ≤V
IN
≤26) V
∆V
O
Load Regulation T
J
= 25˚C 5 mA ≤I
O
≤1.5A 10 50 12 120 12 150 mV
250 mA ≤I
O
≤750 mA 25 60 75 mV
5mA≤I
O
≤1A, 0˚C ≤T
J
≤
+125˚C
50 120 150 mV
I
Q
Quiescent Current I
O
≤1A T
J
= 25˚C 8 8 8 mA
0˚C ≤T
J
≤+125˚C 8.5 8.5 8.5 mA
∆I
Q
Quiescent Current 5 mA ≤I
O
≤1A 0.5 0.5 0.5 mA
Change T
J
= 25˚C, I
O
≤1A 1.0 1.0 1.0 mA
LM340/LM78XX
www.national.com5
LM340 Electrical Characteristics (Note 4) (Continued)
0˚C ≤T
J
≤+125˚C unless otherwise specified
Output Voltage 5V 12V 15V
Symbol Input Voltage (unless otherwise noted) 10V 19V 23V Units
Parameter Conditions Min Typ Max Min Typ Max Min Typ Max
V
MIN
≤V
IN
≤V
MAX
(7.5 ≤V
IN
≤20) (14.8 ≤V
IN
≤
27)
(17.9 ≤V
IN
≤30) V
I
O
≤500 mA, 0˚C ≤T
J
≤+125˚C 1.0 1.0 1.0 mA
V
MIN
≤V
IN
≤V
MAX
(7 ≤V
IN
≤25) (14.5 ≤V
IN
≤
30)
(17.5 ≤V
IN
≤30) V
V
N
Output Noise
Voltage
T
A
= 25˚C, 10 Hz ≤f≤100 kHz 40 75 90 µV
Ripple Rejection I
O
≤1A, T
J
=
25˚C
62 80 55 72 54 70 dB
f = 120 Hz or I
O
≤500 mA, 62 55 54 dB
0˚C ≤T
J
≤+125˚C
V
MIN
≤V
IN
≤V
MAX
(8 ≤V
IN
≤18) (15 ≤V
IN
≤25) (18.5 ≤V
IN
≤
28.5)
V
R
O
Dropout Voltage T
J
= 25˚C, I
O
= 1A 2.0 2.0 2.0 V
Output Resistance f=1kHz 8 18 19 mΩ
Short-Circuit Current T
J
= 25˚C 2.1 1.5 1.2 A
Peak Output
Current
T
J
= 25˚C 2.4 2.4 2.4 A
Average TC of V
OUT
0˚C ≤T
J
≤+125˚C, I
O
= 5 mA −0.6 −1.5 −1.8 mV/˚C
V
IN
Input Voltage T
J
= 25˚C, I
O
≤1A
Required to
Maintain
7.5 14.6 17.7 V
Line Regulation
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 at any ambient temperature is a function of the maximum junction temperature for operation (TJMAX = 125˚C or
150˚C), the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA). PDMAX =(T
JMAX −T
A)/θJA. If this dissipation is exceeded, the die
temperature will rise above TJMAX and the electrical specifications do not apply. If the die temperature rises above 150˚C, the device will go into thermal shutdown.
For the TO-3 package (K, KC), the junction-to-ambient thermal resistance (θJA) is 39˚C/W. When using a heatsink, θJA is the sum of the 4˚C/W junction-to-case
thermal resistance (θJC) of the TO-3 package and the case-to-ambient thermal resistance of the heatsink. For the TO-220 package (T), θJA is 54˚C/W and θJC is
4˚C/W. If SOT-223 is used, the junction-to-ambient thermal resistance is 174˚C/W and can be reduced by a heatsink (see Applications Hints on heatsinking).
If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package: Using 0.5 square
inches of copper area, θJA is 50˚C/W; with 1 square inch of copper area, θJAis 37˚C/W; and with 1.6 or more inches of copper area, θJA is 32˚C/W.
Note 3: ESD rating is based on the human body model, 100 pF discharged through 1.5 kΩ.
Note 4: All characteristics are measured with a 0.22 µF capacitor from input to ground and a 0.1 µF capacitor from output to ground. All characteristics except noise
voltage and ripple rejection ratio are measured using pulse techniques (tw≤10 ms, duty cycle ≤5%). Output voltage changes due to changes in internal temperature
must be taken into account separately.
Note 5: Military datasheets are available upon request. At the time of printing, the military datasheet specifications for the LM140K-5.0/883, LM140K-12/883, and
LM140K-15/883 complied with the min and max limits for the respective versions of the LM140. The LM140H and LM140K may also be procured as JAN devices
on slash sheet JM38510/107.
LM340/LM78XX
www.national.com 6
LM7808C
Electrical Characteristics
0˚C ≤T
J
≤+150˚C, V
I
= 14V, I
O
= 500 mA, C
I
= 0.33 µF, C
O
= 0.1 µF, unless otherwise specified
Symbol Parameter Conditions (Note 6) LM7808C Units
Min Typ Max
V
O
Output Voltage T
J
= 25˚C 7.7 8.0 8.3 V
∆V
O
Line Regulation T
J
= 25˚C 10.5V ≤V
I
≤25V 6.0 160 mV
11.0V ≤V
I
≤17V 2.0 80
∆V
O
Load Regulation T
J
= 25˚C 5.0 mA ≤I
O
≤1.5A 12 160 mV
250 mA ≤I
O
≤750
mA
4.0 80
V
O
Output Voltage 11.5V ≤V
I
≤23V, 5.0 mA ≤I
O
≤1.0A, P ≤15W 7.6 8.4 V
I
Q
Quiescent Current T
J
= 25˚C 4.3 8.0 mA
∆I
Q
Quiescent With Line 11.5V ≤V
I
≤25V 1.0 mA
Current Change With Load 5.0 mA ≤I
O
≤1.0A 0.5
V
N
Noise T
A
= 25˚C, 10 Hz ≤f≤100 kHz 52 µV
∆V
I
/∆V
O
Ripple Rejection f = 120 Hz, I
O
= 350 mA, T
J
= 25˚C 56 72 dB
V
DO
Dropout Voltage I
O
= 1.0A, T
J
= 25˚C 2.0 V
R
O
Output Resistance f = 1.0 kHz 16 mΩ
I
OS
Output Short Circuit Current T
J
= 25˚C, V
I
= 35V 0.45 A
I
PK
Peak Output Current T
J
= 25˚C 2.2 A
∆V
O
/∆T Average Temperature I
O
= 5.0 mA 0.8 mV/˚C
Coefficient of Output Voltage
Note 6: All characteristics are measured with a 0.22 µF capacitor from input to ground and a 0.1 µF capacitor from output to ground. All characteristics except noise
voltage and ripple rejection ratio are measured using pulse techniques (tw≤10 ms, duty cycle ≤5%). Output voltage changes due to changes in internal temperature
must be taken into account separately.
LM340/LM78XX
www.national.com7
Typical Performance Characteristics
Maximum Average Power Dissipation Maximum Average Power Dissipation
00778122 00778123
Maximum Power Dissipation (TO-263)
(See Note 2) Output Voltage (Normalized to 1V at T
J
= 25˚C)
00778124 00778125
Note: Shaded area refers to LM340A/LM340, LM7805C, LM7812C and
LM7815C.
Ripple Rejection Ripple Rejection
00778126 00778127
LM340/LM78XX
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Typical Performance Characteristics (Continued)
Output Impedance Dropout Characteristics
00778128 00778129
Quiescent Current Peak Output Current
00778130
Note: Shaded area refers to LM340A/LM340, LM7805C, LM7812C and
LM7815C.
00778131
Dropout Voltage Quiescent Current
00778132
Note: Shaded area refers to LM340A/LM340, LM7805C, LM7812C and
LM7815C. 00778133
LM340/LM78XX
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Line Regulation
140AK-5.0, I
OUT
= 1A, T
A
= 25˚C
Line Regulation
140AK-5.0, V
IN
= 10V, T
A
= 25˚C
00778105 00778106
Equivalent Schematic
00778107
LM340/LM78XX
www.national.com 10
Application Hints
The LM340/LM78XX series is designed with thermal protec-
tion, output short-circuit protection and output transistor safe
area protection. However, as with any IC regulator, it be-
comes necessary to take precautions to assure that the
regulator is not inadvertently damaged. The following de-
scribes possible misapplications and methods to prevent
damage to the regulator.
SHORTING THE REGULATOR INPUT
When using large capacitors at the output of these regula-
tors, a protection diode connected input to output (Figure 1)
may be required if the input is shorted to ground. Without the
protection diode, an input short will cause the input to rapidly
approach ground potential, while the output remains near
the initial V
OUT
because of the stored charge in the large
output capacitor. The capacitor will then discharge through a
large internal input to output diode and parasitic transistors.
If the energy released by the capacitor is large enough, this
diode, low current metal and the regulator will be destroyed.
The fast diode in Figure 1 will shunt most of the capacitors
discharge current around the regulator. Generally no protec-
tion diode is required for values of output capacitance ≤10
µF.
RAISING THE OUTPUT VOLTAGE ABOVE THE INPUT
VOLTAGE
Since the output of the device does not sink current, forcing
the output high can cause damage to internal low current
paths in a manner similar to that just described in the “Short-
ing the Regulator Input” section.
REGULATOR FLOATING GROUND (Figure 2)
When the ground pin alone becomes disconnected, the
output approaches the unregulated input, causing possible
damage to other circuits connected to V
OUT
. If ground is
reconnected with power “ON”, damage may also occur to the
regulator. This fault is most likely to occur when plugging in
regulators or modules with on card regulators into powered
up sockets. Power should be turned off first, thermal limit
ceases operating, or ground should be connected first if
power must be left on.
TRANSIENT VOLTAGES
If transients exceed the maximum rated input voltage of the
device, or reach more than 0.8V below ground and have
sufficient energy, they will damage the regulator. The solu-
tion is to use a large input capacitor, a series input break-
down diode, a choke, a transient suppressor or a combina-
tion of these.
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 this catalog, or shown in a curve that plots temperature
rise vs power dissipation for the heatsink.
00778108
FIGURE 1. Input Short
00778109
FIGURE 2. Regulator Floating Ground
00778110
FIGURE 3. Transients
LM340/LM78XX
www.national.com11
Application Hints (Continued)
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 plane.
shows for the TO-263 the measured values of θ
(J–A)
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
(J–A)
for the TO-263
package mounted to a PCB is 32˚C/W.
As a design aid, Figure 5 shows the maximum allowable
power dissipation compared to ambient temperature for the
TO-263 device (assuming θ
(J–A)
is 35˚C/W and the maxi-
mum junction temperature is 125˚C).
Figures 6, 7 show the information for the SOT-223 package.
Figure 6 assumes a θ
(J–A)
of 74˚C/W for 1 ounce copper and
51˚C/W for 2 ounce copper and a maximum junction tem-
perature of 125˚C.
Please see AN-1028 for power enhancement techniques to
be used with the SOT-223 package.
00778139
FIGURE 4. θ
(J–A)
vs Copper (1 ounce)
Area for the TO-263 Package
00778140
FIGURE 5. Maximum Power Dissipation vs
T
AMB
for the TO-263 Package
00778141
FIGURE 6. θ
(J–A)
vs Copper (2 ounce) Area
for the SOT-223 Package
00778142
FIGURE 7. Maximum Power Dissipation vs
T
AMB
for the SOT-223 Package
LM340/LM78XX
www.national.com 12
Typical Applications
Fixed Output Regulator
00778113
Note: Bypass capacitors are recommended for optimum stability and transient response, and should be located as close as possible to the regulator.
High Input Voltage Circuits
00778114
00778115
High Current Voltage Regulator
00778116
LM340/LM78XX
www.national.com13
Typical Applications (Continued)
High Output Current, Short Circuit Protected
00778117
Positive and Negative Regulator
00778118
LM340/LM78XX
www.national.com 14
Physical Dimensions inches (millimeters) unless otherwise noted
TO-3 Metal Can Package (K)
NS Package Number K02A
TO-263 Surface-Mount Package (S)
NS Package Number TS3B
LM340/LM78XX
www.national.com15
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
TO-220 Power Package (T)
NS Package Number T03B
3-Lead SOT-223 Package
NS Package Number MP04A
LM340/LM78XX
www.national.com 16
Notes
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.
For the most current product information visit us at www.national.com.
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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.
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and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at:
www.national.com/quality/green.
Lead free products are RoHS compliant.
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LM340/LM78XX Series 3-Terminal Positive Regulators
