LM79XX.PDF

November 1994

LM79XX Series 3-Terminal Negative Regulators

General Description

The LM79XX series of 3-terminal regulators is available with

fixed output voltages of b 5V, b 8V, b 12V, and b 15V.

These devices need only one external componentÐa com-

pensation capacitor at the output. The LM79XX series is

packaged in the TO-220 power package and is capable of

supplying 1.5A of output current.

These regulators employ internal current limiting safe area

protection and thermal shutdown for protection against vir-

tually all overload conditions.

Low ground pin current of the LM79XX series allows output

voltage to be easily boosted above the preset value with a

resistor divider. The low quiescent current drain of

these devices with a specified maximum change with line

and load ensures good regulation in the voltage boosted

mode.

For applications requiring other voltages, see LM137 data

sheet.

Features

Y Thermal, short circuit and safe area protection

Y High ripple rejection

Y 1.5A output current

Y 4% tolerance on preset output voltage

Connection Diagrams

TO-220 Package

Typical Applications

Fixed Regulator

TL/H/7340±14

TL/H/7340±3

*Required if regulator is separated from filter capacitor by

more than 3 × . For value given, capacitor must be solid

tantalum. 25 m F aluminum electrolytic may be substituted.

² Required for stability. For value given, capacitor must be

solid tantalum. 25 m F aluminum electrolytic may be substi-

tuted. Values given may be increased without limit.

For output capacitance in excess of 100 m F, a high current

diode from input to output (1N4001, etc.) will protect the

regulator from momentary input shorts.

Front View

Order Number LM7905CT, LM7912CT or LM7915CT

See NS Package Number TO3B

C 1995 National Semiconductor Corporation

TL/H/7340

RRD-B30M115/Printed in U. S. A.

Input-Output Differential

(V o eb 5V) 25V

(V o eb 12V and b 15V) 30V

Power Dissipation (Note 2) Internally Limited

Operating Junction Temperature Range 0 § Cto a 125 § C

Storage Temperature Range b 65 § Cto a 150 § C

Lead Temperature (Soldering, 10 sec.) 230 § C

Electrical Characteristics Conditions unless otherwise noted: I OUT e 500 mA, C IN e 2.2 m F, C OUT e 1 m F,

0 § C s T J s a 125 § C, Power Dissipation s 1.5W.

Part Number

b 25V

(V o eb 12V and b 15V)

b 35V

LM7905C

Output Voltage

b 5V

Units

Input Voltage (unless otherwise specified)

b 10V

Symbol

Parameter

Conditions

Min

Typ

Max

V O

Output Voltage

T J e 25 § C

b 4.8 b 5.0 b 5.2

5mA s I OUT s 1A,

b 4.75

b 5.25

P s 15W

( b 20 s V IN s b 7)

D V O

Line Regulation

T J e 25 § C, (Note 3)

( b 25 s V IN s b 7)

( b 12 s V IN s b 8)

D V O

Load Regulation

T J e 25 § C, (Note 3)

5mA s I OUT s 1.5A

100

250 mA s I OUT s 750 mA

I Q

Quiescent Current

T J e 25 § C

D I Q

Quiescent Current With Line

0.5

Change

( b 25 s V IN s b 7)

With Load, 5 mA s I OUT s 1A

0.5

V n

Output Noise Voltage T A e 25 § C, 10 Hz s f s 100 Hz

125

m V

Ripple Rejection

f e 120 Hz

( b 18 s V IN s b 8)

Dropout Voltage

T J e 25 § C, I OUT e 1A

1.1

I OMAX

Peak Output Current

T J e 25 § C

2.2

Average Temperature I OUT e 5 mA,

0.4

mV/ § C

Coefficient of

0 C s T J s 100 § C

Output Voltage

Typical Applications (Continued)

Variable Output

*Improves transient response and ripple rejection. Do not increase beyond 50 m F.

TL/H/7340±2

V OUT e V SET

R1 a R2

Select R2 as follows:

LM7905CT 300 X

LM7912CT 750 X

LM7915CT 1k

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Input Voltage

(V o eb 5V)

Electrical Characteristics (Continued) Conditions unless otherwise noted: I OUT e 500 mA, C IN e 2.2 m F,

C OUT e 1 m F, 0 § C s T J s a 125 § C, Power Dissipation e 1.5W.

Part Number

LM7912C

LM7915C

Output Voltage

b 12V

b 15V

Units

Input Voltage (unless otherwise specified)

b 19V

b 23V

Symbol

Parameter

Conditions

Min Typ Max Min Typ Max

V O Output Voltage

T J e 25 § C

b 11.5 b 12.0 b 12.5 b 14.4 b 15.0 b 15.6 V

5mA s I OUT s 1A,

b 11.4

b 12.6 b 14.25

b 15.75 V

P s 15W

( b 27 s V IN s b 14.5)

( b 30 s V IN s b 17.5)

D V O Line Regulation

T J e 25 § C, (Note 3)

100 mV

( b 30 s V IN s b 14.5)

( b 30 s V IN s b 17.5)

50 mV

( b 22 s V IN s b 16)

( b 26 s V IN s b 20)

D V O Load Regulation

T J e 25 § C, (Note 3)

5mA s I OUT s 1.5A

15 200

200 mV

250 mA s I OUT s 750 mA

75 mV

I Q Quiescent Current T J e 25 § C

1.5

3 mA

D I Q Quiescent Current With Line

0.5

0.5 mA

Change

( b 30 s V IN s b 14.5)

( b 30 s V IN s b 17.5)

With Load, 5 mA s I OUT s 1A

0.5

0.5 mA

V n Output Noise Voltage T A e 25 § C, 10 Hz s f s 100 Hz

300

375

m V

Ripple Rejection

f e 120 Hz

( b 25 s V IN s b 15)

( b 30 s V IN s b 17.5)

Dropout Voltage

T J e 25 § C, I OUT e 1A

1.1

I OMAX Peak Output Current T J e 25 § C

2.2

Average Temperature I OUT e 5 mA,

b 0.8

b 1.0

mV/ § C

Coefficient of

0 C s T J s 100 § C

Output Voltage

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

intended to be functional, but do not guarantee Specific Performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: Refer to Typical Performance Characteristics and Design Considerations for details.

Note 3: Regulation is measured at a constant junction temperature by pulse testing with a low duty cycle. Changes in output voltage due to heating effects must be

taken into account.

Typical Applications (Continued)

Dual Trimmed Supply

TL/H/7340±4

Design Considerations

The LM79XX fixed voltage regulator series has thermal

overload protection from excessive power dissipation, inter-

nal short circuit protection which limits the circuit's maxi-

mum current, and output transistor safe-area compensation

for reducing the output current as the voltage across the

pass transistor is increased.

Although the internal power dissipation is limited, the junc-

tion temperature must be kept below the maximum speci-

fied temperature (125 § C) in order to meet data sheet specifi-

cations. To calculate the maximum junction temperature or

heat sink required, the following thermal resistance values

should be used:

Where:

T J e Junction Temperature

T A e Ambient Temperature

P D e Power Dissipation

i JA e Junction-to-Ambient Thermal Resistance

i JC e Junction-to-Case Thermal Resistance

i CA e Case-to-Ambient Thermal Resistance

i CS e Case-to-Heat Sink Thermal Resistance

i SA e Heat Sink-to-Ambient Thermal Resistance

Typical Applications (Continued)

Bypass capacitors are necessary for stable operation of the

LM79XX series of regulators over the input voltage and out-

put current ranges. Output bypass capacitors will improve

the transient response by the regulator.

The bypass capacitors, (2.2 m F on the input, 1.0 m Fonthe

output) should be ceramic or solid tantalum which have

good high frequency characteristics. If aluminum electrolyt-

ics are used, their values should be 10 m F or larger. The

bypass capacitors should be mounted with the shortest

leads, and if possible, directly across the regulator termi-

nals.

Typ Max

Package

i JC i JC i JA i JA

§ C/W § C/W § C/W § C/W

TO-220

3.0

5.0

or T J Max T A

i JA

i CA e i CS a i SA (without heat sink)

Solving for T J :

T J e T A a P D ( i JC a i CA )or

e T A a P D i JA (without heat sink)

P D MAX e T J Max b T A

i JC a i CA

High Stability 1 Amp Regulator

TL/H/7340±5

Load and line regulation k 0.01% temperature stability s 0.2%

Determine Zener current

Solid tantalum

*Select resistors to set output voltage. 2 ppm/ § C tracking suggested

²²

Typical Applications (Continued)

Current Source

*I OUT e 1mA a

TL/H/7340±7

Light Controller Using Silicon Photo Cell

TL/H/7340±8

*Lamp brightness increase until i I e i Q ( & 1 mA) a 5V/R1.

Necessary only if raw supply filter capacitor is more than 2 × from LM7905CT

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