LM79MXX Series
3-Terminal Negative Regulators
General Description
The LM79MXX series of 3-terminal regulators is available
with fixed output voltages of −5V, −12V, and −15V. These
devices need only one external component—a compensa-
tion capacitor at the output. The LM79MXX series is pack-
aged in the TO-220 power package, and is capable of sup-
plying 0.5A 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 LM79MXX series allows out-
put voltage to be easily boosted above the preset value with
a resistor divider. The low quiescent current of these devices
with a specified maximum change with line and load ensures
good regulation in the voltage boosted mode.
For output voltage other than −5V, −12V, and −15V the
LM137 series provides an output voltage range from −1.2V
to −57V.
Features
nThermal, short circuit and safe area protection
nHigh ripple rejection
n0.5A output current
n4% tolerance on preset output voltage
Connection Diagram
TO-220 Plastic Package (T)
DS010483-7
Front View
Order Number LM79M05CT, LM79M12CT or LM79M15CT
See NS Package Number T03B
September 2001
LM79MXX Series 3-Terminal Negative Regulators
© 2001 National Semiconductor Corporation DS010483 www.national.com
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
= −5V −25V
V
O
= −12V, −15V −35V
Input/Output Differential
V
O
= −5V
V
O
= −12V, −15V 25V
30V
Power Dissipation (Note 2) Internally Limited
Operating Junction
Temperature Range 0˚C to +125˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature
(Soldering, 10 sec.) 230˚C
ESD Susceptibility TBD
Electrical Characteristics LM79M05C
Conditions unless otherwise noted: I
OUT
= 350mA, C
IN
= 2.2µF, C
OUT
= 1µF, 0˚C ≤T
J
≤+125˚C
Part Number LM79M05C
Output Voltage −5V Units
Input Voltage (Unless Otherwise Specified) −10V
Symbol Parameter Conditions Min Typ Max
V
O
Output Voltage T
J
= 25˚C −4.8 −5.0 −5.2 V
5mA ≤I
OUT
≤350mA −4.75 −5.25 V
(−25 ≤V
IN
≤−7)
∆V
O
Line Regulation T
J
= 25˚C (Note 3) 8 50 mV
(−25 ≤V
IN
≤−7)
230mV
(−18 ≤V
IN
≤−8)
∆V
O
Load Regulation T
J
= 25˚C, (Note 3) 30 100 mV
5mA ≤I
OUT
≤0.5A
I
Q
Quiescent Current T
J
= 25˚C 1 2 mA
∆I
Q
Quiescent Current With Input Voltage 0.4 mA
Change (−25 ≤V
IN
≤−8)
With Load,
5mA ≤I
OUT
≤350mA 0.4 mA
V
n
Output Noise Voltage T
A
= 25˚C, 150 µV
10Hz ≤f≤100Hz
Ripple Rejection f = 120Hz 54 66 dB
(−18 ≤V
IN
≤−8)
Dropout Voltage T
J
= 25˚C, I
OUT
= 0.5A 1.1 V
I
OMAX
Peak Output Current T
J
= 25˚C 800 mA
Average Temperature I
OUT
= 5mA,
Coefficient of 0˚C ≤T
J
≤100˚C −0.4 mV/˚C
Output Voltage
LM79MXX Series
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Electrical Characteristics LM79M12C, LM79M15C
Conditions unless otherwise noted: I
OUT
= 350mA, C
IN
= 2.2µF, C
OUT
= 1 µF, 0˚C ≤T
J
≤+125˚C
Part Number LM79M12C LM79M15C
Output Voltage −12V −15V Units
Input Voltage (Unless Otherwise Specified) −19V −23V
Symbol Parameter Conditions Min Typ Max Min Typ Max
V
O
Output Voltage T
J
= 25˚C −11.5 −12.0 −12.5 −14.4 −15.0 −15.6 V
5mA≤I
OUT
≤350mA −11.4 −12.6 −14.25 −15.75 V
(−27 ≤V
IN
≤−14.5) (−30 ≤V
IN
≤−10.5)
∆V
O
Line Regulation T
J
= 25˚C (Note 3) 5 80 5 80 mV
(−30 ≤V
IN
≤−14.5) (−30 ≤V
IN
≤−17.5)
3 50 3 50 mV
(−25 ≤V
IN
≤− 15) (−28 ≤V
IN
≤−18)
∆V
O
Load Regulation T
J
= 25˚C, (Note 3) 30 240 30 240 mV
5mA ≤I
OUT
≤0.5A
I
Q
Quiescent Current T
J
= 25˚C 1.5 3 1.5 3 mA
∆I
Q
Quiescent Current With Input Voltage 0.4 0.4 mA
Change (−30 ≤V
IN
≤−14.5) (−30 ≤V
IN
≤−27)
With Load,
5mA ≤I
OUT
≤350mA 0.4 0.4 mA
V
n
Output Noise T
A
= 25˚C, 400 400 µV
Voltage 10Hz ≤f≤100Hz
Ripple Rejection f = 120Hz 54 70 54 70 dB
(−25 ≤V
IN
≤−15) (−30 ≤V
IN
≤−17.5)
Dropout Voltage T
J
= 25˚C, I
OUT
= 0.5A 1.1 1.1 V
I
OMAX
Peak Output
Current T
J
= 25˚C 800 800 mA
Average Temperature I
OUT
= 5mA,
Coefficient of 0˚C ≤T
J
≤100˚C −0.8 −1.0 mV/˚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 measued 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 Performance Characteristics
Output Voltage vs. Temperature
DS010483-11
Ripple Rejection
DS010483-12
LM79MXX Series
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Typical Performance Characteristics (Continued)
Output Impedance
DS010483-13
Minimum Input-Output
Differential
DS010483-14
Quiescent Current vs. Input Voltage
DS010483-15
Quiescent Current vs. Load Current
DS010483-16
Short-Circuit Current
DS010483-17
Maximum Average Power
Dissipation (TO-220)
DS010483-18
LM79MXX Series
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Schematic Diagrams
−5V
DS010483-8
−12V and −15V
DS010483-9
LM79MXX Series
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Design Considerations
The LM79MXX fixed voltage regulator series have
thermal-overload protection from excessive power, internal
short-circuit protection which limits the circuit’s maximum
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 specified
temperature in order to meet data sheet specifications. To
calculate the maximum junction temperature or heat sink
required, the following thermal resistance values should be
used:
Package θ
JC
θ
JA
(˚C/W) (˚C/W)
TO-220 3 40
(1)
θ
CA
=θ
CS
+θ
SA
Solving for T
J
:
T
J
=T
A
+P
D
(θ
JC
+θ
CA
)or
=T
A
=+ P
D
θ
JA
(Without a Heat Sink)
Where
T
J
= Junction Temperature
T
A
= Ambient Temperature
P
D
= Power Dissipation
θ
JC
= Junction-to-Case Thermal Resistance
θ
CA
= Case-to-Ambient Thermal Resistance
θ
CS
= Case-to-Heat Sink Thermal Resistance
θ
SA
= Heat Sink-to-Ambient Thermal Resistance
θ
JA
= Junction-to-Ambient Thermal Resistance
Typical Applications
Bypass capacitors are necessary for stable operation of the
LM79MXX series of regulators over the input voltage and
output current ranges. Output bypass capacitors will improve
the transient response of the regulator.
The bypass capacitors (2.2µF on the input, 1.0µF on the
output), should be ceramic or solid tantalum which have
good high frequency characteristics. If aluminum electrolyt-
ics are used, their values should be 10µF or larger. The
bypass capacitors should be mounted with the shortest
leads, and if possible, directly across the regulator terminals.
Fixed Regulator
DS010483-2
*Required if regulator is separated from filter capacitor by more than 3".
For value given, capacitor must be solid tantalum. 25µF aluminum
electrolytic may be substituted.
†Required for stability. For value given, capacitor must be solid tantalum.
25µF aluminum electrolytic may be substituted. Values given may be
increased without limit.
For output capacitance in excess of 100µF, a high current diode from input
to output (1N4001, etc.) will protect the regulator from momentary input
shorts.
Variable Output
DS010483-3
*Improves transient response and ripple rejection.
Do not increase beyond 50µF.
Select R2 as follows:
LM79M05C 300Ω
LM79M12C 750Ω
LM79M15C 1k
LM79MXX Series
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Typical Applications (Continued)
Performance (Typical)
(−15) (+15)
Load Regulation at 0.5A 40mV 2 mV
Output Ripple, C
IN
= 3000µF, I
L
= 0.5A 100 µVrms 100 µVrms
Temperature Stability 50mV 50mV
Output Noise 10Hz ≤f≤10kHz 150 µVrms 150 µVrms
±15V, 1 Amp Tracking Regulators
DS010483-1
*Resistor tolerance of R4 and R5 determine matching of (+) and (−) outputs.
**Necessary only if raw supply filter capacitors are more than 3" from regulators.
Dual Trimmed Supply
DS010483-4
LM79MXX Series
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Physical Dimensions inches (millimeters) unless otherwise noted
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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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www.national.com
TO-220 Plastic Package (T)
Order Number LM79M05CT, LM79M12CT or LM79M15CT
NS Package Number T03B
LM79MXX Series 3-Terminal Negative Regulators
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.
