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LM138/LM338 5-Amp Adjustable Regulators
Check for Samples: LM138,LM338
A unique feature of the LM138 family is time-
1FEATURES dependent current limiting. The current limit circuitry
2• Specified 7A Peak Output Current allows peak currents of up to 12A to be drawn from
• Specified 5A Output Current the regulator for short periods of time. This allows the
LM138 to be used with heavy transient loads and
• Adjustable Output Down to 1.2V speeds start-up under full-load conditions. Under
• Specified Thermal Regulation sustained loading conditions, the current limit
• Current Limit Constant with Temperature decreases to a safe value protecting the regulator.
Also included on the chip are thermal overload
• P+Product Enhancement Tested protection and safe area protection for the power
• Output is Short-Circuit Protected transistor. Overload protection remains functional
even if the adjustment pin is accidentally
APPLICATIONS disconnected.
• Adjustable Power Supplies Normally, no capacitors are needed unless the device
• Constant Current Regulators is situated more than 6 inches from the input filter
capacitors in which case an input bypass is needed.
• Battery Chargers An output capacitor can be added to improve
transient response, while bypassing the adjustment
DESCRIPTION pin will increase the regulator's ripple rejection.
The LM138 series of adjustable 3-terminal positive
voltage regulators is capable of supplying in excess Besides replacing fixed regulators or discrete
of 5A over a 1.2V to 32V output range. They are designs, the LM138 is useful in a wide variety of
exceptionally easy to use and require only 2 resistors other applications. Since the regulator is “floating”
to set the output voltage. Careful circuit design has and sees only the input-to-output differential voltage,
resulted in outstanding load and line supplies of several hundred volts can be regulated as
regulation—comparable to many commercial power long as the maximum input to output differential is not
supplies. The LM138 family is supplied in a standard exceeded, i.e., do not short-circuit output to ground.
3-lead transistor package. The part numbers in the LM138 series which have a
K suffix are packaged in a standard Steel TO-3
package, while those with a T suffix are packaged in
a TO-220 plastic package. The LM138 is rated for
−55°C ≤TJ≤+150°C, and the LM338 is rated for 0°C
≤TJ≤+125°C.
Connection Diagram
Connection Diagrams
Figure 1. (TO-3) Metal Can Package Figure 2. (TO-220) Plastic Package
Bottom View Front View
See Package Number NDS0002A See Package Number NDE0003B
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 1998–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
LM138, LM338
SNVS771B –MAY 1998–REVISED APRIL 2013
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings(1)(2)(3)
Power Dissipation Internally limited
Input/Output Voltage Differential +40V, −0.3V
Storage Temperature −65°C to +150°C
Lead Temperature
TO-3 Package (Soldering, 10 seconds) 300°C
TO-220 Package (Soldering, 4 seconds) 260°C
ESD Tolerance TBD
(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 ensure specific performance limits. For ensured specifications and test
conditions, see the Electrical Characteristics.
(2) Refer to RETS138K drawing for military specifications of LM138K.
(3) If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
Operating Temperature Range
LM138 −55°C ≤TJ≤+150°C
LM338 0°C ≤TJ≤+125°C
Electrical Characteristics
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating
Temperature Range. Unless otherwise specified, VIN −VOUT = 5V; and IOUT = 10 mA. (1)
LM138
Symbol Parameter Conditions Units
Min Typ Max
VREF Reference Voltage 3V ≤(VIN −VOUT)≤35V, 1.19 1.24 1.29 V
10 mA ≤IOUT ≤5A, P ≤50W
VRLINE Line Regulation 3V ≤(VIN −VOUT)≤35V (2) 0.005 0.01 %/V
0.02 0.04 %/V
VRLOAD Load Regulation 10 mA ≤IOUT ≤5A (2) 0.1 0.3 %
0.3 0.6 %
Thermal Regulation 20 ms Pulse 0.002 0.01 %/W
IADJ Adjustment Pin Current 45 100 μA
ΔIADJ Adjustment Pin Current Change 10 mA ≤IOUT ≤5A, 0.2 5 μA
3V ≤(VIN −VOUT)≤35V
ΔVR/T Temperature Stability TMIN ≤TJ≤TMAX 1%
ILOAD(Min) Minimum Load Current VIN −VOUT = 35V 3.5 5 mA
ICL Current Limit VIN −VOUT ≤10V
DC 5 8 A
0.5 ms Peak 7 12 A
VIN −VOUT = 30V 1 1 A
VNRMS Output Noise, % of VOUT 10 Hz ≤f≤10 kHz 0.003 %
ΔVR/ΔVIN Ripple Rejection Ratio VOUT = 10V, f = 120 Hz, CADJ = 0 μF60 dB
VOUT = 10V, f = 120 Hz, CADJ = 10 μF60 75 dB
Long-Term Stability TJ= 125°C, 1000 Hrs 0.3 1 %
θJC Thermal Resistance, NDS Package 1 °C/W
Junction to Case
(1) These specifications are applicable for power dissipations up to 50W for the TO-3 (NDS) package and 25W for the TO-220 (NDE)
package. Power dissipation is specified at these values up to 15V input-output differential. Above 15V differential, power dissipation will
be limited by internal protection circuitry. All limits (i.e., the numbers in the Min. and Max. columns) are specified to TI's AOQL (Average
Outgoing Quality Level).
(2) Regulation is measured at a constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to
heating effects are covered under the specifications for thermal regulation.
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Electrical Characteristics (continued)
Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating
Temperature Range. Unless otherwise specified, VIN −VOUT = 5V; and IOUT = 10 mA. (1)
LM138
Symbol Parameter Conditions Units
Min Typ Max
θJA Thermal Resistance, Junction to NDS Package 35 °C/W
Ambient (No Heat Sink)
Electrical Characteristics LM338
Symbol Parameter Conditions Units
Min Typ Max
VREF Reference Voltage 3V ≤(VIN −VOUT)≤35V, 1.19 1.24 1.29 V
10 mA ≤IOUT ≤5A, P ≤50W
VRLINE Line Regulation 3V ≤(VIN −VOUT)≤35V (1) 0.005 0.03 %/V
0.02 0.06 %/V
VRLOAD Load Regulation 10 mA ≤IOUT ≤5A (1) 0.1 0.5 %
0.3 1 %
Thermal Regulation 20 ms Pulse 0.002 0.02 %/W
IADJ Adjustment Pin Current 45 100 μA
ΔIADJ Adjustment Pin Current Change 10 mA ≤IOUT ≤5A, 0.2 5 μA
3V ≤(VIN −VOUT)≤35V
ΔVR/T Temperature Stability TMIN ≤TJ≤TMAX 1%
ILOAD(Min) Minimum Load Current VIN −VOUT = 35V 3.5 10 mA
ICL Current Limit VIN −VOUT ≤10V
DC 5 8 A
0.5 ms Peak 7 12 A
VIN −VOUT = 30V 1 A
VNRMS Output Noise, % of VOUT 10 Hz ≤f≤10 kHz 0.003 %
ΔVR/ΔVIN Ripple Rejection Ratio VOUT = 10V, f = 120 Hz, CADJ = 0 μF60 dB
VOUT = 10V, f = 120 Hz, CADJ = 10 μF60 75 dB
Long-Term Stability TJ= 125°C, 1000 hrs 0.3 1 %
θJC Thermal Resistance NDS Package 1 °C/W
Junction to Case NDE Package 4 °C/W
θJA Thermal Resistance, Junction to NDS Package 35 °C/W
Ambient (No Heat Sink) NDE Package 50 °C/W
(1) Regulation is measured at a constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to
heating effects are covered under the specifications for thermal regulation.
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Typical Performance Characteristics
Current Limit Current Limit
Figure 3. Figure 4.
Current Limit Load Regulation
Figure 5. Figure 6.
Adjustment
Dropout Voltage Current
Figure . Figure 7.
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Typical Performance Characteristics (continued)
Temperature Stability Output Impedance
Figure 8. Figure 9.
Minimum Operating
Current Ripple Rejection
Figure 10. Figure 11.
Ripple Rejection Ripple Rejection
Figure 12. Figure 13.
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APPLICATION HINTS
In operation, the LM138 develops a nominal 1.25V reference voltage, VREF, between the output and adjustment
terminal. The reference voltage is impressed across program resistor R1 and, since the voltage is constant, a
constant current I1then flows through the output set resistor R2, giving an output voltage of
(1)
Since the 50 μA current from the adjustment terminal represents an error term, the LM138 was designed to
minimize IADJ and make it very constant with line and load changes. To do this, all quiescent operating current is
returned to the output establishing a minimum load current requirement. If there is insufficient load on the output,
the output will rise.
EXTERNAL CAPACITORS
An input bypass capacitor is recommended. A 0.1 μF disc or 1 μF solid tantalum on the input is suitable input
bypassing for almost all applications. The device is more sensitive to the absence of input bypassiing when
adjustment or output capacitors are used but the above values will eliminate the possiblity of problems.
The adjustment terminal can be bypassed to ground on the LM138 to improve ripple rejection. This bypass
capacitor prevents ripple from being amplified as the output voltage is increased. With a 10 μF bypass capacitor
75 dB ripple rejection is obtainable at any output level. Increases over 20 μF do not appreciably improve the
ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to
include protection diodes to prevent the capacitor from discharging through internal low current paths and
damaging the device.
In general, the best type of capacitors to use are solid tantalum. Solid tantalum capacitors have low impedance
even at high frequencies. Depending upon capacitor construction, it takes about 25 μF in aluminum electrolytic to
equal 1 μF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some
types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 μF disc may
seem to work better than a 0.1 μF disc as a bypass.
Although the LM138 is stable with no output capacitors, like any feedback circuit, certain values of external
capacitance can cause excessive ringing. This occurs with values between 500 pF and 5000 pF. A 1 μF solid
tantalum (or 25 μF aluminum electrolytic) on the output swamps this effect and insures stability.
LOAD REGULATION
The LM138 is capable of providing extremely good load regulation but a few precautions are needed to obtain
maximum performance. The current set resistor connected between the adjustment terminal and the output
terminal (usually 240Ω) should be tied directly to the output of the regulator (case) rather than near the load. This
eliminates line drops from appearing effectively in series with the reference and degrading regulation. For
example, a 15V regulator with 0.05Ωresistance between the regulator and load will have a load regulation due to
line resistance of 0.05Ω× IL. If the set resistor is connected near the load the effective line resistance will be
0.05Ω(1 + R2/R1) or in this case, 11.5 times worse.
Figure 16 shows the effect of resistance between the regulator and 240Ωset resistor.
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Figure 16. Regulator with Line Resistance in Output Lead
With the TO-3 package, it is easy to minimize the resistance from the case to the set resistor, by using 2
separate leads to the case. The ground of R2 can be returned near the ground of the load to provide remote
ground sensing and improve load regulation.
PROTECTION DIODES
When external capacitors are used with any IC regulator it is sometimes necessary to add protection diodes to
prevent the capacitors from discharging through low current points into the regulator. Most 20 μF capacitors have
low enough internal series resistance to deliver 20A spikes when shorted. Although the surge is short, there is
enough energy to damage parts of the IC.
When an output capacitor is connected to a regulator and the input is shorted, the output capacitor will discharge
into the output of the regulator. The discharge current depends on the value of the capacitor, the output voltage
of the regulator, and the rate of decrease of VIN. In the LM138 this discharge path is through a large junction that
is able to sustain 25A surge with no problem. This is not true of other types of positive regulators. For output
capacitors of 100 μF or less at output of 15V or less, there is no need to use diodes.
The bypass capacitor on the adjustment terminal can discharge through a low current junction. Discharge occurs
when either the input or output is shorted. Internal to the LM138 is a 50Ωresistor which limits the peak discharge
current. No protection is needed for output voltages of 25V or less and 10 μF capacitance. Figure 17 shows an
LM138 with protection diodes included for use with outputs greater than 25V and high values of output
capacitance.
D1 protects against C1
D2 protects against C2
Figure 17. Regulator with Protection Diodes
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Typical Applications
Regulator and Voltage Reference 1.2V–25V Adjustable Regulator
Temperature Controller
Full output current not available at high input-output voltages
†Optional—improves transient response. Output capacitors in the range of 1 μF to 1000 μF of aluminum or tantalum electrolytic are
commonly used to provide improved output impedance and rejection of transients.
*Needed if device is more than 6 inches from filter capacitors.
**R1 = 240Ωfor LM138. R1, R2 as an assembly can be ordered from Bourns:
MIL part no. 7105A-AT2-502
COMM part no. 7105A-AT7-502
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Schematic Diagram
Typical Applications Precision Power Regulator with Low Temperature Coefficient
* Adjust for 3.75 across R1
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Slow Turn-On 15V Regulator Adjustable Regulator with Improved Ripple Rejection
†Solid tantalum
*Discharges C1 if output is shorted to ground
**R1 = 240Ωfor LM138
High Stability 10V Regulator Digitally Selected Outputs
*Sets maximum VOUT
**R1 = 240Ωfor LM138
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0 to 22V Regulator
* R1 = 240Ω, R2 = 5k for LM138
Full output current not available at high input-output voltages
12V Battery Charger
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Adjustable Current Regulator Precision Current Limiter
5A Current Regulator Tracking Preregulator
Adjusting Multiple On-Card Regulators with Single Control*
† Minimum load—10 mA
* All outputs within ±100 mV
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Power Amplifier
AV= 1, RF= 10k, CF= 100 pF
AV= 10, RF= 100k, CF= 10 pF
Bandwidth ≥100 kHz
Distortion ≤0.1%
Simple 12V Battery Charger
Use of RSallows low charging rates with fully charged battery.
**The 1000 μF is recommended to filter out input transients
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Adjustable 15A Regulator
Current Limited 6V Charger
* Set max charge current to 3A
** THE 1000 μF is recommended to filter out input transients.
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REVISION HISTORY
Changes from Revision A (April 2013) to Revision B Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 17
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PACKAGE OPTION ADDENDUM
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Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LM138K STEEL ACTIVE TO-3 NDS 2 50 TBD Call TI Call TI -55 to 125 LM138K
STEELP+
LM138K STEEL/NOPB ACTIVE TO-3 NDS 2 50 Green (RoHS
& no Sb/Br) POST-PLATE Level-1-NA-UNLIM -55 to 125 LM138K
STEELP+
LM338K STEEL ACTIVE TO-3 NDS 2 50 TBD Call TI Call TI 0 to 125 LM338K
STEELP+
LM338K STEEL/NOPB ACTIVE TO-3 NDS 2 50 Green (RoHS
& no Sb/Br) POST-PLATE Level-1-NA-UNLIM 0 to 125 LM338K
STEELP+
LM338T NRND TO-220 NDE 3 45 TBD Call TI Call TI 0 to 125 LM338T P+
LM338T/NOPB ACTIVE TO-220 NDE 3 45 Green (RoHS
& no Sb/Br) CU SN Level-1-NA-UNLIM 0 to 125 LM338T P+
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
PACKAGE OPTION ADDENDUM
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Addendum-Page 2
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
MECHANICAL DATA
NDS0002A
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