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LM138, LM338
SNVS771C – MAY 1998 – REVISED DECEMBER 2016
LM138 and LM338 5-Amp Adjustable Regulators
1 Features
3 Description
•
•
•
•
•
•
•
The LM138 series of adjustable 3-terminal positive
voltage regulators is capable of supplying in excess
of 5 A over a 1.2-V to 32-V output range. They are
exceptionally easy to use and require only 2 resistors
to set the output voltage. Careful circuit design has
resulted in outstanding load and line regulation,
comparable to many commercial power supplies. The
LM138 family is supplied in a standard 3-lead
transistor package.
Specified 7-A Peak Output Current
Specified 5-A Output Current
Adjustable Output Down to 1.2 V
Specified Thermal Regulation
Current Limit Constant With Temperature
P + Product Enhancement Tested
Output is Short-Circuit Protected
1
2 Applications
•
•
•
Adjustable Power Supplies
Constant Current Regulators
Battery Chargers
Available Packages
Pin 1. Adjustment
2. Output
3. Input
Tab/Case is Output
3
1
TO-220
TO-3
1
2
3
Typical Application Circuit
A unique feature of the LM138 family is timedependent current limiting. The current limit circuitry
allows peak currents of up to 12 A to be drawn from
the regulator for short periods of time. This allows the
LM138 to be used with heavy transient loads and
speeds start-up under full-load conditions. Under
sustained loading conditions, the current limit
decreases to a safe value protecting the regulator.
Also included on the chip are thermal overload
protection and safe area protection for the power
transistor. Overload protection remains functional
even if the adjustment (ADJ) pin is accidentally
disconnected.
Normally, no capacitors are needed unless the device
is situated more than 6 inches from the input filter
capacitors in which case an input bypass is needed.
An output capacitor can be added to improve
transient response, while bypassing the adjustment
pin increases the ripple rejection of the regulator.
Besides replacing fixed regulators or discrete
designs, the LM138 is useful in a wide variety of
other applications. Because the regulator is floating
and receives only the input-to-output differential
voltage, supplies of several hundred volts can be
regulated as long as the maximum input to output
differential is not exceeded; do not short-circuit output
to ground. The part numbers in the LM138 series
which have a K suffix are packaged in a standard
steel TO-CAN package, while those with a T suffix
are packaged in a TO-220 plastic package. The
LM138 is rated for TJ = –55°C to 150°C, and the
LM338 is rated for TJ = 0°C to 125°C.
Device Information(1)
PART NUMBER
LM138
Copyright © 2016, Texas Instruments Incorporated
LM338
PACKAGE
BODY SIZE (NOM)
TO-CAN (2)
25.40 mm × 38.94 mm
TO-220 (3)
10.16 mm × 14.986 mm
TO-CAN (2)
25.40 mm × 38.94 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM138, LM338
SNVS771C – MAY 1998 – REVISED DECEMBER 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
6.1
6.2
6.3
6.4
6.5
6.6
3
3
4
4
5
6
Absolute Maximum Ratings ......................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics: LM138..............................
Electrical Characteristics: LM338..............................
Typical Characteristics ..............................................
Detailed Description .............................................. 9
7.1
7.2
7.3
7.4
Overview ................................................................... 9
Functional Block Diagram ......................................... 9
Feature Description................................................... 9
Device Functional Modes........................................ 10
8
Application and Implementation ........................ 11
8.1 Application Information............................................ 11
8.2 Typical Applications ................................................ 12
8.3 System Examples ................................................... 17
9 Power Supply Recommendations...................... 23
10 Layout................................................................... 23
10.1 Layout Guidelines ................................................. 23
10.2 Layout Example .................................................... 23
11 Device and Documentation Support ................. 24
11.1
11.2
11.3
11.4
11.5
11.6
Receiving Notification of Documentation Updates
Related Links ........................................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
24
24
24
24
24
24
12 Mechanical, Packaging, and Orderable
Information ........................................................... 24
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision B (April 2013) to Revision C
Page
•
Added Device Information table, Pin Configuration and Functions section, Specifications section, Recommended
Operating Conditions table, Thermal Information table, Detailed Description section, Application and Implementation
section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and
Mechanical, Packaging, and Orderable Information section .................................................................................................. 1
•
Deleted RETS138K military specification reference from Absolute Maximum Ratings table................................................. 3
•
Changed Junction to Ambient, RθJA, value in Thermal Information table From: 50°C/W To: 22.9°C/W (NDE) ..................... 4
•
Changed Junction to Case, RθJC(top), value in Thermal Information table From: 4°C/W To: 15.7°C/W (NDE) ....................... 4
Changes from Revision A (April 2013) to Revision B
•
2
Page
Changed layout of National Semiconductor Data Sheet to TI format .................................................................................... 1
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5 Pin Configuration and Functions
NDS Package
2-Pin TO-CAN
Bottom View
NDE Package
3-Pin TO-220
Front View
Package Number NDE0003B
Package Number NDS0002A
Pin Functions
PIN
NAME
TO-220
TO-CAN
ADJ
1
1
VIN
3
VOUT
2
I/O
DESCRIPTION
I
Output voltage adjustment pin. Connect to a resistor divider to set VO
2
I
Supply input pin
Case
O
Voltage output pin
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
Input and output voltage differential
–0.3
40
V
Power dissipation
Internally limited
Lead temperature
Operating temperature, TJ
TO-3 package (soldering, 10 s)
300
TO-220 package (soldering, 4 s)
260
LM138
–55
150
LM338
0
125
–65
150
Storage temperature, Tstg
(1)
°C
°C
°C
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
6.2 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
Input-to-output voltage differential
Output current
MIN
MAX
3
40
UNIT
V
5
A
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6.3 Thermal Information
LM338
THERMAL METRIC (1)
LM338
NDS (TO-CAN)
NDE (TO-220)
NDS (TO-CAN)
2 PINS
3 PINS
2 PINS
35
22.9
35
°C/W
RθJC(top) Junction-to-case (top) thermal resistance
1
15.7
1
°C/W
RθJB
Junction-to-board thermal resistance
—
4.1
—
°C/W
ψJT
Junction-to-top characterization parameter
—
2.1
—
°C/W
ψJB
Junction-to-board characterization parameter
—
4.1
—
°C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance
—
0.7
—
°C/W
RθJA
(1)
Junction-to-ambient thermal resistance
UNIT
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report.
6.4 Electrical Characteristics: LM138
Values apply for TJ = 25°C; VIN – VOUT = 5 V; and IOUT = 10 mA (unless otherwise noted). (1)
PARAMETER
TEST CONDITIONS
VREF
Reference voltage
3 V ≤ (VIN – VOUT) ≤ 35 V, 10 mA ≤ IOUT ≤ 5 A, P ≤ 50 W,
TJ = –55°C to 150°C
VRLINE
Line regulation
3 V ≤ (VIN – VOUT) ≤ 35 V (2)
MIN
TYP
MAX
UNIT
1.19
1.24
1.29
V
0.005% 0.01%
V
0.02% 0.04%
V
TJ = 25°C
TJ = –55°C to 150°C
TJ = 25°C
0.1%
0.3%
0.3%
0.6%
Load regulation
10 mA ≤ IOUT ≤ 5 A (2)
Thermal regulation
20 ms pulse
IADJ
Adjustment pin current
TJ = –55°C to 150°C
45
100
µA
ΔIADJ
Adjustment pin current change
10 mA ≤ IOUT ≤ 5 A, 3 V ≤ (VIN – VOUT) ≤ 35 V,
TJ = –55°C to 150°C
0.2
5
µA
ΔVR/T
Temperature stability
TJ = –55°C to 150°C
1%
VIN – VOUT = 35 V, TJ = –55°C to 150°C
3.5
5
mA
VRLOAD
ILOAD(MIN) Minimum load current
TJ = –55°C to 150°C
0.002% 0.01%
W
VIN – VOUT ≤ 10 V
ICL
Current limit
VN
RMS output noise
(percent of VOUT)
ΔVR/ΔVIN Ripple rejection ratio
Long-term stability
(1)
(2)
4
DC, TJ = –55°C to 150°C
5
8
A
0.5-ms peak, TJ = –55°C to 150°C
7
12
A
VIN – VOUT = 30 V
1
10 Hz ≤ f ≤ 10 kHz
0.003%
VOUT = 10 V, f = 120 Hz, CADJ = 0 µF,
TJ = –55°C to 150°C
VOUT = 10 V, f = 120 Hz, CADJ = 10 µF,
TJ = –55°C to 150°C
TJ = 125°C, 1000 Hrs
60
1
A
60
dB
75
dB
0.3%
1%
These specifications are applicable for power dissipations up to 50 W for the TO-3 (NDS) package and 25 W for the TO-220 (NDE)
package. Power dissipation is specified at these values up to 15-V input-output differential. Above 15-V differential, power dissipation is
limited by internal protection circuitry. All limits (that is, the numbers in the minimum and maximum columns) are specified to TI's AOQL
(Average Outgoing Quality Level).
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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6.5 Electrical Characteristics: LM338
Values apply for TJ = 25°C; VIN – VOUT = 5 V; and IOUT = 10 mA (unless otherwise noted). (1)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1.19
1.24
1.29
V
0.005% 0.03%
V
0.02% 0.06%
V
VREF
Reference voltage
3 V ≤ (VIN – VOUT) ≤ 35 V, 10 mA ≤ IOUT ≤ 5 A, P ≤ 50 W,
TJ = 0°C to 125°C
VRLINE
Line regulation
3 V ≤ (VIN – VOUT) ≤ 35 V (2)
VRLOAD
Load regulation
10 mA ≤ IOUT ≤ 5 A (2)
Thermal regulation
20-ms pulse
Adjustment pin current
TJ = 0°C to 125°C
45
100
µA
ΔIADJ
Adjustment pin current change
10 mA ≤ IOUT ≤ 5 A, 3 V ≤ (VIN – VOUT) ≤ 35 V,
TJ = 0°C to 125°C
0.2
5
µA
ΔVR/T
Temperature stability
TJ = 0°C to 125°C
10
mA
IADJ
ILOAD(MIN) Minimum load current
TJ = 25°C
TJ = 0°C to 125°C
TJ = 25°C
0.1
0.5
TJ = 0°C to 125°C
0.3
1
0.002% 0.02%
W
1
VIN – VOUT = 35 V, TJ = 0°C to 125°C
3.5
VIN – VOUT ≤ 10 V
ICL
Current limit
DC, TJ = 0°C to 125°C
5
8
0.5-ms peak, TJ = 0°C to 125°C
7
12
VIN – VOUT = 30 V
VN
RMS output noise
(percent of VOUT)
ΔVR/ΔVIN Ripple rejection ratio
Long-term stability
(1)
(2)
A
0.003%
VOUT = 10 V, f = 120 Hz, CADJ = 0 µF,
TJ = 0°C to 125°C
TJ = 125°C, 1000 Hrs
A
1
10 Hz ≤ f ≤ 10 kHz
VOUT = 10 V, f = 120 Hz, CADJ = 10 µF,
TJ = 0°C to 125°C
A
60
60
dB
75
dB
0.3%
1%
These specifications are applicable for power dissipations up to 50 W for the TO-3 (NDS) package and 25 W for the TO-220 (NDE)
package. Power dissipation is specified at these values up to 15-V input-output differential. Above 15-V differential, power dissipation is
limited by internal protection circuitry. All limits (that is, the numbers in the minimum and maximum columns) are specified to TI's AOQL
(Average Outgoing Quality Level).
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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6.6 Typical Characteristics
Figure 1. Current Limit
Figure 2. Current Limit
Figure 4. Load Regulation
Figure 3. Current Limit
Figure 6. Adjustment Current
Figure 5. Dropout Voltage
6
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Typical Characteristics (continued)
Figure 7. Temperature Stability
Figure 8. Output Impedance
Figure 9. Minimum Operating Current
Figure 10. Ripple Rejection
Figure 11. Ripple Rejection
Figure 12. Ripple Rejection
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Typical Characteristics (continued)
Figure 13. Line Transient Response
8
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Figure 14. Load Transient Response
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7 Detailed Description
7.1 Overview
The LM138 and LM338 devices are adjustable, three-terminal, positive-voltage regulators capable of supplying
more than 5 A over an output-voltage range of 1.2 V to 32 V. It requires only two external resistors to set the
output voltage. These devices feature a typical line regulation of 0.005% and typical load regulation of 0.1%. It
includes time-dependent current limiting, thermal overload protection, and safe operating area protection.
Overload protection remains functional even if the ADJUST terminal is disconnected.
The LM138 and LM338 devices are versatile in their applications, including uses in programmable output
regulation and local on-card regulation. Or, by connecting a fixed resistor between the ADJUST and OUTPUT
terminals, the LM138 and LM338 devices can function as a precision current regulators. An optional output
capacitor can be added to improve transient response. The ADJUST terminal can be bypassed to achieve very
high ripple-rejection ratios, which are difficult to achieve with standard three-terminal regulators.
7.2 Functional Block Diagram
7.3 Feature Description
7.3.1 NPN Darlington Output Drive
NPN Darlington output topology provides naturally low output impedance and an output capacitor is optional. To
support maximum current and lowest temperature, 3-V headroom is recommended (VI – VO).
7.3.2 Overload Block
Overcurrent and overtemperature shutdown protects the device against overload or damage from operating in
excessive heat.
7.3.3 Programmable Feedback
Op amp with 1.25-V offset input at the ADJUST terminal provides easy output voltage or current (not both)
programming. For current regulation applications, a single resistor whose resistance value is 1.25 V/IO and
power rating is greater than 1.25 V2/R must be used. For voltage regulation applications, two resistors set the
output voltage.
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7.4 Device Functional Modes
7.4.1 Normal Operation
The device OUTPUT pin sources current necessary to make OUTPUT pin 1.25 V greater than ADJUST terminal
to provide output regulation.
7.4.2 Operation With Low Input Voltage
The device requires up to 3-V headroom (VI – VO) to operate in regulation. With less headroom, the device may
drop out and OUTPUT voltage is INPUT voltage minus drop out voltage.
7.4.3 Operation at Light Loads
The device passes its bias current to the OUTPUT pin. The load or feedback must consume this minimum
current for regulation or the output may be too high. A 250-Ω feedback resistor between OUTPUT and ADJUST
consumes the worst case minimum load current of 5 mA.
7.4.4 Operation in Self Protection
When an overload occurs, the device shuts down Darlington NPN output stage or reduces the output current to
prevent device damage. The device automatically resets from the overload. The output may be reduced or
alternate between on and off until the overload is removed.
10
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
In operation, the LM138 develops a nominal 1.25-V 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 I1 then flows through the output set resistor R2, giving an output voltage calculated with
Equation 1.
æ R2 ö
VOUT = VREF ç 1+
÷ + IADJR 2
è R2 ø
(1)
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Figure 15. Typical Application Circuit
Because 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 rises.
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8.2 Typical Applications
8.2.1 Constant 5-V Regulator
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Figure 16. Constant 5-V Regulator
8.2.1.1 Design Requirements
R1: Because the LM138 produces a typical 1.24 V potential between the OUTPUT and ADJUST pins, placing a
270-Ω resistor between them causes 4.6 mA to flow through R1 and R2.
R2: To achieve a 5-V output, the sum of the voltages across R1 and R2 must equal 5 V. Therefore, Vr2 must
equal 3.76 V when 4.6 mA is flowing through it. R2 = Vr2 / I = 3.76 V / 4.6 mA = ~820 Ω.
CIN: 0.1 µF of input capacitance helps filter out unwanted noise, especially if the regulator is located far from the
power supply filter capacitors.
COUT: The regulator is stable without any output capacitance, but adding a 1-µF capacitor improves the transient
response.
CADJ: A 10-µF capacitor bypassing the ADJUST pin to ground improves the regulators ripple rejection.
D1: Protection diode D1 is recommended if COUT is used. The diode provides a low-impedance discharge path to
prevent the capacitor from discharging into the output of the regulator (see Protection Diodes).
D2: Protection diode D2 is recommended if CADJ is used. The diode provides a low-impedance discharge path to
prevent the capacitor from discharging into the output of the regulator (see Protection Diodes).
Table 1 lists the design parameters for this typical application.
12
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Table 1. Design Parameters
PARAMETER
VALUE
Feedback resistor 1 (R1)
270 Ω
Feedback resistor 2 (R2)
820 Ω
Input capacitor (CIN)
0.1 µF
Output capacitor (COUT)
1 µF
Adjust capacitor(CADJ)
10 µF
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 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 bypassing when
adjustment or output capacitors are used but the above values eliminate the possibility 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.
8.2.1.2.2 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 240 Ω) must 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 15-V regulator with 0.05-Ω resistance between the regulator and load has a load regulation due to
line resistance of 0.05 Ω × IL. If the set resistor is connected near the load, the effective line resistance is 0.05 Ω
(1 + R2/R1) or in this case, 11.5 times worse.
Figure 17 shows the effect of resistance between the regulator and 240-Ω set resistor.
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Figure 17. 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.
8.2.1.2.3 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 20-A 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 discharges
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 25-A 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 15 V 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 50-Ω resistor which limits the peak
discharge current. No protection is needed for output voltages of 25-V or less and 10-µF capacitance. Figure 18
shows an LM138 with protection diodes included for use with outputs greater than 25 V and high values of output
capacitance.
14
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D1 protects against C1
D2 protects against C2
Figure 18. Regulator With Protection Diodes
8.2.1.3 Application Curves
Figure 19. Regulator Start-Up
Figure 20. Regulator Shutdown
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Figure 21. Regulator Response to Load Step
16
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8.3 System Examples
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Figure 22. Regulator and Voltage Reference
Figure 23. 1.2-V to 25-V Adjustable Regulator
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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.
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* Adjust for 3.75 across R1
**R1 = 240 Ω for LM138. R1, R2 as an assembly can be ordered
from Bourns:
MIL part no. 7105A-AT2-502
COMM part no. 7105A-AT7-502
Figure 24. Temperature Controller
Figure 25. Precision Power Regulator With
Low Temperature Coefficient
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LM138, LM338
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System Examples (continued)
Copyright © 2016, Texas Instruments Incorporated
Copyright © 2016, Texas Instruments Incorporated
Figure 26. Slow Turnon 15-V Regulator
†Solid tantalum
*Discharges C1 if output is shorted to ground
**R1 = 240 Ω for LM138
Figure 27. Adjustable Regulator With
Improved Ripple Rejection
Copyright © 2016, Texas Instruments Incorporated
Copyright © 2016, Texas Instruments Incorporated
*Sets maximum VOUT
**R1 = 240 Ω for LM138
Figure 28. High Stability 10-V Regulator
18
Figure 29. Digitally Selected Outputs
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System Examples (continued)
Copyright © 2016, Texas Instruments Incorporated
** Minimum output ≈ 1.2 V
Copyright © 2016, Texas Instruments Incorporated
* Minimum load—100 mA
Figure 30. 15-A Regulator
Figure 31. 5-V Logic Regulator With
Electronic Shutdown**
Copyright © 2016, Texas Instruments Incorporated
Copyright © 2016, Texas Instruments Incorporated
* R1 = 240 Ω, R2 = 5k for LM138
Full output current not available at high input-output voltages
Figure 32. Light Controller
Figure 33. 0 to 22-V Regulator
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System Examples (continued)
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Copyright © 2016, Texas Instruments Incorporated
Figure 34. 12-V Battery Charger
Figure 35. Adjustable Current Regulator
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Copyright © 2016, Texas Instruments Incorporated
Figure 36. Precision Current Limiter
20
Figure 37. 5-A Current Regulator
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LM138, LM338
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SNVS771C – MAY 1998 – REVISED DECEMBER 2016
System Examples (continued)
Copyright © 2016, Texas Instruments Incorporated
† Minimum load—10 mA
* All outputs within ±100 mV
Copyright © 2016, Texas Instruments Incorporated
Figure 38. Tracking Preregulator
Figure 39. Adjusting Multiple On-Card Regulators
With Single Control*
Copyright © 2016, Texas Instruments Incorporated
Use of RS allows low charging rates with fully charged battery.
**The 1000 µF is recommended to filter out input transients
Copyright © 2016, Texas Instruments Incorporated
AV = 1, RF = 10k, CF = 100 pF
AV = 10, RF = 100k, CF = 10 pF
Bandwidth ≥ 100 kHz
Distortion ≤ 0.1%
Use of RS allows low charging rates with fully charged battery.
**The 1000 µF is recommended to filter out input transients
Figure 40. Power Amplifier
Figure 41. Simple 12-V Battery Charger
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LM138, LM338
SNVS771C – MAY 1998 – REVISED DECEMBER 2016
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System Examples (continued)
Copyright © 2016, Texas Instruments Incorporated
* Set max charge current to 3 A
** THE 1000 µF is recommended to filter out input transients.
Copyright © 2016, Texas Instruments Incorporated
Figure 42. Adjustable 15-A Regulator
Figure 43. Current Limited 6-V Charger
Copyright © 2016, Texas Instruments Incorporated
* Minimum load—100 mA
Figure 44. 10-A Regulator
22
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LM138, LM338
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SNVS771C – MAY 1998 – REVISED DECEMBER 2016
9 Power Supply Recommendations
The input supply to LM138 and LM338 must be kept at a voltage level such that its maximum input to output
differential voltage rating is not exceeded. The minimum dropout voltage must also be met with extra headroom
when possible to keep the LM138 and LM338 in regulation. TI recommends a capacitor be placed at the input to
bypass noise.
10 Layout
10.1 Layout Guidelines
Some layout guidelines must be followed to ensure proper regulation of the output voltage with minimum noise.
Traces carrying the load current must be wide to reduce the amount of parasitic trace inductance and the
feedback loop from VOUT to ADJ must be kept as short as possible. To improve PSRR, a bypass capacitor can
be placed at the ADJ pin and must be placed as close as possible to the IC. In cases when VIN shorts to ground,
an external diode must be placed from VOUT to VIN to divert the surge current from the output capacitor and
protect the IC. Similarly, in cases when a large bypass capacitor is placed at the ADJ pin and VOUT shorts to
ground, an external diode must be placed from ADJ to VOUT to provide a path for the bypass capacitor to
discharge. These diodes must be placed close to the corresponding IC pins to increase their effectiveness.
10.2 Layout Example
Figure 45. LMx38 Layout
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SNVS771C – MAY 1998 – REVISED DECEMBER 2016
www.ti.com
11 Device and Documentation Support
11.1 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper
right corner, click on Alert me to register and receive a weekly digest of any product information that has
changed. For change details, review the revision history included in any revised document.
11.2 Related Links
The table below lists quick access links. Categories include technical documents, support and community
resources, tools and software, and quick access to sample or buy.
Table 2. Related Links
PARTS
PRODUCT FOLDER
SAMPLE & BUY
TECHNICAL
DOCUMENTS
TOOLS &
SOFTWARE
SUPPORT &
COMMUNITY
LM138
Click here
Click here
Click here
Click here
Click here
LM338
Click here
Click here
Click here
Click here
Click here
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
24
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Product Folder Links: LM138 LM338
PACKAGE OPTION ADDENDUM
www.ti.com
25-Aug-2017
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
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)
Call TI
Level-1-NA-UNLIM
-55 to 125
LM138K
STEELP+
LM338 MWC
NRND
WAFERSALE
YS
0
1
Green (RoHS
& no Sb/Br)
Call TI
Level-1-NA-UNLIM
-40 to 85
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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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