LM338

ACTIVE

5-A, 40-V, low-IQ, adjustable linear voltage regulator

Product details

Output options Adjustable Output Iout (max) (A) 5 Vin (max) (V) 40 Vin (min) (V) 4.2 Vout (max) (V) 32 Vout (min) (V) 1.24 Rating Catalog Noise (µVrms) 37 PSRR at 100 KHz (dB) 10 Iq (typ) (mA) 0.045 Thermal resistance θJA (°C/W) 23 Load capacitance (min) (µF) 0 Regulated outputs (#) 1 Accuracy (%) 2.4 Dropout voltage (Vdo) (typ) (mV) 2700 Operating temperature range (°C) 0 to 125
Output options Adjustable Output Iout (max) (A) 5 Vin (max) (V) 40 Vin (min) (V) 4.2 Vout (max) (V) 32 Vout (min) (V) 1.24 Rating Catalog Noise (µVrms) 37 PSRR at 100 KHz (dB) 10 Iq (typ) (mA) 0.045 Thermal resistance θJA (°C/W) 23 Load capacitance (min) (µF) 0 Regulated outputs (#) 1 Accuracy (%) 2.4 Dropout voltage (Vdo) (typ) (mV) 2700 Operating temperature range (°C) 0 to 125
TO-220 (NDE) 3 46.5328 mm² 10.16 x 4.58
  • 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
  • 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

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.

A unique feature of the LM138 family is time-dependent 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 suffix are packaged in a standard steel TO-CAN package, while those with a 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.

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.

A unique feature of the LM138 family is time-dependent 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 suffix are packaged in a standard steel TO-CAN package, while those with a 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.

Download View video with transcript Video

Similar products you might be interested in

open-in-new Compare alternates
Same functionality with different pin-out to the compared device
TPS7A19 ACTIVE 450-mA, 40-V, low-IQ, adjustable low-dropout voltage regulator with power good & enable A smaller (9 mm2), 40-V LDO with power good

Technical documentation

star =Top documentation for this product selected by TI
No results found. Please clear your search and try again.
View all 10
Type Title Date
* Data sheet LM138 and LM338 5-Amp Adjustable Regulators datasheet (Rev. C) PDF | HTML 19 Dec 2016
Application note A Topical Index of TI LDO Application Notes (Rev. F) 27 Jun 2019
Application note AN-103 LM340 Series Three Terminal Positive Regulators (Rev. A) 06 May 2013
Application note AN-1148 Linear Regulators: Theory of Operation and Compensation (Rev. B) 06 May 2013
Application note Method For Cal Output Voltage Tolerances in Adj Regs (Rev. A) 05 May 2013
More literature Die D/S LM338 MDC 5 Amp Adj Regulator 25 Sep 2012
Application note Packaging Limits Range of Linear Regulators 08 May 2010
Application note Digital Designer's Guide to Linear Voltage Regulators & Thermal Mgmt (LDO) (Rev. A) 04 Jun 2008
Application note Add Kelvin Sensing and Parallel Capability to 3-Terminal Regulators 03 Oct 2002
Application note Understanding the Terms and Definitions of LDO Voltage Regulators 21 Oct 1999

Design & development

For additional terms or required resources, click any title below to view the detail page where available.

Package Pins CAD symbols, footprints & 3D models
TO-220 (NDE) 3 Ultra Librarian

Ordering & quality

Information included:
  • RoHS
  • REACH
  • Device marking
  • Lead finish/Ball material
  • MSL rating/Peak reflow
  • MTBF/FIT estimates
  • Material content
  • Qualification summary
  • Ongoing reliability monitoring
Information included:
  • Fab location
  • Assembly location

Recommended products may have parameters, evaluation modules or reference designs related to this TI product.

Support & training

TI E2E™ forums with technical support from TI engineers

Content is provided "as is" by TI and community contributors and does not constitute TI specifications. See terms of use.

If you have questions about quality, packaging or ordering TI products, see TI support. ​​​​​​​​​​​​​​

Videos