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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - DC DC Switching Regulators

Texas Instruments LM2671N-ADJ

Name: LM2671N-ADJ
Brand: Texas Instruments
SKU: LM2671N-ADJ
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: LM2671N-ADJ

Manufacturer:: Texas Instruments

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 8-DIP (0.300", 7.62mm)

Datasheet:: LM2671N-ADJ.pdf

Description:: IC REG BUCK ADJ 500MA 8PDIP

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Product details

Overview

LM2671N-ADJ from National Semiconductor is a monolithic 500mA step-down (buck) DC-DC switching regulator in an 8-pin DIP package, featuring a 260 kHz fixed-frequency oscillator, internal DMOS switch with 0.25 Ω R_DS(ON), adjustable output range of 1.21 V to 37 V, and ±1.5% output voltage tolerance over line and load conditions. It delivers >90% efficiency and supports soft-start, frequency synchronization, and TTL-compatible shutdown - used in industrial power supplies requiring compact, high-efficiency pre-regulation.

For engineers reviewing the LM2671N-ADJ datasheet, LM2671N-ADJ pinout, LM2671N-ADJ application, or LM2671N-ADJ equivalent, key selection criteria include input voltage range (6.5 V to 40 V), guaranteed 500 mA load capability, feedback reference voltage (1.21 V), thermal shutdown protection, and compatibility with standard off-the-shelf inductors and Schottky diodes.

Technical Context

The LM2671N-ADJ implements a current-mode buck topology with an integrated 0.25 Ω DMOS power switch and patented internal frequency compensation. Its 260 kHz fixed-frequency oscillator enables predictable EMI filtering and consistent external component sizing.

Operation relies on feedback regulation via the FB pin referenced to a precise 1.21 V internal bandgap, with soft-start controlled by an external capacitor and shutdown managed through TTL-level logic on the ON/OFF pin. Protection includes cycle-by-cycle current limiting and thermal shutdown.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Current	Guaranteed 500 mA continuous load current - sufficient for powering microcontrollers, sensors, and analog circuitry without external current boosting.
Input Voltage Range	6.5 V to 40 V - supports wide-range unregulated inputs such as automotive batteries, industrial 24 V rails, and telecom supplies.
Feedback Reference Voltage	1.210 V (±1.5% over temp and load) - sets output accuracy when programming with external resistor divider (V_OUT = 1.21 × (1 + R2/R1)).
Switching Frequency	260 kHz (±10%) - balances efficiency and filter size; enables use of standard 47–100 µH inductors and low-ESR tantalum or ceramic output capacitors.
R_DS(ON)	0.25 Ω typical - minimizes conduction loss at full load, contributing to >90% peak efficiency and reducing thermal stress on PCB copper.
Quiescent Current	2.5 mA typical (3.6 mA max) - ensures low no-load power draw in always-on systems; standby current drops to 50 µA in shutdown mode.
Protection Features	Thermal shutdown + cycle-by-cycle current limit - prevents damage during overload, short-circuit, or inadequate heatsinking conditions.

Pinout & Package

LM2671N-ADJ is housed in an 8-pin plastic dual in-line package (DIP), with through-hole mounting and industry-standard MO8A/N08E footprint. Thermal resistance θ_JA is 95 °C/W with ~1 in² copper area.

Pin	Circuit Role	Design Meaning
1 (VIN)	Input Power Supply	Accepts 6.5 V to 40 V DC; requires local 22 µF tantalum bypass capacitor close to pin to suppress transients.
2 (GND)	Power Ground	Common return for input capacitor, output capacitor, and catch diode; must be low-impedance connection to minimize noise and voltage drop.
3 (SYNC)	Frequency Synchronization Input	Accepts external clock signal up to 400 kHz; enables synchronized operation in multi-regulator systems to reduce beat frequencies and EMI.
4 (FB)	Feedback Input	High-impedance node sensing output voltage via resistor divider; bias current <85 nA ensures minimal divider error.
5 (ON/OFF)	Shutdown Control	TTL-compatible input; drives device into 50 µA standby when pulled ≤0.8 V; threshold is 1.4 V typical with 20 µA input current.
6 (SW)	Switch Node	Drives external catch diode and inductor; switches between VIN and GND at 260 kHz; peak voltage reaches VIN + 0.7 V during flyback.
7 (BOOST)	Bootstrap Capacitor Connection	Connects to 0.01 µF ceramic capacitor between SW and BOOST to generate gate drive voltage for internal DMOS switch.
8 (SS)	Soft-Start Timing	Controls startup ramp rate via external capacitor; 0.63 V threshold and 4.5 µA charging current set t_SS ≈ 0.14 × C_SS (ms).

Key Features

Feature	Design Value
Integrated 0.25 Ω DMOS Switch	Eliminates need for external MOSFET and driver, reducing BOM count and layout complexity while maintaining >90% efficiency at 500 mA.
Patented Internal Frequency Compensation	Removes requirement for external compensation network - simplifies design and improves stability across all operating conditions.
Adjustable Output (1.21 V to 37 V)	Enables single IC to support diverse system voltages via two-resistor feedback divider - ideal for configurable power rails and legacy voltage standards.
260 kHz Fixed Switching Frequency	Provides predictable EMI profile and allows use of cost-effective, widely available standard inductors (e.g., 47–100 µH) without custom magnetics.
TTL-Compatible Shutdown & Soft-Start	Supports sequenced power-up in multi-rail systems and prevents inrush current damage to downstream components or input supply.

Applications

Industrial Motor Drive Power Supply	Programmable Logic Controller (PLC) I/O Module
Use Scenario: Powers isolated 5 V or 12 V logic rails from 24 V DC field bus in motor control cabinets with ambient temperatures up to +70 °C. IC Role / Device Role / Timing Role: Primary buck regulator delivering stable, ripple-controlled voltage to FPGA configuration circuitry and digital isolators. Use Value: High efficiency (>90%) reduces heat buildup in sealed enclosures; 40 V max input accommodates 24 V bus transients per IEC 61000-4-4.	Use Scenario: Generates 3.3 V and 5 V auxiliary supplies for microcontroller, ADC, and optocoupler interfaces in modular PLC backplanes. IC Role / Device Role / Timing Role: Adjustable-output buck converter configured for multiple rail voltages using resistor-programmed feedback networks. Use Value: ±1.5% output tolerance ensures reliable ADC reference and logic-level compatibility; soft-start prevents brownout during hot-swap insertion.
Telecom Line Card Power Pre-Regulator	Test & Measurement Equipment Power Stage
Use Scenario: Steps down -48 V or +48 V telecom supply to intermediate 12 V or 15 V rail feeding linear post-regulators for analog signal chains. IC Role / Device Role / Timing Role: High-input-voltage buck stage providing efficient, low-noise pre-regulation before LDOs. Use Value: 6.5 V to 40 V input range covers both positive and negative-derived rails; 260 kHz switching avoids sensitive audio/RF bands.	Use Scenario: Supplies precision analog front-ends (op-amps, DACs, multiplexers) in benchtop instruments requiring low-noise, stable bias voltages. IC Role / Device Role / Timing Role: Adjustable buck regulator configured for 2.5 V, 3.3 V, or 5 V outputs with tight tolerance and low ripple. Use Value: 1.21 V reference and low FB bias current (<85 nA) enable high-accuracy resistor-divider programming; thermal shutdown protects against probe misconnection faults.

Industrial Motor Drive Power Supply

Programmable Logic Controller (PLC) I/O Module

Use Scenario: Powers isolated 5 V or 12 V logic rails from 24 V DC field bus in motor control cabinets with ambient temperatures up to +70 °C.

IC Role / Device Role / Timing Role: Primary buck regulator delivering stable, ripple-controlled voltage to FPGA configuration circuitry and digital isolators.

Use Value: High efficiency (>90%) reduces heat buildup in sealed enclosures; 40 V max input accommodates 24 V bus transients per IEC 61000-4-4.

Use Scenario: Generates 3.3 V and 5 V auxiliary supplies for microcontroller, ADC, and optocoupler interfaces in modular PLC backplanes.

IC Role / Device Role / Timing Role: Adjustable-output buck converter configured for multiple rail voltages using resistor-programmed feedback networks.

Use Value: ±1.5% output tolerance ensures reliable ADC reference and logic-level compatibility; soft-start prevents brownout during hot-swap insertion.

Telecom Line Card Power Pre-Regulator

Test & Measurement Equipment Power Stage

Use Scenario: Steps down -48 V or +48 V telecom supply to intermediate 12 V or 15 V rail feeding linear post-regulators for analog signal chains.

IC Role / Device Role / Timing Role: High-input-voltage buck stage providing efficient, low-noise pre-regulation before LDOs.

Use Value: 6.5 V to 40 V input range covers both positive and negative-derived rails; 260 kHz switching avoids sensitive audio/RF bands.

Use Scenario: Supplies precision analog front-ends (op-amps, DACs, multiplexers) in benchtop instruments requiring low-noise, stable bias voltages.

IC Role / Device Role / Timing Role: Adjustable buck regulator configured for 2.5 V, 3.3 V, or 5 V outputs with tight tolerance and low ripple.

Use Value: 1.21 V reference and low FB bias current (<85 nA) enable high-accuracy resistor-divider programming; thermal shutdown protects against probe misconnection faults.

Equivalent & Alternatives

The following parts are listed as comparable options for similar buck regulator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM2671M-ADJ	Same silicon die, but in SO-8 surface-mount package (θ_JA = 105 °C/W); lacks DIP's mechanical robustness and hand-solderability.	Better suited for space-constrained PCBs and automated assembly; less suitable for prototyping or high-vibration environments.	Select LM2671M-ADJ only when board real estate or reflow process mandates SO-8; verify thermal performance with reduced copper area.
LM2596-ADJ	Higher 3 A output current, 150 kHz switching, wider 4–40 V input, but larger solution size and lower efficiency at light loads.	Preferred for higher-current applications (>500 mA); not drop-in due to different pinout, compensation, and external component values.	Choose LM2596-ADJ when load exceeds 500 mA or input dips below 6.5 V; redesign layout and recalculate inductor/capacitor values.

Compared with LM2671M-ADJ and LM2596-ADJ, the LM2671N-ADJ offers optimal balance of through-hole manufacturability, thermal performance in open-frame designs, and proven 260 kHz EMI behavior - making it preferred for industrial prototyping, low-volume production, and legacy-compatible upgrades.

Availability

LM2671N-ADJ is available at Aetrix Electronics and suitable for industrial motor drives, programmable logic controllers, telecom line cards, and test equipment requiring stable component supply with long-term obsolescence management.

Supply support for LM2671N-ADJ includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

National Semiconductor was a U.S.-based semiconductor company specializing in analog and power management ICs, acquired by Texas Instruments in 2011; its SIMPLE SWITCHER® portfolio remains widely deployed in industrial and telecom infrastructure.

The LM2671 series was designed as a monolithic, easy-to-use buck regulator family targeting cost-sensitive, high-reliability applications where minimal external components and proven thermal behavior were critical - especially in DIP-based control modules and legacy replacement designs.

FAQ

What is the minimum input voltage required for stable operation of the LM2671N-ADJ?

The LM2671N-ADJ specifies an operating input voltage range of 6.5 V to 40 V. Below 6.5 V, the internal circuitry cannot maintain regulation or sustain switching; dropout occurs well before this point depending on output voltage and load. For a 5 V output at 500 mA, practical minimum input is ~7.5 V to ensure adequate headroom across temperature and line variations. The LM2671N-ADJ does not support ultra-low-input applications like 3.3 V or 5 V input rails.

Can the LM2671N-ADJ be synchronized to an external clock, and what are the interface requirements?

Yes, the LM2671N-ADJ supports frequency synchronization via Pin 3 (SYNC). It accepts a square-wave or sine-wave signal with peak-to-peak amplitude ≥3 V and frequency up to 400 kHz. A simple RC filter (1 kΩ + 100 pF) is recommended at the SYNC pin to reject noise. Synchronization allows coordinated switching in multi-rail systems to avoid beat frequencies and simplify EMI filtering - a capability confirmed in the LM2671N-ADJ datasheet Figure 7 and Electrical Characteristics table.

What is the purpose of the BOOST pin on the LM2671N-ADJ, and how must it be connected?

The BOOST pin on the LM2671N-ADJ provides the gate-drive voltage for the internal DMOS switch. It must be connected to a 0.01 µF, 50 V ceramic capacitor between BOOST and the SW (switch) pin. This forms a bootstrap charge pump that elevates the gate voltage above VIN during high-side conduction. Omitting or undersizing this capacitor causes weak switching, excessive R_DS(ON), thermal runaway, and potential failure. The LM2671N-ADJ will not function correctly without this capacitor properly installed.

How does the soft-start function work on the LM2671N-ADJ, and what capacitor value is recommended for a 10 ms startup time?

The LM2671N-ADJ uses an internal 4.5 µA current source to charge an external capacitor on the SS (Pin 8) until it reaches a 0.63 V threshold, at which point full regulation begins. For a 10 ms soft-start time, the required capacitor is C_SS = t_SS / 0.14 ≈ 71 nF - a standard 68 nF or 75 nF capacitor is appropriate. Avoid values between 33 nF and 1 µF, as they may cause output overshoot during startup, especially under light or no-load conditions.

Is the LM2671N-ADJ RoHS-compliant, and what is its lead finish specification?

The LM2671N-ADJ was originally manufactured prior to RoHS enforcement and uses a leaded (SnPb) finish on its 8-pin DIP package. National Semiconductor did not release a RoHS-compliant variant of the N-suffix DIP version; RoHS alternatives require migration to SO-8 (LM2671M-ADJ) or newer families like LM2596. Aetrix Electronics supplies only original-spec LM2671N-ADJ units with SnPb leads, compliant with exemption 7a (lead in high-melting-temperature type solders) for industrial applications where reworkability and reliability are prioritized over RoHS compliance.

LM2671N-ADJ Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: SIMPLE SWITCHER®

Package/Case:: 8-DIP (0.300", 7.62mm)

Packaging:: Tube

Product Status:: Obsolete

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable

Number of Outputs:: 1

Voltage - Input (Min):: 6.5V

Voltage - Input (Max):: 40V

Voltage - Output (Min/Fixed):: 1.21V

Voltage - Output (Max):: 37V

Current - Output:: 500mA

Frequency - Switching:: 260kHz

Synchronous Rectifier:: No

Operating Temperature:: -40°C ~ 125°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 8-PDIP

LM2671N-ADJ FAQ

1.How can I place an order for LM2671N-ADJ through Aetrix?

Please submit a Request for Quotation (RFQ) for LM2671N-ADJ on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for LM2671N-ADJ reliable?

The price and inventory of LM2671N-ADJ are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LM2671N-ADJ is usually 5 days.

3.What payment methods are accepted for LM2671N-ADJ?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LM2671N-ADJ transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for LM2671N-ADJ?

LM2671N-ADJ orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your LM2671N-ADJ order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for LM2671N-ADJ?

For technical support, including LM2671N-ADJ datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LM2671N-ADJ requirements.

6.How does Aetrix verify that LM2671N-ADJ is sourced from the original manufacturer or authorized distributors?

All LM2671N-ADJ products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LM2671N-ADJ meets industry standards.

7.What is the process for return or replacement of LM2671N-ADJ?

All LM2671N-ADJ units undergo pre-shipment inspection (PSI). If there is an issue with LM2671N-ADJ, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The LM2671N-ADJ part is unused and in its original packaging.

Return procedure for LM2671N-ADJ:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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