Texas Instruments LM2671MX-ADJ

Overview

LM2671MX-ADJ from Texas Instruments (formerly National Semiconductor) is a monolithic 500mA step-down DC-DC switching regulator in SO-8 package, featuring an internal 0.25Ω DMOS switch, 260 kHz fixed-frequency oscillator, and adjustable output voltage range of 1.21V to 37V. It delivers >90% efficiency at full load and supports soft-start, frequency synchronization, and TTL-compatible shutdown - used in industrial power supplies requiring compact, high-efficiency buck conversion.

For engineers reviewing the LM2671MX-ADJ datasheet, LM2671MX-ADJ pinout, LM2671MX-ADJ application, or LM2671MX-ADJ equivalent, key selection criteria include input voltage range (6.5V–40V), guaranteed 500mA output current, ±1.5% output voltage tolerance over line/load/temperature, thermal shutdown protection, and compatibility with standard off-the-shelf inductors and Schottky diodes.

Technical Context

The LM2671MX-ADJ implements a synchronous-buck topology using an integrated DMOS power switch and patented internal frequency compensation (U.S. Pat. Nos. 5,382,918 and 5,514,947). Its 260 kHz switching frequency enables use of small external magnetics while maintaining low EMI and predictable ripple performance.

Feedback regulation is based on a precision 1.21V reference (±1.5% max tolerance), with bias current <85 nA and soft-start threshold at 0.63V. The device features active current limiting (0.62–1.25A), thermal shutdown, and standby quiescent current of 50 μA typical when disabled via the ON/OFF pin.

Key Specifications

Pinout & Package

LM2671MX-ADJ is housed in an 8-pin SOIC (SO-8) surface-mount package per NSC MO8A/N08E drawing, with exposed pad not electrically connected. Thermal resistance θ_JA = 105°C/W with standard PCB copper layout.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM2576-ADJ, LM2671MX-ADJ offers 260 kHz operation for smaller magnetics and better transient response; compared with TPS54302DDCR, it supports wider input (6.5–40 V) and simpler external component count, though at lower current rating.

Availability

LM2671MX-ADJ is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, and test equipment requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for LM2671MX-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

Texas Instruments acquired National Semiconductor in 2011 and maintains full technical and manufacturing continuity for the SIMPLE SWITCHER® portfolio.

The LM2671MX-ADJ belongs to the SIMPLE SWITCHER® family of easy-to-use DC-DC regulators, designed specifically to simplify power supply design for engineers without deep power electronics expertise.

FAQ

What is the minimum input voltage required for stable operation of the LM2671MX-ADJ?

The LM2671MX-ADJ specifies an operating input voltage range of 6.5 V to 40 V. Below 6.5 V, the internal circuitry may not bias correctly, causing erratic switching or dropout. At 6.5 V input, the maximum duty cycle (95%) limits the lowest achievable output voltage - for example, a 1.21 V output requires ≥1.27 V input to sustain regulation. Always verify minimum input under worst-case load and temperature conditions using the datasheet's dropout curves.

Can the LM2671MX-ADJ be synchronized to an external clock, and what are the electrical requirements?

Yes, the LM2671MX-ADJ supports external synchronization via its SYNC pin (Pin 3). It accepts TTL/CMOS-compatible signals up to 400 kHz. For reliable locking, apply a square wave with ≥3 V_PP, 50% duty cycle, and use a 1 kΩ series resistor plus 100 pF capacitor to ground at the SYNC pin to filter noise. The internal sync comparator triggers at 1.4 V threshold; exceeding 400 kHz may cause missed cycles or instability.

How is the output voltage programmed on the LM2671MX-ADJ, and what resistor tolerance is recommended?

The LM2671MX-ADJ uses a resistor divider (R1 from FB to GND, R2 from VOUT to FB) to set output voltage per V_OUT = 1.21 × (1 + R2/R1). National Semiconductor recommends R1 = 1 kΩ to 1.5 kΩ (1% metal film) to minimize noise pickup and drift. For a 12 V output, R2 = 8.91 kΩ (1%); for 5 V, R2 = 3.15 kΩ (1%). Avoid carbon composition or thick-film resistors due to poor tempcos and long-term drift.

Does the LM2671MX-ADJ require a heatsink under full 500 mA load?

No external heatsink is required. With θ_JA = 105°C/W and typical efficiency >90% at 12 V input/5 V output, power dissipation remains below 0.25 W at full load. Standard 1-inch² PCB copper pour around the SO-8 package provides sufficient thermal path to keep junction temperature within the −40°C to +125°C operating range. Thermal shutdown activates only under sustained overload or inadequate PCB copper.

What type of catch diode is recommended for use with the LM2671MX-ADJ, and why?

A Schottky diode rated ≥3 A average current and ≥50 V reverse voltage is recommended - e.g., IR 30WQ05F (3 A, 50 V) or MBRS340 (3 A, 40 V). Schottky diodes minimize forward voltage drop (typically 0.4–0.5 V), reducing conduction loss and improving overall efficiency. Fast recovery is unnecessary since the LM2671MX-ADJ's 260 kHz frequency and internal switch timing are optimized for Schottky characteristics; PN diodes increase losses and risk thermal runaway.