Texas Instruments LM2679T-3.3

Overview

LM2679T-3.3 from Texas Instruments is a monolithic 5A step-down (buck) DC/DC voltage regulator with fixed 3.3V output, 260 kHz fixed-frequency internal oscillator, 120 mΩ DMOS power switch, and resistor-programmable current limit (3A–7A). It operates from 8V to 40V input and delivers ±2% output tolerance over line/load/temperature for industrial power supply pre-regulation.

For engineers reviewing the LM2679T-3.3 datasheet, LM2679T-3.3 pinout, LM2679T-3.3 application, or LM2679T-3.3 equivalent, key selection criteria include input voltage range, peak switch current programmability, thermal resistance in TO-220 package, softstart timing control, and compatibility with standard off-the-shelf inductors and low-ESR output capacitors.

Technical Context

The LM2679T-3.3 integrates a PWM controller, 260 kHz oscillator, and 120 mΩ DMOS power switch in a single TO-220-7 package. Its feedback loop uses an internal 1.21V reference and two-stage high-gain amplifier, eliminating external resistors for fixed-output versions.

Current limiting is implemented via a resistor (RADJ) connected between CURRENT ADJ pin and ground, setting peak switch current per ICL = 37,125 / RADJ. Softstart is controlled by a capacitor on the SOFTSTART pin, linearly ramping duty cycle using a 3.7 µA internal current source and 0.63 V threshold.

Key Specifications

Pinout & Package

LM2679T-3.3 is housed in a 7-lead TO-220 package (Package Number NDZ0007B), with exposed tab thermally and electrically connected to GND. The package provides θ_JA = 45°C/W with 4 in² copper area, enabling 5 A operation without forced air.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2679T-3.3, LM2596T-3.3 offers lower cost but reduced current capability and no current-limit programming, while TPS54560B extends input range and frequency but increases design complexity and requires external compensation - making LM2679T-3.3 optimal for robust 8–40 V, 5 A fixed-output applications with minimal external parts.

Availability

LM2679T-3.3 is available at Aetrix Electronics and suitable for industrial automation power supplies, battery-powered instrumentation, and programmable logic controller (PLC) I/O modules requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM2679T-3.3 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 is a global semiconductor leader specializing in analog, embedded processing, and power management ICs, with decades of expertise in high-reliability power conversion solutions.

The LM2679 series belongs to TI's SIMPLE SWITCHER® family - designed specifically for easy-to-implement, high-efficiency step-down regulators targeting industrial, automotive, and telecom power systems where minimal external components and proven reliability are essential.

FAQ

What is the maximum input voltage rating for the LM2679T-3.3?

The absolute maximum input voltage for the LM2679T-3.3 is 45 V, but the recommended operating range is 8 V to 40 V. Exceeding 40 V may trigger internal protection or reduce reliability. The device's 120 mΩ DMOS switch and integrated thermal shutdown ensure safe operation within this range, and the LM2679T-3.3 datasheet specifies full electrical performance only between 8 V and 40 V under all load and temperature conditions.

Does the LM2679T-3.3 require external feedback resistors to set its output voltage?

No, the LM2679T-3.3 does not require external feedback resistors. It is a fixed-output variant with internal resistor divider network calibrated for 3.3 V ±2%. Pin 6 (FB) must be connected directly to the output node to close the regulation loop. Adding external resistors would disrupt the factory-trimmed reference and degrade accuracy - the LM2679T-3.3 is explicitly designed for plug-and-play operation without feedback component selection.

How is the current limit programmed on the LM2679T-3.3?

The current limit on the LM2679T-3.3 is programmed using a single resistor (RADJ) connected between the CURRENT ADJ pin (Pin 5) and GND. The peak switch current follows I_CL = 37,125 / R_ADJ, where R_ADJ is in ohms and I_CL is in amperes. For example, a 5.6 kΩ resistor sets I_CL ≈ 6.3 A. This feature allows designers to match the current limit precisely to their inductor saturation rating and diode surge capability - a key differentiator of the LM2679T-3.3 versus non-adjustable alternatives.

What package type is used for the LM2679T-3.3, and how is thermal performance affected by PCB layout?

The LM2679T-3.3 uses a 7-lead TO-220 package (NDZ0007B) with the exposed tab electrically and thermally connected to GND. Thermal resistance θ_JA improves from 65°C/W (no copper) to 45°C/W with ~4 in² of 1 oz. copper, enabling full 5 A operation without a heatsink. Proper layout - including wide GND traces, multiple vias under the tab, and minimized trace inductance on VIN/VSW - is essential to maintain the LM2679T-3.3's specified efficiency and thermal safety margin.

Can the LM2679T-3.3 be used with ceramic output capacitors only?

Yes, the LM2679T-3.3 supports ceramic output capacitors, but total capacitance and ESR must meet stability requirements. The datasheet recommends ≥2 × 180 µF/16 V for 3.3 V output - typically achieved with parallel ceramic + tantalum or aluminum polymer. Pure ceramic banks require careful attention to minimum ESR (≥5 mΩ) and capacitance value to avoid control-loop instability; TI's AN-1187 and LM267X Made Simple software provide validated ceramic-only configurations for the LM2679T-3.3.