Texas Instruments LM2678SDX-3.3

Overview

LM2678SDX-3.3 from Texas Instruments is a monolithic step-down (buck) DC/DC switching regulator delivering up to 5 A output current with fixed 3.3 V output, 8–40 V input range, 260 kHz fixed-frequency operation, and ±2% output voltage tolerance over full line/load/temperature. It integrates a 120 mΩ DMOS high-side switch and supports ON/OFF control for low-power standby.

For engineers reviewing the LM2678SDX-3.3 datasheet, LM2678SDX-3.3 pinout, LM2678SDX-3.3 application, or LM2678SDX-3.3 equivalent, key selection criteria include its 3.3 V fixed output accuracy, thermal shutdown and current limiting protection, 50 µA standby quiescent current, and compatibility with standard off-the-shelf inductors and Schottky diodes in high-efficiency (>90%) power conversion designs.

Technical Context

The LM2678SDX-3.3 implements a fixed-frequency PWM buck controller with internal 260 kHz oscillator and integrated 120 mΩ DMOS high-side switch. Its feedback loop uses a direct connection from FB pin to output for fixed 3.3 V regulation, eliminating external resistor dividers.

It operates across –40°C to +125°C junction temperature, features built-in thermal shutdown and cycle-by-cycle current limiting, and enters shutdown mode when ON/OFF pin voltage drops below 0.8 V-reducing quiescent current to 50 µA while maintaining fast wake-up capability.

Key Specifications

Pinout & Package

LM2678SDX-3.3 is supplied in the KTW (TO-263-7) package: 10.1 mm × 15.24 mm surface-mount outline with exposed thermal pad (DAP) connected to GND. The DAP must be soldered to a PCB copper area for thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2678SDX-3.3, LM2675SD-3.3 provides identical regulation accuracy and frequency but reduced current capacity and thermal performance, while TPS54560BDDAR trades fixed-output simplicity for programmability and package compactness-making LM2678SDX-3.3 optimal for high-current, drop-in 3.3 V replacement where layout reuse and minimal BOM count are critical.

Availability

LM2678SDX-3.3 is available at Aetrix Electronics and suitable for industrial PLC power supplies, automotive body control modules, and embedded system preregulators requiring stable component supply, long-lifecycle support, and proven thermal reliability in high-current DC/DC conversion.

Supply support for LM2678SDX-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 LM2678 series belongs to TI's SIMPLE SWITCHER® family-designed specifically for ease-of-use, high-efficiency buck conversion using minimal external components and industry-standard passive parts.

FAQ

What is the maximum output current rating of the LM2678SDX-3.3?

The LM2678SDX-3.3 is rated for up to 5 A continuous output current under recommended operating conditions (T_J ≤ 125°C, adequate PCB copper area). Actual achievable current depends on input voltage, ambient temperature, and thermal design-TI specifies 5 A with ≥0.4896 in² of 1 oz. copper for the KTW package. The device includes cycle-by-cycle current limiting that activates above ~6.1 A typical to protect against overload.

Does the LM2678SDX-3.3 require external feedback resistors to set its output voltage?

No. The LM2678SDX-3.3 is a fixed-output variant with internal resistor divider network calibrated for 3.3 V. Pin 6 (FB) must be connected directly to the output capacitor terminal-no external resistors are needed. This simplifies layout, improves long-term accuracy, and eliminates resistor tolerance and drift effects that affect adjustable versions like the LM2678-ADJ.

What is the purpose of the CB pin on the LM2678SDX-3.3, and what capacitor value is recommended?

The CB (bootstrap capacitor) pin on the LM2678SDX-3.3 provides gate drive voltage for the internal high-side DMOS switch. It must be connected via a 100 nF (0.01 µF) X7R ceramic capacitor between CB and SW (pin 1). This capacitor charges during the low-side conduction phase and supplies the gate-source voltage needed to fully enhance the high-side FET-ensuring low R_DS(on) and high efficiency. Poor CB placement or undersized capacitance causes erratic switching or thermal runaway.

How does the ON/OFF pin function on the LM2678SDX-3.3, and what voltage thresholds trigger enable/disable?

The ON/OFF pin (pin 7) controls regulator operation: applying ≥1.4 V (typical) enables switching and output regulation, while ≤0.8 V (typical) forces shutdown with 50 µA standby current. The pin has an internal ~20 µA pull-up and 7 V Zener clamp. It can be driven directly by a microcontroller GPIO or open-collected transistor. Floating the pin enables the device by default. This feature supports system-level power sequencing and low-power sleep modes without external logic.

Can the LM2678SDX-3.3 operate from a 5 V input supply?

No. The LM2678SDX-3.3 has a minimum recommended input voltage of 8 V per its absolute maximum and operating conditions specifications. Operation below 8 V may result in failure to start, unstable regulation, or excessive dropout-especially under load. For 5 V input applications, consider alternatives such as the TPS54331 (3 A, 3.5–28 V input) or LM2672MX-3.3 (similar architecture, 6.5–40 V input with lower min).