STMicroelectronics L6981NDR

Overview

L6981NDR from STMicroelectronics is a synchronous monolithic step-down DC-DC converter in SO8 package, delivering up to 1.5 A output current with 20 μA quiescent current (LCM mode), 3.5–38 V input range, and adjustable/fixed 3.3 V or 5 V output. It implements peak current mode control with internal compensation and supports light-load optimization via LCM (high efficiency) or LNM (low noise) modes - used in industrial 24 V bus power supplies and always-on sensor nodes.

For engineers reviewing the L6981NDR datasheet, L6981NDR pinout, L6981NDR application, or L6981NDR equivalent, key selection criteria include VIN compatibility (up to 38 V), EN/CLKIN dual-function pin behavior, soft-start timing (1.3 ms), OVP trip at 120% VREF, and thermal shutdown at 165 °C - all critical for robust 24 V industrial and battery-powered designs.

Technical Context

The L6981NDR uses peak current mode architecture with integrated slope compensation to prevent subharmonic oscillation. Its error amplifier features an internal compensation network, eliminating external components while maintaining stability across 0.85–VIN output range.

It offers two operational modes: LCM enables pulse-skipping for <1 mA IQ_VIN at light load (fixed-VOUT versions draw only 1–6 μA from VIN), while LNM enforces constant-frequency PWM (360–440 kHz) with external clock synchronization capability (200–500 kHz range) and reduced output ripple for noise-sensitive applications like smart meters and robot cleaners.

Key Specifications

Pinout & Package

Package: SO8 (Small Outline, 8-pin, surface-mount). Exposed pad variant not specified; standard SO8 thermal resistance R_thJA = 65 °C/W on 2-layer 2-oz Cu demo board.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMR14015QPWPRQ1 and TPS54202HDDCR, the L6981NDR uniquely combines 38 V input rating, 20 μA LCM IQ, built-in OVP, and dual-mode light-load operation - making it optimal for cost-sensitive, long-duration 24 V industrial and metering designs where reliability and efficiency coexist.

Availability

L6981NDR is available at Aetrix Electronics and suitable for industrial 24 V bus power systems, smart meter power management, and decentralized sensor nodes requiring stable component supply with long-term lifecycle assurance.

Supply support for L6981NDR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The L6981 belongs to ST's high-voltage synchronous buck regulator product line, designed specifically for robust, low-quiescent-current DC-DC conversion in 24 V industrial and battery-powered equipment.

FAQ

What is the difference between L6981NDR and L6981ADJ variants?

The L6981NDR is a fixed 5 V output version with VOUT/FB pin internally connected to a precision 0.85 V reference and resistor divider, delivering regulated 5.0 V ±0.5% across temperature. The L6981ADJ uses the same SO8 package but leaves the FB pin accessible for external resistor programming of any output from 0.85 V to VIN, enabling flexible system-level voltage scaling.

Can L6981NDR synchronize to an external clock in all operating modes?

No - external clock synchronization via the EN/CLKIN pin is supported only in LNM (Low Noise Mode) versions. The L6981NDR is an LNM-part-numbered device, so it accepts 200–500 kHz external clocks with 2.3 V amplitude and ≥20 ns pulse width. LCM versions ignore CLKIN functionality and use EN solely for enable/disable control.

How does the switch-over feature reduce input current in fixed-output versions?

In fixed-VOUT versions like L6981NDR, the switch-over feature powers internal circuitry from VOUT instead of VIN when enabled, reducing total input current to IQ_VIN = IQ_OPVIN + (VOUT/VIN) × IQ_VOUT/η. This cuts typical input quiescent current from ~300 μA to just 1–6 μA - critical for extending battery life in always-on applications.

Is the SO8 package thermally enhanced, and what is its maximum power dissipation?

The L6981NDR uses standard SO8 (not exposed-pad), with R_thJA = 65 °C/W on ST's 2-layer 2-oz Cu demo board. At 24 V_IN/5 V_OUT/1.5 A, power dissipation is ~28.5 W × (1 − 5/24) ≈ 22.4 W, resulting in ΔT ≈ 1456 °C - impractical without derating. Real-world continuous output is limited to ~0.8 A at 24 V input with adequate copper area and airflow, per thermal simulation data in DS13554 Section 5.