STMicroelectronics L6981C33DR

Overview

L6981C33DR from STMicroelectronics is a synchronous step-down DC-DC converter delivering up to 1.5 A output current with fixed 3.3 V output, 3.5–38 V input range, 20 µA quiescent current (LCM mode), and SO8 package. It operates in low-consumption mode (LCM) for high light-load efficiency and supports industrial 24 V bus power systems, smart meters, and always-on sensor nodes.

For engineers reviewing the L6981C33DR datasheet, L6981C33DR pinout, L6981C33DR application, or L6981C33DR equivalent, key selection criteria include its VIN-compatible enable pin, internal soft-start (1.3 ms), output overvoltage protection (120% VOUT), thermal shutdown (165 °C), and dual-mode light-load operation (LCM vs. LNM).

Technical Context

The L6981C33DR implements peak current mode control with internal slope compensation and an integrated transconductance error amplifier featuring an internal compensation network. Its fixed 3.3 V output is sensed via the VOUT/FB pin using an internal voltage divider (VFB = 0.85 V reference).

It features pulse-by-pulse high-side and valley current sensing for robust overcurrent protection, with peak current limit of 2.0 A (typ.) and valley current limit of 1.85 A (typ.). The EN/CLKIN pin provides VIN-compatible enable functionality and-only in LNM variants-external clock synchronization; L6981C33DR is an LCM variant, so synchronization is not supported.

Key Specifications

Pinout & Package

Package: SO8 (SOIC-8, 150 mil width), surface-mount, RoHS-compliant, with exposed thermal pad (PGND-connected). Thermal resistance R_thJA = 65 °C/W on ST's 2-layer 2-oz Cu demo board.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LMR14015QPWPRQ1 and TPS54202DRCT, the L6981C33DR uniquely combines 38 V input capability, sub-µA shutdown, internal compensation, and LCM mode - making it optimal for cost-sensitive, space-constrained, and battery-backed industrial 24 V systems where design simplicity and ultra-low standby power are mandatory.

Availability

L6981C33DR is available at Aetrix Electronics and suitable for industrial sensor nodes, smart metering systems, and robot cleaner control boards requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for L6981C33DR 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, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L6981 series belongs to ST's high-voltage monolithic DC-DC converter product line, engineered specifically for robust, low-component-count power conversion in 24 V industrial and battery-powered equipment where efficiency, reliability, and ease of use are critical.

FAQ

What is the difference between L6981C33DR and L6981C50DR?

The L6981C33DR delivers a fixed 3.3 V output, while the L6981C50DR provides a fixed 5.0 V output. Both share identical input range (3.5–38 V), 1.5 A current capability, SO8 package, and LCM operation mode. Their internal feedback dividers are trimmed to target 3.3 V or 5.0 V respectively, with matching accuracy (±1.5% at 25 °C) and temperature drift (±0.03%/°C).

Does L6981C33DR support external synchronization?

No. L6981C33DR is an LCM (low-consumption mode) variant, and external clock synchronization via the EN/CLKIN pin is supported exclusively on LNM (low-noise mode) versions such as L6981ADJDR. On L6981C33DR, pin 5 functions solely as a VIN-compatible enable input with 1.2 V threshold and 0.2 V hysteresis.

How does the switch-over feature reduce input current in L6981C33DR?

In fixed-output versions like L6981C33DR, the switch-over feature powers internal circuitry from the VOUT pin instead of VIN when VOUT is present and stable. This reduces total input current draw to IQ_VIN = IQ_OPVIN + (VOUT/VIN) × IQ_VOUT/η, achieving ≤3.5 µA typical operating IQ - significantly lower than adjustable versions that draw full IQ from VIN.

Can L6981C33DR operate with input voltage below 3.5 V?

No. The absolute minimum operating input voltage is 3.5 V per datasheet specifications. Below this, the internal VCC LDO cannot regulate (VCC UVLO falling threshold is 2.15 V), causing device reset. Attempting operation at 3.3 V or lower will result in intermittent or no regulation, and is outside guaranteed operating conditions.