STMicroelectronics LD2981ABU33TR

Overview

LD2981ABU33TR from STMicroelectronics is a 100 mA fixed-output ultra-low-dropout linear voltage regulator delivering 3.3 V with ±0.75% output tolerance, 160 µV_RMS output noise, and 7 mV typical dropout at 1 mA load. It features logic-controlled inhibit shutdown (TTL-compatible), operates from −40 to 125 °C, and targets low-noise, battery-powered systems requiring precise local regulation.

For engineers reviewing the LD2981ABU33TR datasheet, LD2981ABU33TR pinout, LD2981ABU33TR application, or LD2981ABU33TR equivalent, key selection criteria include dropout performance at light load, sub-1 µA off-mode quiescent current, SOT23-5L package compatibility, and stability with low-ESR ceramic capacitors in space-constrained portable electronics.

Technical Context

The LD2981ABU33TR uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV typ. @ 1 mA) and minimal quiescent current (80 µA typ. @ no load). Its inhibit input (Pin 3) directly controls internal biasing-pulling below 0.18 V disables output and reduces IQ to <1 µA, making it suitable for dynamic power gating.

Stability is achieved with ≥1 µF ceramic output capacitor (2.2 µF recommended for 3.3 V version), leveraging internal compensation optimized for low-ESR capacitors. The device lacks reverse-current protection diode, so output voltage must not exceed input voltage without external clamping.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 1.3 mm × 2.9 mm footprint, exposed pad for thermal dissipation (R_thJA = 255 °C/W), RoHS-compliant and ECOPACK® certified.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-dropout regulator applications.

Compared with TPS7A0533PDBVR and MCP1700-3302E/TO, the LD2981ABU33TR uniquely balances ultra-low dropout (7 mV @ 1 mA), sub-µA shutdown, and SOT23-5L footprint - making it optimal for space-constrained, dynamically powered portable electronics requiring both efficiency and precision.

Availability

LD2981ABU33TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, smart camera modules, and automotive cabin infotainment systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2981ABU33TR 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 silicon solutions for automotive, industrial, and consumer markets since 1987.

The LD2981 series belongs to ST's high-efficiency linear regulator product line, engineered specifically for ultra-low-power, low-noise applications in battery-operated and thermally constrained devices.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 100 mA load?

The LD2981ABU33TR requires input voltage ≥3.48 V at 100 mA load to maintain regulation, based on its maximum dropout voltage of 250 mV (typ. 180 mV). At 1 mA load, input can be as low as 3.307 V due to 7 mV typical dropout. Input must stay within 2.5–16 V absolute ratings.

Can the INHIBIT pin be left unconnected?

No - the INHIBIT pin is not internally pulled up or down and must never be left floating. To ensure reliable operation, tie it directly to VIN if always-on functionality is required, or drive it actively to <0.18 V (logic low) to disable the output and achieve <1 µA quiescent current.

Which output capacitor value and type is mandatory for stability?

A 2.2 µF X5R or X7R ceramic capacitor with ESR <100 mΩ is required for stable operation at 3.3 V output. ST specifies this value based on loop-gain analysis across temperature and load; using smaller capacitance or higher-ESR types (e.g., aluminum electrolytic) risks oscillation and output instability.

Does LD2981ABU33TR provide reverse-current protection?

No - the device uses a PNP pass transistor without an intrinsic body diode, so it blocks reverse current from VOUT to VIN. However, if VOUT exceeds VIN, leakage flows through internal feedback resistors (R1/R2), producing ~160 µA reverse current. External reverse-polarity protection is required if VOUT may be driven independently.