STMicroelectronics LD2981ABM25TR

Overview

LD2981ABM25TR from STMicroelectronics is a 2.5V fixed-output, 100mA ultra-low-dropout linear voltage regulator in SOT-23-5L package, featuring 0.17V typical dropout at 100mA, 80µA typical quiescent current in active mode, and <1µA shutdown current. It integrates logic-controlled inhibit functionality (TTL-compatible), ±0.75% output voltage tolerance, and operates across –40°C to +125°C for battery-powered portable electronics.

For engineers reviewing the LD2981ABM25TR datasheet, LD2981ABM25TR pinout, LD2981ABM25TR application, or LD2981ABM25TR equivalent, key selection criteria include dropout voltage at light/heavy load, inhibit threshold compatibility with host logic, ceramic capacitor stability requirements (min. 2.2µF, low ESR), and thermal performance in SOT-23-5L under 100mA continuous load.

Technical Context

The LD2981ABM25TR uses a PNP pass transistor architecture enabling ultra-low dropout (7mV typ. at 1mA; 180mV typ. at 100mA) and minimal quiescent current variation across load. Its inhibit input (Pin 3) directly controls internal biasing-no pull-up required-and asserts shutdown when driven below 0.18V.

Stability is guaranteed with low-ESR ceramic capacitors (2.2µF min. for 2.5V version), and internal current/thermal limiting protects against overload and fault conditions. Output noise is specified at 160µVRMS (300Hz–50kHz), supporting noise-sensitive analog rails in mixed-signal systems.

Key Specifications

Pinout & Package

SOT-23-5L package: 2.9mm × 1.6mm × 1.3mm body, surface-mount, lead-free (ECOPACK®), rated for 255°C/W junction-to-ambient thermal resistance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700-2502E/TO and NCP1117DT25RKG, the LD2981ABM25TR uniquely combines sub-µA shutdown, ±0.75% accuracy, and integrated inhibit in SOT-23-5L - making it optimal for space-constrained, battery-sensitive designs requiring precise, controllable 2.5V regulation.

Availability

LD2981ABM25TR is available at Aetrix Electronics and suitable for portable medical sensors, wearable health monitors, industrial IoT edge nodes, and automotive body control modules requiring stable component supply with full traceability and long-term lifecycle support.

Supply support for LD2981ABM25TR 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 ultra-low-power linear regulator product line, engineered specifically for battery-operated portable electronics demanding minimal quiescent current, tight output tolerance, and logic-controllable shutdown in miniature packages.

FAQ

What is the minimum input voltage required for regulation at 100mA load?

The LD2981ABM25TR requires a minimum input voltage of 2.68V (2.5V + 0.18V dropout) to maintain regulation at 100mA load and 25°C. At –40°C to +125°C, worst-case dropout rises to 375mV, so minimum input must be ≥2.875V across full temperature range. Input below this causes output collapse.

Can the INHIBIT pin be left unconnected?

No - the INHIBIT pin has no internal pull-up or pull-down and must never be left floating. If shutdown control is unused, tie Pin 3 directly to VIN to ensure continuous operation. Floating INHIBIT may cause erratic enable/disable behavior due to noise coupling, risking unintended power cycling.

Which output capacitor value and type are mandatory for stability?

For the 2.5V version, a minimum 2.2µF X7R ceramic capacitor with ESR ≤1Ω is required at the output. ST specifies this value based on loop stability testing across temperature and load; using smaller capacitance or higher-ESR types (e.g., standard Y5V) risks oscillation and output ripple amplification.

Does the LD2981ABM25TR support reverse current protection?

Yes - the internal PNP pass transistor lacks a body diode, preventing reverse current flow from VOUT to VIN when output voltage exceeds input. Reverse current is limited to ~160µA via internal feedback resistors (R1=42.6kΩ, R2=51.15kΩ), eliminating need for external blocking diodes in backup-supply configurations.