STMicroelectronics LD2981ABU50TR

Overview

LD2981ABU50TR from STMicroelectronics is a 100 mA fixed-output low-dropout linear voltage regulator with 5.0 V output, ultra-low dropout (180 mV typ. at 100 mA), 80 µA typical quiescent current in active mode, and <1 µA shutdown current. It features TTL-compatible inhibit control on pin 3, ±0.75% output voltage tolerance, and 160 µV_RMS output noise-designed for battery-powered portable electronics requiring stable, low-noise local regulation.

For engineers reviewing the LD2981ABU50TR datasheet, LD2981ABU50TR pinout, LD2981ABU50TR application, or LD2981ABU50TR equivalent, key selection criteria include dropout behavior under 100 mA load, inhibit logic thresholds (V_IL ≤ 0.18 V, V_IH ≥ 1.6 V), thermal shutdown at 170 °C, SOT23-5L package compatibility, and ceramic capacitor stability requirements (min. 2.2 µF, low ESR).

Technical Context

The LD2981ABU50TR uses a PNP pass transistor architecture enabling ultra-low dropout voltage-only 7 mV at 1 mA and 180 mV at 100 mA-while maintaining tight line/load regulation (0.014 %/V and ±0.3% over 1–100 mA). Its internal feedback network sets nominal 5.0 V output with ±0.75% initial tolerance and supports operation across –40 to +125 °C junction temperature.

Shutdown is implemented via a dedicated INHIBIT pin (pin 3) with TTL-compatible thresholds and sub-1 µA off-mode current; the pin is not internally pulled up and must never float. The device integrates thermal shutdown (170 °C) and current limiting, and is optimized for ceramic output capacitors ≥2.2 µF with specified ESR range to ensure stability across temperature and load transients.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 1.3 mm × 2.9 mm footprint, 1.45 mm height, with exposed pad for thermal dissipation (not electrically connected). Pin 4 is NC; pin 3 is INHIBIT with no internal pull-up.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700T-5002E/TT and NCP1117ST50T3G, the LD2981ABU50TR uniquely balances ultra-low dropout, precise 5.0 V output, integrated inhibit control, and SOT23-5L compactness - making it optimal for space- and power-constrained portable systems requiring dynamic power management.

Availability

LD2981ABU50TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, automotive cabin electronics, and consumer audio accessories requiring stable component supply with guaranteed long-term availability.

Supply support for LD2981ABU50TR 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-I_Q LDO portfolio, engineered specifically for battery-powered portable devices demanding minimal quiescent current, tight output tolerance, and reliable shutdown control in miniature packages.

FAQ

What is the minimum input voltage required for stable 5.0 V output at 100 mA load?

The LD2981ABU50TR requires a minimum input voltage of 5.18 V (5.0 V + 180 mV typical dropout) to maintain regulation at full 100 mA load. At lower loads, dropout decreases significantly-e.g., only 7 mV at 1 mA-allowing operation from weaker sources such as partially discharged batteries.

Can the INHIBIT pin be left unconnected if shutdown functionality is not needed?

No-the INHIBIT pin has no internal pull-up and must never be left floating. If shutdown is unused, pin 3 must be tied directly to VIN to ensure continuous regulator operation; failure to do so may cause erratic enable/disable behavior or complete output disable.

Which output capacitor specifications are mandatory for stability?

A minimum 2.2 µF ceramic capacitor with ESR < 1 Ω is required for the 5.0 V version. ST specifies this value based on worst-case stability analysis across temperature and load; using lower capacitance or higher ESR risks oscillation, especially during load transients.

Does the LD2981ABU50TR support reverse current protection?

Yes-the internal PNP pass transistor lacks a body diode, preventing reverse current flow from VOUT to VIN. When VOUT exceeds VIN, reverse current is limited to ~160 µA through internal feedback resistors (R1 = 42.6 kΩ, R2 = 51.15 kΩ), eliminating need for external blocking diodes.