STMicroelectronics LD2981ABM18TR

Overview

LD2981ABM18TR from STMicroelectronics is a 100 mA fixed-output ultra-low-dropout linear voltage regulator with logic-controlled inhibit function, delivering 3.0 V ±0.75% output voltage, 0.17 V typical dropout at 100 mA, and 80 μA typical quiescent current in active mode. It operates across –40 to +125 °C and targets low-noise, battery-powered systems requiring precise local regulation and standby power control.

For engineers reviewing the LD2981ABM18TR datasheet, LD2981ABM18TR pinout, LD2981ABM18TR application, or LD2981ABM18TR equivalent, key selection criteria include its SOT23-5L package compatibility, TTL-compatible INHIBIT pin (logic low <0.18 V disables output), 160 μVRMS output noise, and guaranteed 100 mA output current with internal thermal/current limiting.

Technical Context

The LD2981ABM18TR uses a PNP pass transistor architecture enabling ultra-low dropout-just 7 mV at 1 mA and 180–250 mV at 100 mA-while maintaining stability with low-ESR ceramic capacitors ≥2.2 μF. Its inhibit input (Pin 3) directly controls the pass element via TTL-level logic without internal pull-up, requiring explicit biasing to VI or GND.

It integrates internal current limiting, thermal shutdown at 170 °C, and reverse-current protection (no body diode), eliminating external blocking diodes. The device achieves 63 dB supply voltage rejection at 1 kHz and maintains ±0.75% initial output tolerance over temperature and load variations up to 100 mA.

Key Specifications

Pinout & Package

SOT23-5L (5-pin small-outline transistor) package: compact surface-mount footprint (1.45 mm height, 2.9 mm × 1.6 mm body), thermally enhanced with exposed drain pad connected to VIN internally-requires proper PCB copper pour for thermal management.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700-3002E/TO and NCP1117ST30T3G, the LD2981ABM18TR uniquely combines sub-μA shutdown, integrated inhibit logic, and ultra-low dropout in a space-constrained SOT23-5L-making it optimal for intermittent-duty, battery-critical designs where external enable circuitry adds cost and complexity.

Availability

LD2981ABM18TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial PLC I/O modules, automotive body control units, and wearable fitness trackers requiring stable component supply with full production lifecycle support.

Supply support for LD2981ABM18TR 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 microcontrollers, power management ICs, sensors, and analog devices for industrial, automotive, and consumer markets.

The LD2981 belongs to ST's ultra-low-IQ LDO family, engineered specifically for energy-constrained applications demanding nanoscale shutdown current, precise voltage accuracy, and robust operation across extended temperature ranges.

FAQ

What is the minimum input voltage required for stable 3.0 V output at 100 mA load?

The LD2981ABM18TR requires a minimum input voltage of 3.18 V to maintain regulation at 100 mA, based on its maximum dropout voltage of 250 mV (typ. 180 mV) at that load. Below this, output voltage collapses linearly with input-no brown-out detection or hysteresis is provided.

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

No-the INHIBIT pin has no internal pull-up and must never be left floating. When shutdown is unused, it must be hard-wired to VIN to ensure continuous operation; leaving it open risks erratic enable/disable behavior due to noise coupling or leakage currents.

Which output capacitor ESR range ensures stability for the 3.0 V version in SOT23-5L?

For the LD2981ABM18TR (3.0 V variant), stability is guaranteed with a 2.2 μF ceramic capacitor having ESR between 10 mΩ and 300 mΩ, per Figure 19 ("Worst case: lowest output version") in the datasheet-capacitors outside this range may cause oscillation or poor transient response.

Does the LD2981ABM18TR provide reverse-voltage protection on the input pin?

No-it lacks reverse-input protection. Applying negative voltage to VIN relative to GND exceeds the absolute maximum rating of –0.3 V and can damage the IC. External series diode or TVS clamp is required if reverse polarity exposure is possible in the system design.