STMicroelectronics LD2981CM18TR

Overview

LD2981CM18TR from STMicroelectronics is a 1.8 V fixed-output, 50 mA ultra-low-dropout linear regulator in SOT23-5L package, featuring 7 mV typical dropout at 1 mA load, 80 µA quiescent current in active mode, and <1 µA shutdown current. It integrates logic-controlled inhibit functionality (TTL-compatible), internal thermal/current limiting, and stable operation with low-ESR ceramic capacitors - ideal for battery-powered microcontroller core rails in portable IoT sensors.

For engineers reviewing the LD2981CM18TR datasheet, LD2981CM18TR pinout, LD2981CM18TR application, or LD2981CM18TR equivalent, key selection criteria include its sub-10 mV dropout at light load, 160 µVRMS output noise, ±0.5% output voltage tolerance (C version), -40 to 125 °C operating range, and SOT23-5L footprint compatibility with space-constrained PCB layouts.

Technical Context

The LD2981CM18TR employs a PNP pass transistor architecture enabling ultra-low dropout performance without requiring high-side drive circuitry. Its inhibit control pin (Pin 3) directly interfaces with digital logic to enable/disable regulation, with defined VIH/VIL thresholds (1.3–1.6 V high, ≤0.18 V low) and negligible input current (±1 µA).

Stability is achieved using only low-ESR ceramic output capacitors (≥3.3 µF for 1.8 V version), eliminating need for tantalum or electrolytic types. The device's fast transient response (load step: 1→100 mA) and 63 dB supply rejection at 1 kHz support noise-sensitive analog and RF subsystems.

Key Specifications

Pinout & Package

SOT23-5L: 2.95 mm × 1.60 mm × 1.30 mm body, 0.95 mm pitch, exposed pad not present. RoHS-compliant, ECOPACK2 qualified.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LDO regulator applications.

Compared with AP2210K-18W5 and MCP1700T-1802E/TT, the LD2981CM18TR uniquely delivers sub-10 mV dropout at microamp loads and integrated TTL inhibit - making it optimal for energy-harvesting and long-life battery systems where every millivolt and microamp matters.

Availability

LD2981CM18TR is available at Aetrix Electronics and suitable for wearable health monitors, industrial wireless transmitters, automotive cabin modules, and smart home motion detectors requiring stable component supply with guaranteed long-term availability.

Supply support for LD2981CM18TR 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 LD2980/LD2981 series targets ultra-low-power, space-constrained applications - specifically engineered to replace legacy LDOs in battery-operated devices where dropout voltage, quiescent current, and ceramic-capacitor compatibility are critical design constraints.

FAQ

What is the minimum input voltage required for regulation at 1.8 V output?

The LD2981CM18TR maintains regulation as long as input voltage exceeds output voltage plus dropout. At 1 mA load, typical dropout is 7 mV, so minimum VIN is 1.807 V. At 50 mA, dropout rises to 120–150 mV, requiring VIN ≥ 1.92–1.95 V. Full temperature range derating must be applied per Table 6.

Can the INHIBIT pin be left floating?

No - the INHIBIT pin has no internal pull-up or pull-down. Leaving it floating risks undefined output state and potential oscillation. If shutdown control is unused, tie INHIBIT directly to VIN to ensure continuous regulation. A resistor divider is unnecessary and adds leakage risk.

Which output capacitor value and type are mandatory for stability?

For the 1.8 V version, ST specifies ≥3.3 µF low-ESR ceramic (X7R or X5R) with ESR ≤1 Ω. Tantalum capacitors are not recommended due to higher ESR and aging effects. Capacitor must be placed within 12.7 mm of VOUT and GND pins, with short, low-inductance traces.

Does the LD2981CM18TR provide 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), protecting upstream power sources.