STMicroelectronics LD2981CM50TR

Overview

LD2981CM50TR from STMicroelectronics is a 100 mA fixed-output ultra-low-dropout linear regulator with logic-controlled inhibit function, delivering 5.0 V ±0.75% over −40 to 125 °C, 160 μVRMS output noise, and 180 mV typical dropout at 100 mA load. It serves as a local power rail supervisor in battery-powered portable electronics requiring low quiescent current and fast transient response.

For engineers reviewing the LD2981CM50TR datasheet, LD2981CM50TR pinout, LD2981CM50TR application, or LD2981CM50TR equivalent, key selection criteria include its 0.17 V dropout at 100 mA, <1 μA off-mode current, TTL-compatible inhibit input (V_IL = 0.18 V), SOT23-5L package footprint, and ceramic-capacitor stability requirements.

Technical Context

The LD2981CM50TR employs a PNP pass transistor architecture enabling ultra-low dropout voltage and minimal quiescent current across load and temperature. Its internal feedback network uses precision trimmed resistors (R1 = 42.6 kΩ, R2 = 51.15 kΩ) to achieve ±0.75% output tolerance and supports reverse-current blocking via absence of intrinsic body diode.

Inhibit control is implemented as a dedicated TTL-compatible digital input (Pin 3) that disables regulation when pulled below 0.18 V, reducing IQ to <1 μA without requiring external pull-up. The device operates stably with ≥2.2 μF ceramic output capacitor and exhibits 63 dB supply rejection at 1 kHz.

Key Specifications

Pinout & Package

LD2981CM50TR is housed in a RoHS-compliant SOT23-5L package (1.3 mm × 2.9 mm × 1.15 mm), optimized for high-density portable PCB layouts and reflow compatibility.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output LDO applications.

Compared with MCP1700T-5002E/TT and NCP1117ST50T3G, LD2981CM50TR uniquely balances ultra-low dropout (180 mV), sub-μA shutdown, and integrated inhibit control in a 5-pin SOT23 footprint-making it optimal for compact, battery-sensitive designs requiring per-rail power management.

Availability

LD2981CM50TR is available at Aetrix Electronics and suitable for smartphone baseband power, digital camera sensor bias, portable medical monitor displays, and industrial handheld scanner logic rails requiring stable component supply across automotive-grade temperature ranges and long production lifecycles.

Supply support for LD2981CM50TR 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The LD2981 series belongs to ST's ultra-low-quiescent-current LDO portfolio, engineered specifically for battery-powered portable electronics demanding nanoscale shutdown current, tight output tolerance, and ceramic-capacitor compatibility.

FAQ

What is the minimum input voltage required for LD2981CM50TR to maintain 5.0 V output at 100 mA load?

The typical dropout voltage is 180 mV at 100 mA, so the minimum input voltage is 5.0 V + 0.18 V = 5.18 V. At worst-case conditions (−40 to 125 °C), dropout rises to 375 mV, requiring VI ≥ 5.375 V to guarantee regulation. Input must stay within absolute maximum rating of 16 V.

Can LD2981CM50TR operate without an external output capacitor?

No. The device requires a minimum 2.2 μF ceramic output capacitor with appropriate ESR to ensure loop stability across temperature and load. Omitting it causes oscillation or erratic regulation. ST specifies this value for 5.0 V versions; lower-output variants require larger capacitance.

Is the INHIBIT pin internally pulled up, and what happens if left floating?

No-INHIBIT has no internal pull-up and must never be left floating. An unconnected pin may drift into indeterminate logic state, causing unpredictable ON/OFF behavior. When unused, tie it directly to VIN to force permanent enable; for controlled shutdown, drive with a logic signal meeting V_IL ≤ 0.18 V and V_IH ≥ 1.6 V.

Does LD2981CM50TR support reverse current flow from VOUT to VIN?

No. The internal PNP pass transistor lacks an inherent body diode, preventing reverse current conduction. If VOUT exceeds VIN, only leakage through internal feedback resistors flows to GND (typ. 160 μA), eliminating risk of backfeeding upstream supplies or damaging source converters.