STMicroelectronics LD2981CM30TR

Overview

LD2981CM30TR from STMicroelectronics is a 100 mA fixed-output low-dropout linear voltage regulator with 3.0 V output, logic-controlled inhibit function, ultra-low dropout (180 mV typ. at 100 mA), and 160 μVRMS output noise. It operates from 2.5 V to 16 V input, supports -40 °C to 125 °C junction temperature, and is designed for battery-powered portable electronics requiring stable low-noise bias.

For engineers reviewing the LD2981CM30TR datasheet, LD2981CM30TR pinout, LD2981CM30TR application, or LD2981CM30TR equivalent, key selection criteria include shutdown quiescent current (<1 μA), dropout voltage vs load, output voltage tolerance (±0.75% for A version), thermal shutdown threshold (170 °C), and compatibility with low-ESR ceramic capacitors.

Technical Context

The LD2981CM30TR uses a PNP pass transistor architecture enabling ultra-low dropout-7 mV typical at 1 mA and 180 mV at 100 mA-while maintaining stability with 2.2 μF ceramic output capacitance. Its inhibit pin (Pin 3) accepts TTL-compatible logic levels (VIH ≥ 1.6 V, VIL ≤ 0.18 V) to enable/disable regulation without external pull-ups.

Internal protection includes current limiting, thermal shutdown at 170 °C, and reverse-current blocking (no body diode between VIN and VOUT). The device achieves 63 dB supply voltage rejection at 1 kHz and delivers ±0.75% initial output accuracy over temperature (–40 °C to 125 °C) in the 'A' grade variant.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, thermally enhanced plastic case with exposed drain pad (Pin 5 = VOUT, Pin 1 = VIN, Pin 2 = GND, Pin 3 = INHIBIT, Pin 4 = NC). Compatible with standard reflow profiles and PCB assembly processes.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700T-3002E/TT and NCP1117ST30T3G, the LD2981CM30TR uniquely combines sub-μA shutdown, 180 mV dropout, and integrated inhibit logic-making it optimal for space-constrained, battery-operated devices demanding both low noise and intelligent power gating.

Availability

LD2981CM30TR is available at Aetrix Electronics and suitable for cellular phone power management, PDA core regulation, digital camera sensor bias, and portable audio DAC supply requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for LD2981CM30TR 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 automotive-grade components.

The LD2981 belongs to ST's ultra-low-quiescent-current LDO family, engineered specifically for portable and battery-powered applications where extended runtime, low noise, and intelligent power control are critical design requirements.

FAQ

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

The LD2981CM30TR requires a minimum input voltage of 3.18 V (3.0 V + 180 mV typical dropout) to maintain regulation at 100 mA. At lower loads, dropout decreases significantly-e.g., 7 mV at 1 mA-allowing operation down to ~3.007 V. Input must remain ≥2.5 V per absolute maximum ratings.

Can the INHIBIT pin be left unconnected?

No-the INHIBIT pin is not internally pulled up or down and must never be left floating. To ensure reliable ON operation, tie Pin 3 directly to VIN. To enable shutdown, drive it to ≤0.18 V (e.g., via microcontroller GPIO). Floating risk causes unpredictable enable/disable behavior and potential instability.

Which output capacitor type and value are mandatory for stability?

A 2.2 μF X5R or X7R ceramic capacitor with ESR ≤ 100 mΩ is required for stability with the 3.0 V version. ST specifies this value based on worst-case loop gain; using smaller capacitance or higher-ESR types (e.g., tantalum) risks oscillation unless compensated with a series resistor per Figure 19 in the datasheet.

Does the LD2981CM30TR support reverse current protection?

Yes-it blocks reverse current flow from VOUT to VIN due to its PNP pass transistor topology (no intrinsic body diode). When VOUT exceeds VIN, only leakage current (~160 μA) flows through internal feedback resistors to GND, preventing backfeed into upstream supplies-a key advantage in multi-rail systems with independent power domains.