STMicroelectronics LD2981CM33TR

Overview

LD2981CM33TR from STMicroelectronics is a 100 mA fixed-output ultra-low-dropout linear voltage regulator with logic-controlled shutdown, delivering 3.3 V ±0.75% over −40 to 125 °C, featuring 160 μVRMS output noise and 7 mV typical dropout at 1 mA load. It serves as a local power rail regulator in battery-powered portable electronics requiring low quiescent current and fast transient response.

For engineers reviewing the LD2981CM33TR datasheet, LD2981CM33TR pinout, LD2981CM33TR application, or LD2981CM33TR equivalent, key selection criteria include shutdown current (<1 μA), dropout voltage at light/heavy load, output voltage tolerance across temperature, and compatibility with low-ESR ceramic capacitors in SOT23-5L packaging.

Technical Context

The LD2981CM33TR uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV typ. at 1 mA) and sub-1 μA off-mode current. Its inhibit input (pin 3) accepts TTL-compatible logic levels (VIH ≥1.6 V, VIL ≤0.18 V) to enable/disable regulation without external pull-up.

Stability is optimized for ceramic output capacitors ≥2.2 μF (for 3.3 V version) with ESR <1 Ω; internal current and thermal limiting protect against overload and junction temperatures exceeding 170 °C.

Key Specifications

Pinout & Package

LD2981CM33TR is housed in a RoHS-compliant SOT23-5L package (2.9 × 1.6 × 1.3 mm), optimized for space-constrained portable designs and compatible with standard reflow profiles.

Key Features

Applications

Equivalent & Alternatives

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

Compared with AP2112K-3.3TRG1 and MCP1700T-3302E/TT, LD2981CM33TR uniquely combines sub-μA shutdown, <250 mV dropout at full 100 mA, and integrated TTL-compatible inhibit - making it optimal for portable systems requiring coordinated power sequencing and battery longevity.

Availability

LD2981CM33TR is available at Aetrix Electronics and suitable for cellular handset power rails, PDA core regulation, digital camera sensor biasing, and portable audio DAC supply requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2981CM33TR 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, specializing in power management, microcontrollers, and analog ICs for automotive, industrial, and consumer markets.

The LD2981 series belongs to ST's ultra-low-dropout linear regulator product line, engineered specifically for battery-powered portable devices demanding minimal quiescent current, tight output tolerance, and robust thermal performance in miniature packages.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 100 mA load?

The LD2981CM33TR requires a minimum input voltage of 3.48 V (3.3 V + 180 mV typical dropout) to maintain regulation at 100 mA. At lower loads, dropout drops to 7 mV - enabling operation down to 3.307 V at 1 mA. Input must remain ≥2.5 V per absolute maximum ratings.

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

No - the INHIBIT pin has no internal pull-up and must not be left floating. When shutdown is unused, tie pin 3 directly to VIN to ensure continuous regulation. Floating the pin risks unpredictable enable/disable behavior and potential output instability.

Which output capacitor values and types ensure stability for the 3.3 V version?

For the LD2981CM33TR, use ≥2.2 μF X5R or X7R ceramic capacitors with ESR <1 Ω. Tantalum capacitors may work but increase cost and size; aluminum electrolytics are unstable. Place the capacitor within 12.7 mm of VOUT and GND pins, using a solid analog ground plane.

Does the LD2981CM33TR 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 flows only through internal feedback resistors (typ. 160 μA), eliminating need for external blocking diodes in backup-power or hot-swap configurations.