STMicroelectronics LD2985AM27R

Overview

LD2985AM27R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 2.7 V output, ultra-low dropout (280 mV at 150 mA), 30 µV_rms output noise, and logic-controlled inhibit function on Pin 3. It operates across –40 °C to 125 °C and is used as a local power rail in portable battery-powered systems requiring stable, low-noise supply.

For engineers reviewing the LD2985AM27R datasheet, LD2985AM27R pinout, LD2985AM27R application, or LD2985AM27R equivalent, key selection criteria include dropout voltage at light/heavy load, inhibit logic thresholds, bypass capacitor dependency for noise reduction, thermal resistance (R_thJA = 255 °C/W), and SOT23-5L footprint compatibility.

Technical Context

The LD2985AM27R uses a PNP pass transistor architecture enabling sub-10 mV dropout at 1 mA and 280 mV at full 150 mA load. Its inhibit input (Pin 3) accepts TTL-compatible logic levels (V_IL ≤ 0.15 V, V_IH ≥ 2 V) and reduces quiescent current to <1 µA in shutdown mode.

Noise performance is actively managed via the Bypass pin (Pin 4): a 10 nF capacitor to GND lowers integrated output noise to 30 µV_rms (300 Hz–50 kHz). Internal current and thermal limiting protect against fault conditions without external circuitry.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 1.45 mm height, 2.95 mm × 1.60 mm footprint, exposed pad not present. RoHS-compliant, ECOPACK2 certified.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B272MR-G and ADP125ARHZ-2.7-R7, the LD2985AM27R uniquely combines ultra-low dropout at light load (7 mV), sub-µA inhibit mode, and 30 µV_rms noise in the compact SOT23-5L package-making it optimal for space-constrained, battery-sensitive designs requiring precise low-noise regulation.

Availability

LD2985AM27R is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, smart home audio peripherals, and automotive cabin infotainment systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985AM27R 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, analog chips, and MEMS sensors for industrial, automotive, and consumer markets.

The LD2985 series belongs to ST's high-performance LDO portfolio, engineered specifically for ultra-low-noise, ultra-low-quiescent-current regulation in battery-powered and thermally constrained applications.

FAQ

What is the minimum input voltage required for regulation at 2.7 V output?

The LD2985AM27R maintains regulation down to an input voltage of 2.707 V at 1 mA load (7 mV dropout), and 2.98 V at 150 mA load (280 mV dropout). Below these thresholds, output voltage drops linearly with input. Input must remain ≥2.5 V per absolute maximum ratings.

Can the INHIBIT pin be left unconnected?

No. The INHIBIT pin has no internal pull-up or pull-down and must never be left floating. If shutdown control is not needed, tie Pin 3 directly to the IN pin to ensure continuous operation. Floating INHIBIT may cause erratic enable/disable behavior or increased leakage.

Is an external bypass capacitor mandatory for stable operation?

The 10 nF bypass capacitor on Pin 4 is optional for basic regulation but mandatory to achieve the specified 30 µV_rms output noise. Without it, noise rises to ~100 µV_rms. The capacitor must be X7R ceramic, placed within 2 mm of Pin 4 and GND, with short low-inductance traces.

Does the LD2985AM27R support reverse current protection?

Yes. The internal PNP pass transistor lacks a body diode, preventing reverse current flow from OUT to IN when V_OUT > V_IN. Reverse current through feedback resistors is limited to ~160 µA - sufficient to avoid system-level backfeeding but not intended as primary protection.