STMicroelectronics LD2985AM47R

Overview

LD2985AM47R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 4.7 V output, ultra-low dropout (280 mV at 150 mA), 30 µV_rms output noise, and logic-controlled inhibit shutdown. It operates from −40 °C to 125 °C in SOT23-5L and targets battery-powered portable electronics requiring stable, quiet, low-quiescent-power regulation.

For engineers reviewing the LD2985AM47R datasheet, LD2985AM47R pinout, LD2985AM47R application, or LD2985AM47R equivalent, key selection criteria include dropout voltage at light/heavy load, inhibit logic thresholds (V_IL = 0.15 V, V_IH = 2 V), bypass capacitor dependency for noise reduction, and thermal resistance (R_thJA = 255 °C/W) in compact SOT23-5L layout.

Technical Context

The LD2985AM47R uses a PNP pass transistor architecture enabling sub-10 mV dropout at 1 mA and 280 mV at full 150 mA load. Its inhibit function is TTL-compatible, requiring external pull-up to V_IN when unused and pulling below 0.18 V to achieve <1 µA shutdown current.

Noise performance relies on a dedicated bypass pin (Pin 4) where a 10 nF capacitor to GND reduces 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: 2.95 mm × 1.60 mm × 1.30 mm body, 0.95 mm pitch, exposed pad not electrically connected. Requires minimal PCB area and supports reflow soldering per JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B472MR-G and MIC5205-4.7YM5-TR, the LD2985AM47R uniquely combines TTL-compatible inhibit control, 30 µV_rms noise with minimal 10 nF bypass, and guaranteed −40 °C to 125 °C operation - making it optimal for battery-powered, noise-sensitive, and thermally demanding embedded systems.

Availability

LD2985AM47R is available at Aetrix Electronics and suitable for portable medical sensors, industrial data acquisition modules, smart home motion detectors, and automotive cabin camera modules requiring stable component supply across extended temperature ranges and low-noise regulation.

Supply support for LD2985AM47R 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 LD2985 series belongs to ST's high-performance analog LDO portfolio, engineered specifically for ultra-low-noise, ultra-low-dropout regulation in space- and power-constrained portable and industrial electronics.

FAQ

What is the minimum input voltage required for regulation at 4.7 V output?

The LD2985AM47R maintains regulation as long as input exceeds output by its dropout voltage. At 150 mA load, dropout is 280 mV, so minimum input is 4.98 V. At 1 mA load, dropout drops to 7 mV, allowing regulation from 4.707 V - critical for single-cell Li-ion systems near end-of-discharge.

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 functionality is unused, Pin 3 must be tied directly to the IN pin (V_IN) to ensure reliable ON-state operation across temperature and voltage extremes.

Is an external bypass capacitor mandatory for 30 µV_rms noise performance?

Yes. The 30 µV_rms noise specification is measured with a 10 nF capacitor between Pin 4 (BYPASS) and GND. Without this capacitor, output noise rises to approximately 120 µV_rms, degrading SNR in precision analog circuits like ADC references or RF bias rails.

What output capacitor value is required for stability with 4.7 V output?

For 4.7 V output, ST specifies a minimum 3.3 µF ceramic capacitor (X7R, low-ESR) on the OUT pin. This value ensures phase margin >45° across −40 °C to 125 °C. Using smaller values risks oscillation, especially at high ambient temperatures or heavy load transients.