STMicroelectronics LD2985AM36R

Overview

LD2985AM36R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 3.3 V output, TTL-compatible inhibit control (Pin 3), 280 mV dropout at 150 mA, 30 µV_rms output noise, and operation from –40 °C to 125 °C in SOT23-5L package. It serves as a local power rail regulator in battery-powered portable electronics requiring ultra-low quiescent current and low-noise supply.

For engineers reviewing the LD2985AM36R datasheet, LD2985AM36R pinout, LD2985AM36R application, or LD2985AM36R equivalent, key selection criteria include dropout voltage under load, inhibit logic thresholds, bypass capacitor dependency for noise reduction, thermal resistance (R_thJA = 255 °C/W), and ceramic capacitor stability requirements for 3.3 V output.

Technical Context

The LD2985AM36R employs a PNP pass transistor architecture enabling ultra-low dropout-7 mV at 1 mA and 280 mV at 150 mA-while maintaining stable regulation across –40 °C to 125 °C junction temperature. Its internal feedback network sets nominal 3.3 V output with ±1.2% tolerance over full load and temperature range.

Inhibit functionality is implemented via a dedicated TTL-compatible input (Pin 3) that disables the regulator when pulled below 0.15 V, reducing quiescent current to <1 µA. The Bypass pin (Pin 4) requires a 10 nF capacitor to GND to achieve specified 30 µV_rms noise performance; without it, noise rises significantly.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package (2.95 mm × 1.60 mm × 1.30 mm height), RoHS-compliant, ECOPACK2 qualified, with exposed pad not connected internally.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B332MR-G and ADP125ARHZ-3.3-R7, the LD2985AM36R uniquely delivers sub-µA shutdown, dedicated bypass pin for deterministic 30 µV_rms noise, and guaranteed 280 mV dropout at full 150 mA-making it optimal for space-constrained, ultra-low-power portable systems.

Availability

LD2985AM36R is available at Aetrix Electronics and suitable for portable medical sensors, industrial wireless transceivers, and automotive cabin controllers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985AM36R 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 power delivery in battery-critical portable electronics and harsh-environment embedded systems.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 150 mA load?

The LD2985AM36R requires input voltage ≥3.58 V (3.3 V + 280 mV dropout) for stable regulation at full 150 mA load. Below this, output voltage collapses linearly with input. At lighter loads (e.g., 1 mA), input can be as low as 3.307 V due to 7 mV dropout. Input must stay within absolute maximum rating of 16 V.

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

No-the INHIBIT pin must never be left floating. When shutdown is unused, it must be tied directly to the IN pin (VI) to ensure reliable ON-state operation. Floating the pin risks unintended disable due to noise coupling, causing intermittent output dropout and system reset.

Is a bypass capacitor mandatory for achieving 30 µV_rms output noise?

Yes-a 10 nF ceramic capacitor between the Bypass pin (Pin 4) and GND is mandatory to achieve the specified 30 µV_rms noise. Without it, output noise increases to approximately 100 µV_rms. The capacitor must be placed within 2 mm of Pin 4 and GND with short, low-inductance traces.

What output capacitor value and type are required for stability at 3.3 V output?

For 3.3 V output, a minimum 2.2 µF X7R ceramic capacitor with low ESR (<100 mΩ) is required on the OUT pin. It must be placed within 12.7 mm of the pin and connected to clean analog ground. Tantalum capacitors may work but are discouraged due to size, cost, and ESR drift over temperature.