STMicroelectronics LD2985AM15R

Overview

LD2985AM15R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 1.5 V output, ultra-low dropout (280 mV at 150 mA), 30 µV_rms output noise, and TTL-compatible inhibit control on Pin 3. It operates across –40 °C to 125 °C and delivers stable regulation in battery-powered portable electronics requiring low quiescent current and high PSRR.

For engineers reviewing the LD2985AM15R datasheet, LD2985AM15R pinout, LD2985AM15R application, or LD2985AM15R equivalent, this page provides verified electrical parameters, SOT23-5L package mapping, real-world use cases in power-sensitive embedded systems, and validated alternative regulators for design continuity.

Technical Context

The LD2985AM15R uses a PNP pass transistor architecture enabling ultra-low dropout voltage - as low as 7 mV at 1 mA load - and supports logic-controlled shutdown via an active-low INHIBIT input that reduces quiescent current to <1 µA in sleep mode. Its internal feedback network sets a precise 1.5 V output without external resistors.

Stability is ensured with ceramic output capacitors (minimum 2.2 µF for 1.5 V output), and noise performance is enhanced by a dedicated Bypass pin accepting a 10 nF capacitor to ground, reducing output noise to 30 µV_rms (300 Hz–50 kHz). Thermal protection and current limiting are fully integrated.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package: 2.9 mm × 1.6 mm footprint, 1.3 mm max height, thermal resistance R_thJA = 255 °C/W, designed for compact PCB layouts with minimal thermal vias.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B152MR-G and RT9193-15GB, the LD2985AM15R uniquely balances sub-µA shutdown, 7 mV ultra-low dropout at light loads, and a dedicated bypass pin - making it optimal for space-constrained, battery-critical designs requiring both precision analog supply and intelligent power management.

Availability

LD2985AM15R is available at Aetrix Electronics and suitable for wearable health sensors, industrial IoT edge nodes, portable medical devices, and automotive cabin modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985AM15R 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 analog components for industrial, automotive, and consumer markets.

The LD2985 series belongs to ST's high-performance LDO portfolio targeting ultra-low-noise, ultra-low-I_Q applications in portable and battery-powered systems where efficiency, precision, and reliability are non-negotiable.

FAQ

What is the minimum input voltage required for regulation at full 150 mA load?

The LD2985AM15R requires input voltage ≥1.78 V to maintain 1.5 V output at 150 mA, based on its 280 mV maximum dropout specification. Below this, output voltage collapses linearly with input; operation below 2.5 V input is permitted but must respect the 280 mV headroom margin for regulation.

Can the INHIBIT pin be left floating, or does it require a pull-up resistor?

The INHIBIT pin must never be left floating - it has no internal pull-up or pull-down. When not actively driven, it must be tied directly to the IN pin to ensure continuous operation. Leaving it unconnected risks erratic enable/disable behavior due to noise coupling and violates the absolute maximum rating for VINH.

Is a bypass capacitor mandatory on the BYPASS pin to achieve 30 µV_rms noise performance?

Yes - the 30 µV_rms noise figure is measured with a 10 nF ceramic capacitor connected between Pin 4 (BYPASS) and GND. Without this capacitor, output noise rises significantly (typical 120–150 µV_rms). The capacitor must be placed adjacent to the pin with short, low-inductance traces to ground.

Does the LD2985AM15R support reverse current protection when V_OUT > V_IN?

Yes - the internal PNP pass transistor lacks a body diode, so no forward conduction occurs from OUT to IN. However, a small reverse current (~160 µA) flows from OUT to GND through internal feedback resistors when V_REV is applied; this is specified and safe, but external reverse-blocking diodes are unnecessary.