STMicroelectronics LD2985BM18R

Overview

LD2985BM18R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 1.8 V output, 280 mV dropout at 150 mA, 30 µV_rms output noise, and logic-controlled inhibit shutdown. It operates from −40 °C to 125 °C and uses a 10 nF bypass capacitor to achieve ultra-low noise-ideal for powering RF-sensitive analog sections in portable battery-powered devices.

For engineers reviewing the LD2985BM18R datasheet, LD2985BM18R pinout, LD2985BM18R application, or LD2985BM18R equivalent, key selection criteria include its sub-1 µA shutdown current, TTL-compatible INHIBIT pin behavior, SOT23-5L thermal resistance (R_thJA = 255 °C/W), and ceramic-capacitor stability requirements for 1.8 V output.

Technical Context

The LD2985BM18R employs a PNP pass transistor architecture enabling ultra-low dropout (7 mV at 1 mA, 280 mV at 150 mA) and minimal quiescent current (80 µA no-load, <1 µA in inhibit mode). Its internal feedback network sets a precise 1.8 V output with ±1.2% tolerance over temperature and load.

It integrates thermal and current limiting, supports external bypass capacitance on the dedicated Bypass pin to reduce output noise to 30 µV_rms, and accepts input voltages from 2.5 V to 16 V. The INHIBIT pin (Pin 3) is not internally pulled up and requires explicit logic-level control for reliable enable/disable operation.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package: 2.95 mm × 1.60 mm footprint, 1.45 mm height, 0.95 mm pin pitch, thermally enhanced die pad (exposed cathode not present).

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P182MR and AP2204K-18, the LD2985BM18R uniquely delivers sub-300 mV dropout, sub-1 µA inhibit current, and guaranteed 30 µV_rms noise with integrated bypass-making it optimal for compact, battery-critical, noise-sensitive designs where all three parameters are simultaneously required.

Availability

LD2985BM18R is available at Aetrix Electronics and suitable for portable medical sensors, wearable biometric monitors, industrial IoT edge nodes, and RF module power management requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985BM18R 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 linear regulator product line, engineered specifically for ultra-low-noise, ultra-low-quiescent-current operation in space-constrained, battery-powered applications demanding precision voltage regulation.

FAQ

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

The LD2985BM18R requires an input voltage ≥2.08 V to maintain 1.8 V output at 150 mA, based on its 280 mV maximum dropout voltage. Below this threshold, the output collapses linearly with input; operation below 2.5 V is permitted but must account for worst-case dropout across temperature and unit variation.

Can the INHIBIT pin be left floating?

No-the INHIBIT pin is not internally pulled up or down and must never be left floating. If unused, it must be hard-connected to the IN pin to ensure continuous operation. Floating causes undefined output state and potential oscillation due to noise coupling into the high-impedance control node.

Is a bypass capacitor mandatory for achieving 30 µV_rms noise?

Yes-30 µV_rms output noise is only achievable when a 10 nF ceramic capacitor is connected between the Bypass pin and GND. Without this capacitor, output noise increases significantly (typical >100 µV_rms), compromising performance in precision analog or RF applications.

What output capacitor value is required for stability at 1.8 V?

A minimum 2.2 µF X7R ceramic capacitor is required on the OUT pin for stability with the 1.8 V version. This value is specified in Section 6.3 of the datasheet and accounts for ESR and temperature drift; using smaller values risks oscillation unless compensated with a series resistor.