STMicroelectronics LD2985AM33R

Overview

LD2985AM33R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator delivering 3.3 V with 280 mV dropout at 150 mA load, 30 µV_rms output noise (with 10 nF bypass capacitor), and logic-controlled inhibit shutdown reducing quiescent current to <1 µA. It serves as a local power supply in portable battery-powered systems requiring ultra-low noise and standby efficiency.

For engineers reviewing the LD2985AM33R datasheet, LD2985AM33R pinout, LD2985AM33R application, or LD2985AM33R equivalent, key selection criteria include dropout voltage at light/heavy loads, inhibit input logic thresholds (V_IL = 0.15 V, V_IH = 2 V), thermal resistance (R_thJA = 255 °C/W), output capacitor stability requirements (2.2 µF ceramic min for 3.3 V), and SOT23-5L package footprint compatibility.

Technical Context

The LD2985AM33R 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 a precise 3.3 V output (±1.5% over full load/temperature range) without external resistors.

Inhibit control on Pin 3 enables TTL-compatible active-low shutdown, decoupling output from input while limiting reverse current to 160 µA. The dedicated Bypass pin (Pin 4) accepts a 10 nF capacitor to ground, reducing integrated output noise to 30 µV_rms (300 Hz–50 kHz) via internal noise-canceling circuitry.

Key Specifications

Pinout & Package

SOT23-5L is a 5-pin, surface-mount plastic package (2.95 mm × 1.60 mm × 1.30 mm height) with exposed pad for thermal enhancement; JEDEC MO-178AC compliant and RoHS/ECOPACK2 certified.

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 MIC5205-3.3YM5, the LD2985AM33R uniquely combines sub-µA inhibit shutdown, 30 µV_rms noise, and active-low TTL-compatible control in a 150 mA SOT23-5L package - making it optimal for space-constrained, battery-sensitive designs requiring seamless integration with existing low-active logic domains.

Availability

LD2985AM33R is available at Aetrix Electronics and suitable for portable medical sensors, wireless IoT edge nodes, industrial HMI displays, and automotive cabin controllers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985AM33R 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 precision low-noise LDO portfolio, engineered specifically for battery-powered portable electronics where ultra-low dropout, nanoscale quiescent current, and integrated noise filtering are mandatory for analog and RF subsystem integrity.

FAQ

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

The LD2985AM33R requires a minimum input voltage of 3.58 V to maintain regulation at 150 mA load, based on its 280 mV maximum dropout voltage specification. At lighter loads (e.g., 1 mA), input can be as low as 3.307 V due to 7 mV typical dropout. Input below VO + VDROP risks output collapse and unregulated behavior.

Can the BYPASS pin be left unconnected?

No - leaving the BYPASS pin floating degrades output noise performance from 30 µV_rms to >100 µV_rms. A 10 nF ceramic capacitor must be placed directly between Pin 4 (BYPASS) and Pin 2 (GND) with minimal trace length. This capacitor forms part of the internal noise-reduction network and is not optional for low-noise applications.

Does the LD2985AM33R require an external pull-up on the INHIBIT pin?

No - the INHIBIT pin has no internal pull-up. If not actively driven, it must be tied to V_IN (Pin 1) to ensure the regulator remains enabled. Floating the pin risks undefined state, intermittent shutdown, or increased leakage due to noise coupling; ST explicitly warns against leaving it unconnected.

What output capacitor value is required for stability at 3.3 V output?

A minimum 2.2 µF X7R ceramic capacitor with low ESR (<100 mΩ) is required on the OUT pin for stability at 3.3 V output. ST specifies this value based on loop-gain analysis; using less capacitance risks oscillation unless a series resistor is added. The capacitor must be placed within 12.7 mm of Pin 5 and connected to a clean analog ground plane.