STMicroelectronics LD2985BM28R

Overview

LD2985BM28R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator delivering 2.8 V with 280 mV dropout at 150 mA, 30 µV_rms output noise (with 10 nF bypass capacitor), and logic-controlled inhibit shutdown reducing quiescent current to <1 µA. It operates across –40 °C to 125 °C and targets battery-powered portable electronics requiring ultra-low noise and standby power efficiency.

For engineers reviewing the LD2985BM28R datasheet, LD2985BM28R pinout, LD2985BM28R application, or LD2985BM28R equivalent, key selection criteria include dropout performance at light load, inhibit input logic thresholds (V_IL = 0.15 V, V_IH = 2 V), thermal resistance (R_thJA = 255 °C/W), SOT23-5L package constraints, and bypass-capacitor–dependent noise reduction.

Technical Context

The LD2985BM28R uses a PNP pass transistor architecture enabling ultra-low dropout-7 mV at 1 mA and 280 mV at 150 mA-while maintaining stability with ceramic output capacitors as low as 2.2 µF. Its internal feedback resistors (42.6 kΩ/51.15 kΩ) set the 2.8 V output and enable reverse-current blocking when V_OUT > V_IN.

Inhibit control is TTL-compatible: pulling Pin 3 (INHIBIT) below 0.18 V disables regulation and reduces supply current to <1 µA; the pin is not internally pulled up and must never float. The dedicated Bypass (Pin 4) terminal accepts a 10 nF capacitor to ground to suppress thermal noise to 30 µV_rms over 300 Hz–50 kHz.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package (2.95 mm × 1.60 mm × 1.30 mm height), RoHS-compliant and ECOPACK® certified, optimized for space-constrained portable PCB layouts with exposed pad thermal path.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B282MR-G and BD70522GUL, the LD2985BM28R uniquely balances ultra-low dropout at microamp loads, dedicated noise-reduction pin, and industry-standard SOT23-5L footprint-making it optimal for legacy-compatible, battery-life–critical portable designs where board space and thermal budget are fixed.

Availability

LD2985BM28R is available at Aetrix Electronics and suitable for smartphone baseband power, wearable sensor hubs, digital camera image sensor bias, and industrial handheld terminals requiring stable component supply across long production lifecycles.

Supply support for LD2985BM28R 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 precision low-dropout regulator product line, engineered specifically for ultra-low-noise, low-power portable electronics where battery longevity and signal integrity are primary design constraints.

FAQ

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

The LD2985BM28R requires an input voltage of at least 3.08 V to maintain 2.8 V output at 150 mA, based on its 280 mV maximum dropout voltage specification. Below this, output voltage collapses linearly with input; operation below 2.5 V input is outside absolute maximum ratings and risks functional failure.

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

No-the INHIBIT pin must never be left floating. When unused, it must be tied directly to the IN pin to ensure the regulator remains enabled. Floating the pin risks erratic enable/disable behavior due to noise coupling, potentially causing system reset or power sequencing faults.

Is an input capacitor mandatory, and what type is recommended?

Yes-a minimum 1 µF ceramic capacitor is mandatory between IN and GND, placed within 12.7 mm of the IN pin. X7R or better dielectric is recommended; tantalum or film types are acceptable but less optimal for ESR and size. Omitting it risks instability and line-transient overshoot exceeding 100 mV.

How does the BYPASS pin reduce output noise, and is it optional?

The BYPASS pin connects a 10 nF capacitor to GND to shunt internal bandgap reference noise, lowering integrated output noise from ~120 µV_rms to 30 µV_rms. It is optional only if noise specifications permit higher values; omitting it degrades noise performance by 4× and may violate RF/analog subsystem requirements.