STMicroelectronics LD2985BM35R

Overview

LD2985BM35R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 3.3 V output, 280 mV dropout at 150 mA, 30 µV_rms output noise, and TTL-compatible inhibit control on Pin 3. It operates from –40 °C to 125 °C and is optimized for battery-powered portable electronics requiring ultra-low quiescent current (80 µA at no load) and precise low-noise regulation.

For engineers reviewing the LD2985BM35R datasheet, LD2985BM35R pinout, LD2985BM35R application, or LD2985BM35R equivalent, this page delivers verified electrical specs, SOT23-5L package mapping, real-world use cases in portable devices, and validated alternative regulators with documented functional trade-offs.

Technical Context

The LD2985BM35R uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV at 1 mA, 280 mV at 150 mA) and sub-1 µA shutdown current when INHIBIT is pulled low. Its internal feedback network sets a precise 3.3 V output with ±1.2% tolerance over temperature and load.

It integrates thermal and current limiting, supports external 10 nF bypass capacitor for noise reduction to 30 µV_rms, and accepts input voltages from 2.5 V to 16 V. The INHIBIT pin requires no pull-up and must not float - logic low (<0.15 V) disables regulation; logic high (>2 V) enables operation.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package: 2.95 mm × 1.60 mm footprint, 1.30 mm max height, thermal resistance R_thJA = 255 °C/W, R_thJC = 81 °C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6210B332MR-G and MIC5205-3.3YM5-TR, the LD2985BM35R uniquely combines 3.3 V regulation, sub-1 µA inhibit-off current, and integrated shutdown control in SOT23-5L - making it optimal for space-constrained, battery-sensitive designs requiring coordinated power sequencing.

Availability

LD2985BM35R is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, automotive cabin cameras, and handheld test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985BM35R 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-precision, low-noise LDO portfolio engineered specifically for battery-powered portable electronics where ultra-low dropout, sub-µA shutdown, and 30 µV_rms noise are critical.

FAQ

What is the minimum input voltage required for the LD2985BM35R to regulate 3.3 V at 150 mA?

The LD2985BM35R requires a minimum input voltage of 3.58 V to maintain regulation at 150 mA load, based on its maximum dropout voltage of 280 mV (3.3 V + 0.28 V). At lighter loads, dropout drops to 7 mV, allowing operation down to 3.307 V. Input voltage must remain within the absolute maximum rating of 16 V and minimum operating limit of 2.5 V.

Can the INHIBIT pin be left unconnected?

No - the INHIBIT pin has no internal pull-up or pull-down and must never be left floating. If shutdown control is unused, it must be tied directly to the IN pin to ensure continuous operation. Leaving it open risks unpredictable enable/disable behavior due to noise coupling, potentially causing output instability or intermittent dropout.

What output capacitor value is required for stability with the LD2985BM35R?

For the 3.3 V version, ST specifies a minimum 2.2 µF ceramic capacitor with low ESR placed within 12.7 mm of the OUT pin. Tantalum capacitors may be used but are less preferred due to size and cost. Capacitor tolerance and temperature drift must guarantee ≥2.2 µF across –40 °C to 125 °C to maintain loop stability.

Does the LD2985BM35R support reverse current protection?

Yes - the internal PNP pass transistor lacks an inherent body diode, so no reverse current flows from OUT to IN when V_OUT > V_IN. However, a small reverse leakage (~160 µA) flows through internal feedback resistors to GND. This is not destructive and falls within safe operating limits defined in the datasheet.