STMicroelectronics LD2985BM36R

Overview

LD2985BM36R 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 local regulation.

For engineers reviewing the LD2985BM36R datasheet, LD2985BM36R pinout, LD2985BM36R application, or LD2985BM36R equivalent, this page delivers verified electrical specs, SOT23-5L package layout, real-world use cases in power-constrained systems, and validated alternative regulators with documented functional trade-offs.

Technical Context

The LD2985BM36R uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV at 1 mA), while its internal feedback network maintains ±1.5% output accuracy over temperature and load. The inhibit input (Pin 3) directly controls the pass element gate via TTL-level logic, achieving sub-1 µA shutdown current without external pull-up.

Its bypass pin (Pin 4) accepts a 10 nF capacitor to ground, reducing broadband thermal noise to 30 µV_rms (300 Hz–50 kHz). Stability is guaranteed with ≥2.2 µF ceramic output capacitance and ESR < 100 mΩ - no external compensation required.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package (2.95 mm × 1.60 mm × 1.30 mm height), RoHS-compliant, ECOPACK2 qualified.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS7A0533PDBVR and MCP1700T-3302E/TT, the LD2985BM36R uniquely combines sub-1 µA shutdown, 30 µV_rms noise via integrated bypass, and 280 mV dropout - making it optimal for space-constrained, battery-operated systems demanding both efficiency and signal integrity.

Availability

LD2985BM36R is available at Aetrix Electronics and suitable for portable communication devices, wearable health monitors, industrial sensor nodes, and automotive body control modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985BM36R 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 high-precision analog power management portfolio, engineered specifically for ultra-low-noise, low-quiescent-current regulation in portable and battery-powered systems where thermal and electrical efficiency are critical.

FAQ

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

The LD2985BM36R requires an input voltage ≥3.58 V to maintain regulation at 150 mA due to its 280 mV dropout specification. At lighter loads (e.g., 1 mA), input can be as low as 3.307 V. Operation below these thresholds causes output collapse and unregulated behavior.

Can the INHIBIT pin be left floating?

No - the INHIBIT pin has no internal pull-up or pull-down. Leaving it floating risks undefined output state and potential oscillation. When not actively controlled, it must be tied directly to IN to ensure continuous operation, or to GND to force shutdown.

Is an external bypass capacitor mandatory for low-noise operation?

Yes - the 10 nF ceramic capacitor between BYPASS (Pin 4) and GND is required to achieve the specified 30 µV_rms output noise. Without it, noise rises to ~120 µV_rms, degrading performance in precision analog circuits like ADC references or RF bias rails.

What output capacitor value and type are recommended for stability?

ST specifies ≥2.2 µF X7R ceramic with ESR < 100 mΩ for 3.3 V output versions. Tantalum capacitors may be used but require careful ESR validation; aluminum electrolytics are not recommended due to high ESR and temperature drift.