STMicroelectronics LD2985BM50R

Overview

LD2985BM50R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator delivering 5.0 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 rail regulator in portable battery-powered systems requiring ultra-low noise and standby power optimization.

For engineers reviewing the LD2985BM50R datasheet, LD2985BM50R pinout, LD2985BM50R application, or LD2985BM50R equivalent, this page provides verified technical context, SOT23-5L package mapping, real-world load/line regulation behavior, thermal performance data, and validated alternative options for 5 V LDO replacement in space-constrained, low-power embedded designs.

Technical Context

The LD2985BM50R uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV at 1 mA, 280 mV at 150 mA) and inherently low reverse current (<160 µA when V_OUT > V_IN). Its inhibit function operates via TTL-compatible input (V_IL ≤ 0.15 V, V_IH ≥ 2 V) on Pin 3, with no internal pull-up-requiring explicit biasing to VI or GND.

Stability relies on external ceramic output capacitors (minimum 1 µF for 5 V output), with ESR sensitivity mitigated by internal compensation. The Bypass (Pin 4) terminal accepts a 10 nF capacitor to ground, reducing broadband output noise to 30 µV_rms (300 Hz–50 kHz), critical for RF and precision analog subsystems.

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 thermal pad not connected internally; standard JEDEC MO-178AC footprint. Pin 1 is marked by dot; top-view orientation follows SC12360 outline.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 5 V LDO regulator applications.

Compared with TPS73550DRVR and MCP1703T-5002E/MB, LD2985BM50R uniquely combines sub-µA inhibit-off current, dedicated noise-reduction bypass pin, and 280 mV dropout-making it optimal for battery-powered systems requiring both aggressive power gating and analog-grade cleanliness without added components.

Availability

LD2985BM50R is available at Aetrix Electronics and suitable for portable medical sensors, automotive body control modules, industrial IoT edge nodes, and smart home hub power management requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD2985BM50R 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-performance analog power management portfolio, engineered specifically for ultra-low-noise, low-quiescent-current regulation in space-constrained portable and automotive electronics.

FAQ

What is the minimum input voltage required for stable 5 V output at 150 mA?

The LD2985BM50R requires a minimum input voltage of 5.28 V to maintain regulation at 150 mA load, based on its 280 mV dropout specification. Below this, output voltage collapses linearly with input; operation below 2.5 V input is prohibited per absolute maximum ratings.

Can the INHIBIT pin be left unconnected?

No. The INHIBIT pin has no internal pull-up or pull-down; leaving it floating risks undefined operation and potential oscillation. When not used, it must be tied directly to the IN pin to ensure permanent enable. A resistor divider is not recommended due to leakage current sensitivity.

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

Yes, a minimum 1 µF ceramic capacitor is mandatory on the IN pin, placed within 12.7 mm and connected to a clean analog ground. X7R or X5R dielectrics are preferred; tantalum or film types are acceptable but less effective for high-frequency decoupling.

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

The BYPASS pin connects an internal noise-reduction circuit to an external 10 nF capacitor, shunting high-frequency reference amplifier noise to ground. Without it, output noise rises to ~120 µV_rms. It is optional only if system noise budget permits higher values; omitting it forfeits the 30 µV_rms specification.