STMicroelectronics LD2985BM47R

Overview

LD2985BM47R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 4.7 V nominal output, ultra-low dropout (280 mV at 150 mA), sub-1 µA shutdown quiescent current, and 30 µV_rms output noise enabled by external 10 nF bypass capacitor. It integrates logic-controlled inhibit functionality on Pin 3 (TTL-compatible) and operates across –40 °C to 125 °C for battery-powered portable electronics requiring stable, low-noise local regulation.

For engineers reviewing the LD2985BM47R datasheet, LD2985BM47R pinout, LD2985BM47R application, or LD2985BM47R equivalent, key selection criteria include dropout voltage at light/heavy load, inhibit input threshold compatibility, thermal resistance (R_thJA = 255 °C/W), noise reduction via Bypass pin, and SOT23-5L footprint constraints in space-constrained designs.

Technical Context

The LD2985BM47R employs a PNP pass transistor architecture enabling ultra-low dropout operation - 7 mV at 1 mA and 280 mV at full 150 mA load - while maintaining stability with ceramic output capacitors as low as 2.2 µF (for VO ≤ 3.3 V) or 1 µF (for VO ≥ 3.8 V). Its internal feedback resistors (R1 = 42.6 kΩ, R2 = 51.15 kΩ) set the 4.7 V output and enable reverse-current blocking (no body diode path).

Inhibit control is implemented via a dedicated TTL-compatible input (Pin 3) with V_IL ≤ 0.15 V and V_IH ≥ 2 V; pulling INHIBIT low disables regulation and reduces total supply current to <1 µA. The Bypass pin (Pin 4) accepts a 10 nF capacitor to ground, reducing integrated output noise to 30 µV_rms (300 Hz–50 kHz bandwidth).

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 1.3 mm height, 2.95 mm × 1.60 mm footprint, exposed pad not present, RoHS-compliant ECOPACK2.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B472MR-G and ADP125ARHZ-4.7-R7, the LD2985BM47R uniquely combines sub-1 µA inhibit-off current, dedicated bypass pin for 30 µV_rms noise, and SOT23-5L compactness - making it optimal for space- and noise-constrained battery-powered systems where dynamic power control is essential.

Availability

LD2985BM47R is available at Aetrix Electronics and suitable for portable medical sensors, industrial PLC I/O modules, wearable fitness trackers, and automotive cabin camera systems requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LD2985BM47R 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 high-performance LDO portfolio targeting ultra-low-noise, ultra-low-power portable applications - engineered specifically for battery longevity, thermal efficiency, and signal integrity in compact form factors.

FAQ

What is the minimum input voltage required for regulation at 4.7 V output?

The LD2985BM47R requires an input voltage ≥4.98 V to maintain regulation at full 150 mA load, based on its 280 mV maximum dropout. At lighter loads, input can drop as low as 4.707 V (7 mV dropout at 1 mA). Input must remain ≥2.5 V per absolute maximum ratings, but regulation ceases below VO + VDROP.

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 hard-wired to the input voltage (VI) to ensure continuous regulation. A 10 kΩ resistor to VI is acceptable if driven by high-impedance logic.

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

Yes - a minimum 1 µF ceramic capacitor is required on the IN pin, placed within 12.7 mm of the pin and returned to clean analog ground. X7R or X5R dielectrics are preferred for stable capacitance over temperature and bias; tantalum or film caps are acceptable but less optimal for ESR and size.

How does the Bypass pin reduce output noise, and is the capacitor value flexible?

The Bypass pin connects to an internal noise-reduction circuit that attenuates reference amplifier noise; a 10 nF ceramic capacitor to GND sets the dominant pole and achieves 30 µV_rms. Deviating from 10 nF degrades noise performance - values <5 nF or >22 nF increase integrated noise beyond specification due to phase-margin shift.