STMicroelectronics LD2985BM15R

Overview

LD2985BM15R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator with 1.5 V output, ultra-low dropout (7 mV at 1 mA), 80 µA quiescent current at no load, and logic-controlled inhibit function. It operates from −40 °C to 125 °C and delivers low-noise regulation (30 µV_rms) when paired with a 10 nF bypass capacitor-ideal for powering RF sections or precision analog circuitry in portable battery-operated devices.

For engineers reviewing the LD2985BM15R datasheet, LD2985BM15R pinout, LD2985BM15R application, or LD2985BM15R equivalent, this regulator's precise 1.5 V output, sub-1 µA shutdown current, SOT23-5L footprint, and TTL-compatible INHIBIT pin are critical for low-power system partitioning and noise-sensitive power rail design.

Technical Context

The LD2985BM15R uses a PNP pass transistor architecture enabling ultra-low dropout voltage across its full 1–150 mA load range. Its internal feedback network sets a fixed 1.5 V output without external resistors, and the dedicated Bypass pin allows direct connection of a 10 nF capacitor to ground to suppress thermal noise.

Inhibit control is implemented via Pin 3 (INHIBIT), which disables regulation when pulled below 0.15 V (TTL low), reducing total supply current to <1 µA. The device lacks an internal pull-up on INHIBIT, requiring explicit biasing-either to V_IN for always-on operation or to a controlled logic signal for dynamic power gating.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 1.45 mm height, 2.95 mm × 1.60 mm footprint, exposed pad not present. RoHS-compliant, ECOPACK2 certified.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P152MR and ADP160ACBZ-1.5-R7, the LD2985BM15R uniquely combines sub-1 µA shutdown, integrated bypass noise reduction, and TTL-compatible inhibit-all in SOT23-5L-making it optimal for compact, dynamically powered analog subsystems.

Availability

LD2985BM15R is available at Aetrix Electronics and suitable for wireless sensor nodes, portable medical devices, industrial IoT edge controllers, and wearable biometric modules requiring stable component supply across multi-year production cycles.

Supply support for LD2985BM15R 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-efficiency linear regulator product line, engineered specifically for battery-powered and noise-sensitive applications where ultra-low dropout, minimal quiescent current, and logic-controlled power gating are essential.

FAQ

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

The LD2985BM15R requires an input voltage ≥1.78 V at 150 mA load, based on its maximum dropout voltage of 280 mV (typical 280 mV, max 350 mV per datasheet Table 5). At 25 °C and 150 mA, regulation is maintained down to VI = VO + VDROP = 1.5 V + 0.28 V = 1.78 V. Derating is required above 85 °C ambient due to R_thJA = 255 °C/W.

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 unused, it must be tied directly to V_IN to ensure continuous operation. Leaving it unconnected risks erratic enable/disable behavior due to noise coupling, potentially causing output instability or unintended shutdown.

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

Yes-an input capacitor of at least 1 µF is mandatory for stability and transient response. ST recommends X7R ceramic capacitors placed within 12.7 mm (0.5 inch) of the IN pin and returned to a clean analog ground. Tantalum or film capacitors are acceptable alternatives, but ceramic offers superior ESR and reliability for this application.

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 filters reference voltage fluctuations. A 10 nF ceramic capacitor to GND is specified to achieve 30 µV_rms noise; values between 4.7 nF and 22 nF are acceptable per ST application notes, but deviation outside this range may degrade noise performance or stability.