STMicroelectronics LD2985BM33R

Overview

LD2985BM33R from STMicroelectronics is a 150 mA fixed-output low-dropout linear voltage regulator delivering 3.3 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 operates across –40 °C to 125 °C and targets battery-powered portable electronics requiring ultra-low noise and standby power efficiency.

For engineers reviewing the LD2985BM33R datasheet, LD2985BM33R pinout, LD2985BM33R application, or LD2985BM33R equivalent, this page provides verified electrical parameters, SOT23-5L package mapping, inhibit control behavior, thermal performance data, and real-world use cases in handheld and imaging devices.

Technical Context

The LD2985BM33R uses a PNP pass transistor architecture enabling ultra-low dropout (7 mV at 1 mA) and minimal quiescent current (80 µA at no load). Its inhibit input (Pin 3) accepts TTL-compatible logic levels (V_IL ≤ 0.15 V, V_IH ≥ 2 V) and disables regulation without internal pull-up, requiring external biasing when unused.

Output noise is actively suppressed via dedicated Bypass pin (Pin 4), where a 10 nF capacitor to GND reduces broadband noise to 30 µV_rms (300 Hz–50 kHz). Internal current and thermal limiting protect against fault conditions, and reverse-current blocking prevents output-to-input conduction during back-driving.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package (2.95 mm × 1.60 mm × 1.30 mm height) with exposed pad for thermal enhancement; RoHS-compliant and ECOPACK® certified.

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/MB, the LD2985BM33R uniquely combines sub-1 µA shutdown, 30 µV_rms noise via bypass pin, and 280 mV dropout-making it optimal for space-constrained, battery-operated analog-digital hybrid systems.

Availability

LD2985BM33R is available at Aetrix Electronics and suitable for portable imaging devices, wearable health monitors, industrial handheld terminals, and smart home sensor hubs requiring stable component supply across extended product lifecycles.

Supply support for LD2985BM33R 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 chips for industrial, automotive, and consumer markets.

The LD2985 series belongs to ST's high-performance LDO portfolio targeting ultra-low-noise, low-power portable electronics; it emphasizes dropout minimization, shutdown efficiency, and noise suppression for battery-sensitive applications.

FAQ

What is the minimum input voltage required for regulation at 3.3 V output?

The LD2985BM33R maintains regulation down to an input voltage of 3.58 V under full 150 mA load, based on its 280 mV dropout specification. At lighter loads, input can drop as low as 3.307 V (7 mV dropout at 1 mA), enabling compatibility with partially discharged Li-ion cells and low-headroom power architectures.

Can the INHIBIT pin be left unconnected?

No-the INHIBIT pin has no internal pull-up and must never be left floating. If shutdown control is not needed, it must be tied directly to the IN pin to ensure continuous regulation. Floating the pin risks unpredictable enable/disable behavior and potential output instability due to noise coupling.

Is an external capacitor required on the Bypass pin?

Yes-a 10 nF capacitor between Bypass (Pin 4) and GND is mandatory to achieve the specified 30 µV_rms output noise. Without it, noise rises to approximately 80–100 µV_rms. The capacitor must be placed adjacent to the pin with short, low-inductance traces to ground for effective high-frequency reference decoupling.

Does the LD2985BM33R support reverse-current protection?

Yes-it blocks reverse current flow from OUT to IN due to its PNP pass transistor topology lacking an intrinsic body diode. When output voltage exceeds input, reverse current is limited to ~160 µA through internal feedback resistors, preventing backfeed into upstream supplies during hot-swap or partial-system power-down events.