STMicroelectronics LDS3985M33R

Overview

LDS3985M33R from STMicroelectronics is a fixed 3.3 V, 300 mA low-dropout (LDO) linear voltage regulator in SOT23-5L package. It delivers ultra-low dropout (150 mV typ. at 300 mA), low quiescent current (85 µA typ. at no load), and low output noise (30 µV_RMS), enabling stable power for noise-sensitive analog and RF circuitry in battery-constrained systems.

For engineers reviewing the LDS3985M33R datasheet, LDS3985M33R pinout, LDS3985M33R application, or LDS3985M33R equivalent, key selection criteria include dropout performance under 300 mA load, shutdown logic compatibility with 1.2 V–1.4 V enable thresholds, thermal behavior up to 125 °C junction, and ceramic capacitor stability with CO ≥ 2.2 µF and CBYP = 33 nF.

Technical Context

The LDS3985M33R employs BiCMOS process technology to achieve simultaneous low dropout and low quiescent current - critical for always-on subsystems. Its internal current and thermal limiting protect against overloads without external components, while the dedicated bypass pin (CBYP) enables sub-100 kHz noise suppression via a 33 nF capacitor.

Logic-controlled inhibit functionality operates with TTL-compatible thresholds (VINH ≤ 0.4 V for OFF, ≥ 1.2 V for ON), and supply voltage rejection reaches 55 dB at 1 kHz - making it suitable for post-regulation filtering of switching converter outputs in mixed-signal SoC power domains.

Key Specifications

Pinout & Package

SOT23-5L package: 5-pin surface-mount, 2.95 mm × 1.60 mm footprint, 0.95 mm pitch, thermally enhanced with exposed pad (not electrically connected). Compatible with standard reflow profiles and automated assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P332MR and NCP1117ST33T3G, the LDS3985M33R uniquely balances ultra-low dropout, sub-100 µA quiescent current, integrated shutdown, and 30 µV_RMS noise - making it optimal for compact, battery-sensitive, and noise-critical designs where SOT23-5L footprint is required.

Availability

LDS3985M33R is available at Aetrix Electronics and suitable for wireless sensor nodes, portable medical devices, industrial PLC I/O modules, and automotive body control units requiring stable component supply across temperature and lifecycle.

Supply support for LDS3985M33R 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 LDS3985 belongs to ST's high-performance analog LDO portfolio, engineered specifically for low-noise, low-power, and automotive-qualified power management in space-constrained embedded systems.

FAQ

What is the minimum input voltage required for stable 3.3 V output at 300 mA?

The LDS3985M33R requires a minimum input voltage of 3.45 V (3.3 V + 150 mV typical dropout) to maintain regulation at full 300 mA load. Below 2.5 V input, the device is not guaranteed to operate - per absolute maximum ratings, VI must be ≥2.5 V for functional operation.

Can the BYPASS pin be left unconnected?

No - the BYPASS pin must be connected to a 33 nF ceramic capacitor to ground. Leaving it floating degrades output noise performance and may cause instability; the capacitor provides critical high-frequency reference decoupling and improves PSRR above 10 kHz.

Is the SOT23-5L package RoHS-compliant and lead-free?

Yes - the LDS3985M33R in SOT23-5L is manufactured per ST's ECOPACK®2 standard, fully RoHS-compliant and lead-free, with halogen-free molding compound and matte tin (Sn) termination on all leads.

Does the LDS3985M33R require an input capacitor?

Yes - a minimum 1 µF X5R/X7R ceramic capacitor must be placed between VI and GND, within 2 mm of the pins. This stabilizes the control loop during line transients and prevents oscillation, especially with long input traces or high-impedance sources.