STMicroelectronics LDS3985PU33R

Overview

LDS3985PU33R from STMicroelectronics is a fixed 3.3 V, 300 mA low-dropout (LDO) linear voltage regulator in DFN6 (3 × 3 mm) package, featuring 150 mV typical dropout at full load, 30 µV_RMS output noise (10 Hz–100 kHz), and logic-controlled shutdown. It operates from 2.5 V to 6 V input, supports ceramic output capacitors down to 2.2 µF, and targets battery-powered systems requiring ultra-low quiescent current (85 µA typ. at no load).

For engineers reviewing the LDS3985PU33R datasheet, LDS3985PU33R pinout, LDS3985PU33R application, or LDS3985PU33R equivalent, key selection criteria include dropout performance under 300 mA load, thermal shutdown threshold (160 °C), SVR (55 dB @ 1 kHz), and compatibility with low-ESR ceramic capacitors in space-constrained portable designs.

Technical Context

The LDS3985PU33R uses a BiCMOS architecture to achieve ultra-low dropout and quiescent current simultaneously. Its internal reference and error amplifier drive a PMOS pass transistor, enabling stable regulation without external compensation and supporting fast turn-on (240 µs) with 33 nF bypass capacitor.

Shutdown is controlled via VINH pin with TTL-compatible thresholds (logic high ≥1.4 V, logic low ≤0.4 V); the pin is not internally biased and must be actively driven. Thermal protection activates at 160 °C with ~20 °C hysteresis, and short-circuit current is internally limited to 600 mA.

Key Specifications

Pinout & Package

DFN6 (3 × 3 mm) package with exposed thermal pad (EP) on underside for enhanced heat dissipation; RoHS-compliant, ECOPACK®2 qualified.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P332MR and NCP114AMX330TBG, the LDS3985PU33R delivers superior noise performance (30 µV_RMS vs >50 µV_RMS) and higher SVR, making it optimal for RF/analog signal chains where power integrity is critical.

Availability

LDS3985PU33R is available at Aetrix Electronics and suitable for mobile terminals, wearable health monitors, industrial IoT nodes, and automotive body control modules requiring stable component supply with guaranteed long-term availability.

Supply support for LDS3985PU33R 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 LDS3985 belongs to ST's high-performance LDO family targeting ultra-low-noise, low-quiescent-current regulation in battery-powered and thermally constrained applications - emphasizing reliability, small-footprint packaging, and automotive qualification options.

FAQ

What is the minimum output capacitor value required for stability?

The LDS3985PU33R is stable with ceramic output capacitors ranging from 2.2 µF to 22 µF and ESR between 5 mΩ and 5000 mΩ. A 2.2 µF X7R ceramic capacitor with ≤100 mΩ ESR is sufficient for most applications and meets the datasheet's minimum requirement for stability across temperature and load.

Can the BYPASS pin be left unconnected?

No - the BYPASS pin must be connected to a 33 nF capacitor (typically C0G/NP0) referenced to GND. Leaving it floating degrades high-frequency PSRR and increases output noise; omitting the capacitor reduces SVR by up to 15 dB at 10 kHz and compromises turn-on transient response.

Is thermal derating required for continuous 300 mA operation in DFN6 package?

Yes - at ambient temperatures above 65 °C, output current must be derated due to thermal resistance (R_thJA = 55 °C/W). With 160 °C thermal shutdown, maximum continuous 300 mA load is supported up to ~85 °C ambient assuming adequate PCB copper area (≥200 mm² 2-oz thermal pad).

Does the LDS3985PU33R support reverse polarity or reverse current protection?

No - the device lacks integrated reverse-voltage or reverse-current blocking. If input can fall below output (e.g., during hot-swap or battery swap), an external Schottky diode or ideal diode controller is required to prevent backfeed through the pass transistor and potential damage to upstream sources.