STMicroelectronics LD3985M30R

Overview

LD3985M30R from STMicroelectronics is a 3.0 V, 150 mA ultra-low-dropout linear regulator in SOT23-5L package, featuring 60 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 capacitors as low as 1 µF, and targets power-sensitive battery-operated systems such as mobile phone baseband ICs and RF front-end modules.

For engineers reviewing the LD3985M30R datasheet, LD3985M30R pinout, LD3985M30R application, or LD3985M30R equivalent, key selection criteria include its 85 µA no-load quiescent current, 60 dB PSRR at 1 kHz, guaranteed 150 mA output with thermal/current limiting, and compatibility with low-ESR ceramic bypass capacitors for noise-sensitive analog rails.

Technical Context

The LD3985M30R uses a BiCMOS architecture to achieve ultra-low dropout and low-noise regulation without requiring external compensation. Its internal reference and error amplifier are optimized for stability with 1 µF ceramic output capacitors and a dedicated 10 nF bypass capacitor on the BYPASS pin to suppress high-frequency noise.

Shutdown is controlled via a TTL/CMOS-compatible inhibit input (VINH), with defined logic thresholds (≤0.4 V for OFF, ≥1.2 V for ON) and sub-1.5 µA OFF-mode current. Thermal shutdown activates at 160 °C with 20 °C hysteresis, and internal current limiting caps peak output at 600 mA under short-circuit conditions.

Key Specifications

Pinout & Package

LD3985M30R is housed in a RoHS-compliant, ECOPACK®-qualified SOT23-5L package (1.45 mm × 1.60 mm × 0.95 mm height), optimized for space-constrained PCB layouts and reflow compatibility.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P302MR and MIC5205-3.0YM5, the LD3985M30R delivers superior low-load efficiency (85 µA IQ), lower noise (30 µV_RMS), and integrated shutdown-making it optimal for battery-constrained, noise-sensitive designs where every microamp and microvolt matters.

Availability

LD3985M30R is available at Aetrix Electronics and suitable for mobile baseband power, RF front-end bias, and wearable sensor hub applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LD3985M30R 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 LD3985 belongs to ST's ultra-low-noise, low-quiescent-current LDO family, engineered specifically for battery-powered portable electronics where power efficiency, noise immunity, and small-footprint integration are critical design constraints.

FAQ

What is the minimum output capacitor required for stable operation of LD3985M30R?

The LD3985M30R requires a minimum 1 µF ceramic output capacitor with ESR between 5 mΩ and 5 Ω for guaranteed stability across temperature and load. ST validates performance with X7R dielectrics; using smaller values risks oscillation or degraded transient response, especially under fast load steps.

Can the BYPASS pin be left unconnected?

No - the BYPASS pin must be connected to a 10 nF ceramic capacitor referenced to GND. Leaving it floating degrades PSRR by up to 20 dB and increases output noise beyond the specified 30 µV_RMS, compromising performance in RF and precision analog applications.

Does LD3985M30R support reverse-voltage protection?

No - the LD3985M30R lacks internal reverse-polarity protection. Applying reverse voltage to VI or VO may cause latch-up or permanent damage. External protection (e.g., series Schottky diode) is required if system-level reverse-battery or hot-swap events are possible.

How does thermal shutdown behave during sustained overload?

When junction temperature reaches 160 °C, thermal shutdown disables the pass element and forces VO to drop. After cooldown of ~20 °C (hysteresis), the device automatically recovers. This cycle repeats under continuous overload, preventing permanent damage but causing output voltage ripple - design must ensure adequate heatsinking or current limiting upstream.