STMicroelectronics LD3985M25R

Overview

LD3985M25R from STMicroelectronics is a 2.5 V fixed-output, ultra-low-dropout linear regulator (LDO) in SOT23-5L package, delivering up to 150 mA with 60 mV typical dropout at full load, 30 µV_RMS output noise (10 Hz–100 kHz), and 60 dB PSRR at 1 kHz. It features logic-controlled shutdown, operates from 2.5 V to 6 V input, and is optimized for battery-powered mobile phones and wireless systems requiring stable low-noise bias.

For engineers reviewing the LD3985M25R datasheet, LD3985M25R pinout, LD3985M25R application, or LD3985M25R equivalent, key selection criteria include guaranteed 150 mA output current, sub-1 µA shutdown current, ceramic capacitor compatibility (≥1 µF, ≤5 Ω ESR), fast 200 µs turn-on time, and thermal/overcurrent protection - all validated across –40 °C to +125 °C junction temperature.

Technical Context

The LD3985M25R uses a BiCMOS architecture to achieve ultra-low quiescent current (85 µA typ. at no load) while maintaining high PSRR (60 dB @ 1 kHz) and low noise performance. Its internal reference and error amplifier are designed for stability with low-ESR ceramic capacitors, eliminating need for tantalum or electrolytic types.

Shutdown is controlled via VINH pin with precise thresholds (ON ≥1.2 V, OFF ≤0.4 V), and the BYPASS pin accepts a 10 nF capacitor to suppress high-frequency noise. Dropout behavior is linear down to 0.4 mV at 1 mA, enabling operation near battery end-of-life voltages.

Key Specifications

Pinout & Package

LD3985M25R is housed in a compact, surface-mount SOT23-5L package (2.95 mm × 1.60 mm × 1.45 mm), RoHS-compliant and ECOPACK® certified. The 5-pin layout supports minimal board area and standard reflow assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P252MR and MIC5205-2.5YM5, LD3985M25R delivers superior dropout performance (60 mV vs. ≥120 mV), integrated BYPASS functionality for enhanced noise control, and higher PSRR - making it the optimal choice for battery-constrained, noise-critical applications demanding extended runtime and signal integrity.

Availability

LD3985M25R is available at Aetrix Electronics and suitable for mobile phone baseband power, wireless sensor node regulation, and portable medical monitor biasing requiring stable component supply across long production cycles.

Supply support for LD3985M25R 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 runtime, noise immunity, and small-footprint power integrity are critical design constraints.

FAQ

What is the minimum input voltage required for LD3985M25R to maintain regulation?

The LD3985M25R requires a minimum input voltage of 2.5 V to operate, but to sustain 2.5 V output under 150 mA load, the input must be ≥2.56 V due to its 60 mV typical dropout. At lighter loads (e.g., 1 mA), dropout drops to 0.4 mV, allowing regulation from as low as 2.5004 V - enabling deep battery discharge utilization in Li-ion systems.

Can LD3985M25R be used without the BYPASS capacitor?

Yes, LD3985M25R functions without the 10 nF BYPASS capacitor, but output noise increases from 30 µV_RMS to ~55 µV_RMS, and PSRR degrades by 10–15 dB above 100 kHz. The BYPASS pin is optional for basic applications but mandatory for RF, precision ADC, or low-noise analog circuits per ST's recommended design practice.

Is the shutdown function of LD3985M25R compatible with open-drain GPIOs?

No - VINH is a CMOS-compatible input requiring active drive to ≥1.2 V for ON and ≤0.4 V for OFF. An open-drain GPIO must be pulled up to ≥1.2 V via external resistor (e.g., 100 kΩ to VI) to ensure valid logic high; direct connection without pull-up risks undefined state due to input leakage (<1 nA) and floating threshold sensitivity.

What output capacitor ESR range ensures stability for LD3985M25R?

LD3985M25R is stable with output capacitors having ESR between 5 mΩ and 5000 mΩ (5 Ω), covering standard X7R/X5R ceramics (typically 5–20 mΩ) and some polymer types. ST explicitly validates stability down to 5 mΩ, eliminating need for ESR-added resistors or damping networks required by older LDO architectures.