STMicroelectronics LK112SM40TR

Overview

LK112SM40TR from STMicroelectronics is a low-noise, low-dropout linear voltage regulator with shutdown control, designed for power-sensitive analog and mixed-signal circuits. It delivers up to 200 mA output current, maintains ≤500 mV dropout at full load, achieves ±2% output voltage accuracy at 25 °C, and features 30 µV_rms output noise (10 Hz–80 kHz) when using the bypass pin. It is commonly used in portable instrumentation and battery-powered sensor nodes requiring stable, ultra-low-noise bias.

For engineers reviewing the LK112SM40TR datasheet, LK112SM40TR pinout, LK112SM40TR application, or LK112SM40TR equivalent, key selection criteria include its 4.0 V fixed output, SOT23-5L package footprint, 0.1 µA shutdown quiescent current, and internal thermal/overcurrent protection-critical for space-constrained, low-power embedded systems.

Technical Context

The LK112SM40TR integrates an internal PNP pass transistor enabling low-dropout operation across its input range (V_OUT + 0.5 V to 14 V). Its TTL/CMOS-compatible SHDN pin allows logic-level enable/disable control, with ON/OFF transition thresholds at 1.8 V and 0.6 V respectively.

It uses an external 0.1 µF capacitor on the Bypass pin to reduce output noise to 30 µV_rms, and includes internal current limiting and thermal shutdown that activates below 150 °C junction temperature-ensuring robust operation under fault conditions without external circuitry.

Key Specifications

Pinout & Package

Package: SOT23-5L - surface-mount, 5-pin plastic package with exposed die attach flag for enhanced thermal dissipation (R_thJA = 255 °C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P402MR and ADP125ARHZ-4.0-R7, the LK112SM40TR uniquely balances ultra-low shutdown current (0.1 µA), compact SOT23-5L footprint, and integrated bypass-noise reduction-making it optimal for space- and energy-constrained 4.0 V analog subsystems.

Availability

LK112SM40TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial data acquisition modules, wireless sensor nodes, and automotive body electronics requiring stable component supply and long-term manufacturability.

Supply support for LK112SM40TR 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, specializing in microcontrollers, power management, analog ICs, and automotive-grade components.

The LK112S series is part of ST's precision low-noise LDO portfolio, engineered specifically for battery-powered and noise-sensitive applications where minimal dropout, ultra-low quiescent current, and high PSRR are mandatory.

FAQ

What is the minimum input voltage required for stable 4.0 V output?

The LK112SM40TR requires a minimum input voltage of 4.5 V (V_OUT + 0.5 V) for stable regulation at full 200 mA load. At lighter loads, it can operate down to 4.2 V, but dropout increases nonlinearly below 4.5 V-designers should verify margin using the 0.35 V typical dropout at 60 mA from the datasheet.

Can the Bypass pin be left unconnected?

Yes, the Bypass pin may be left floating, but doing so results in higher output noise-approximately 100 µV_rms instead of the specified 30 µV_rms. For noise-critical applications like precision ADCs or RF synthesizers, ST recommends connecting a 0.1 µF ceramic capacitor from Bypass to GND.

Does the LK112SM40TR require external compensation?

No external compensation is required. The device is internally compensated and stable with standard 2.2 µF ceramic output capacitance (X5R/X7R, 6.3 V rated). ST specifies minimum ESR < 100 mΩ and maximum 10 µF total output capacitance for guaranteed stability across temperature and load.

How does thermal shutdown behave during continuous overload?

Under sustained overcurrent or high ambient temperature, the internal thermal limiter reduces output current and cycles the regulator ON/OFF to hold junction temperature below 150 °C. This hysteresis-based protection prevents permanent damage but causes output voltage ripple-designers should size heatsinking or limit average load to avoid repeated cycling.