STMicroelectronics LK112M21TR

Overview

LK112M21TR from STMicroelectronics is a low-noise, low-dropout linear voltage regulator with integrated shutdown control and internal PNP pass transistor. It delivers up to 150 mA output current, maintains 350 mV dropout at full load, achieves 30 µVrms output noise (10 Hz–80 kHz) with 0.1 µF bypass capacitor, and operates from input voltages as low as V_OUT + 0.5 V (for V_OUT > 2 V). It is used in battery-powered sensor nodes requiring stable 2.1 V supply with ultra-low quiescent current.

For engineers reviewing the LK112M21TR datasheet, LK112M21TR pinout, LK112M21TR application, or LK112M21TR equivalent, key selection criteria include shutdown logic compatibility (TTL/CMOS), thermal shutdown threshold (150 °C), output voltage accuracy (±2%), noise performance under 60 mA load, and SOT23-5L footprint constraints in space-constrained PCB layouts.

Technical Context

The LK112M21TR employs an internal PNP pass transistor architecture enabling low dropout operation while maintaining stability with minimal external capacitance. Its shutdown function accepts TTL/CMOS-compatible logic levels on the SHDN pin, reducing quiescent current to ≤0.1 µA in OFF mode and ≤250 µA in ON mode at zero load.

Output noise is actively suppressed via a dedicated Bypass pin accepting a 0.1 µF capacitor, lowering RMS noise to 30 µV across 10 Hz–80 kHz. Internal protection includes current limiting, thermal shutdown (trip at ~150 °C), and short-circuit foldback - all implemented without external components.

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, R_thJC = 81 °C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AP2210K-2.1TRG1 and MCP1702T-2102E/MB, the LK112M21TR uniquely combines shutdown control, dedicated noise bypass, and SOT23-5L packaging - making it the sole option among the three for space-constrained, battery-operated systems demanding both low noise and dynamic power gating.

Availability

LK112M21TR is available at Aetrix Electronics and suitable for wearable health monitors, industrial wireless transmitters, portable gas detectors, and smart meter auxiliary power systems requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LK112M21TR 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 devices for industrial, automotive, and consumer markets.

The LK112 series belongs to ST's precision linear regulator product line, engineered specifically for ultra-low-noise, low-quiescent-current applications in battery-powered and space-constrained embedded systems.

FAQ

What is the minimum input voltage required for LK112M21TR to regulate 2.1 V?

The LK112M21TR requires a minimum input voltage of V_OUT + 0.5 V = 2.6 V when regulating 2.1 V, per the datasheet's operative input range specification for V_OUT > 2 V. This 500 mV headroom ensures stable regulation even at 150 mA load, where dropout reaches 350 mV - leaving 150 mV margin for line and load transients.

Can the Bypass pin be left unconnected?

Yes, the Bypass pin may be left floating or tied directly to GND, but doing so forfeits the low-noise benefit: output noise rises from 30 µV_rms to approximately 120 µV_rms. For applications requiring <50 µV_rms noise - such as high-resolution ADC references - a 0.1 µF X7R ceramic capacitor must be placed between Bypass and GND.

Does LK112M21TR require an input capacitor?

The datasheet specifies CI = 1 µF as typical for stability testing, but the LK112M21TR remains stable without an input capacitor due to its internal compensation. However, a 1 µF ceramic input capacitor is strongly recommended to suppress high-frequency noise from upstream switching regulators or battery impedance, especially in noisy industrial environments.

How does thermal shutdown behave during continuous overload?

When output current exceeds the internal current limit or junction temperature reaches ~150 °C, the LK112M21TR enters thermal shutdown and disables regulation - pulling OUT to near-GND. It automatically recovers once junction temperature falls below ~140 °C, enabling hiccup-mode operation that prevents permanent damage without external reset circuitry.