STMicroelectronics LK112SM55TR

Overview

LK112SM55TR from STMicroelectronics is a 5.5 V fixed-output, low-noise, low-dropout linear voltage regulator with shutdown control in SOT23-5L package. It delivers up to 200 mA output current, maintains ≤500 mV dropout at full load, achieves 30 µV_rms output noise (10 Hz–80 kHz), and draws only 250 µA quiescent current in ON mode-ideal for battery-powered sensor nodes and portable instrumentation requiring stable, clean power.

For engineers reviewing the LK112SM55TR datasheet, LK112SM55TR pinout, LK112SM55TR application, or LK112SM55TR equivalent, key selection criteria include its 5.5 V output tolerance (±2%), shutdown logic compatibility (TTL/CMOS), thermal shutdown protection (150 °C), internal current limiting, and bypass-capacitor-enabled noise reduction capability.

Technical Context

The LK112SM55TR employs an internal PNP pass transistor to achieve low dropout performance across its operating input range (V_OUT + 0.5 V to 14 V). Its shutdown function is controlled via a dedicated TTL/CMOS-compatible SHDN pin that disables regulation when pulled below 0.6 V, reducing quiescent current to ≤0.1 µA.

Output stability is enhanced by an external 0.1 µF capacitor on the Bypass pin, which reduces integrated output noise to 30 µV_rms. Internal protection includes thermal shutdown (junction limited to <150 °C) and short-circuit current limiting (~200 mA), with line/load regulation specified at ≤40 mV and ≤90 mV respectively.

Key Specifications

Pinout & Package

SOT23-5L surface-mount package with exposed die attach flag for improved 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 TLV70755DBVR and MCP1703T-5502E/MB, the LK112SM55TR offers superior noise performance (30 µV_rms vs ≥40 µV_rms), tighter output tolerance (±2% vs ±3%), and integrated shutdown with sub-µA OFF current-making it the preferred choice for precision, low-power, and space-constrained designs.

Availability

LK112SM55TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial IoT edge nodes, test & measurement probes, and automotive body control modules requiring stable component supply, long-lifecycle support, and consistent parametric performance across production batches.

Supply support for LK112SM55TR 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 LK112S series was developed specifically for ultra-low-noise, low-quiescent-current regulation in space-constrained, battery-operated applications-emphasizing precision, reliability, and ease of integration without external protection components.

FAQ

What is the minimum input voltage required for stable 5.5 V output at 200 mA?

The LK112SM55TR requires a minimum input voltage of 6.0 V (V_OUT + 0.5 V) for full 200 mA load under all operating temperatures. At room temperature and light loads, it may regulate down to 5.65 V due to typical dropout of 0.17 V, but design margin must account for worst-case 0.5 V dropout per datasheet specification.

Can the Bypass pin be left unconnected?

No. Leaving the Bypass pin floating degrades output noise performance: without the 0.1 µF ceramic capacitor, output noise rises significantly above 30 µV_rms. The pin must be decoupled to GND with a 0.1 µF X7R or C0G capacitor placed as close as possible to the device for guaranteed low-noise operation.

Does the LK112SM55TR support reverse polarity or reverse current protection?

No. The device lacks built-in reverse-voltage or reverse-current protection. If input polarity reversal is possible in the system, an external series Schottky diode or ideal diode controller must be added. Reverse current flow from OUT to IN is not blocked and may occur if V_IN falls below V_OUT while the regulator is enabled.

Is the 5.5 V output voltage adjustable via external resistors?

No. The LK112SM55TR is a fixed-output variant with internally trimmed 5.5 V regulation. It does not feature an ADJ pin or feedback network. For adjustable output, ST offers the LK112Sxx family with different fixed voltages, but no pin-compatible adjustable version exists in this series.