STMicroelectronics LK112M55TR

Overview

LK112M55TR from STMicroelectronics is a low-noise, low-dropout linear voltage regulator with integrated shutdown control and 5.5 V fixed output. It delivers up to 150 mA, maintains 350 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 5.5 V bias.

For engineers reviewing the LK112M55TR datasheet, LK112M55TR pinout, LK112M55TR application, or LK112M55TR equivalent, key selection criteria include its SOT23-5L package footprint, TTL/CMOS-compatible SHDN logic interface, internal thermal/current protection, and bypass-capacitor-enabled noise reduction capability.

Technical Context

The LK112M55TR uses an internal PNP pass transistor to achieve low dropout and supports input voltages from 6.0 V (V_OUT + 0.5 V) to 14 V. Its shutdown function reduces quiescent current to ≤0.1 µA, and the Bypass pin accepts a 0.1 µF capacitor to suppress broadband output noise.

Thermal shutdown activates below 150 °C junction temperature, and overcurrent protection limits output to 150 mA under short-circuit conditions. Line regulation is ±20 mV across VI = V_OUT + 1 V to V_OUT + 6 V, and load regulation holds ±30 mV from 1 mA to 60 mA.

Key Specifications

Pinout & Package

Supplied in SOT23-5L package: compact 2.95 mm × 1.60 mm surface-mount outline 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 TPS7A2055PDBVR and MCP1703T-5502E/MB, the LK112M55TR uniquely balances ultra-low noise, logic-controlled shutdown, and sub-400 mV dropout - making it optimal where analog fidelity, dynamic power gating, and minimal input headroom are simultaneously required.

Availability

LK112M55TR is available at Aetrix Electronics and suitable for portable medical sensors, industrial process transmitters, wireless sensor nodes, and test & measurement probes requiring stable component supply with guaranteed long-term manufacturability.

Supply support for LK112M55TR 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, designing and manufacturing analog, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The LK112 series belongs to ST's precision linear regulator product line, engineered specifically for applications demanding low noise, low dropout, and intelligent power control in space- and power-constrained environments.

FAQ

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

The LK112M55TR requires a minimum input voltage of 6.0 V - defined as V_OUT + 0.5 V per datasheet specifications. Below this threshold, regulation fails and output drops linearly with input. This 0.5 V headroom is lower than standard LDOs, enabling use with marginal supplies like partially discharged Li-ion cells.

Can the Bypass pin be left unconnected?

Yes, the Bypass pin may be left floating or tied to GND, but doing so forfeits the low-noise benefit: output noise rises from 30 µV_rms to ~120 µV_rms. For noise-sensitive loads such as precision ADCs or RF synthesizers, a 0.1 µF X7R ceramic capacitor must be placed directly between BYPASS and GND, as specified in Section 4 of the datasheet.

Does the LK112M55TR require an input capacitor?

An input capacitor is not mandatory for stability but is strongly recommended: a 1 µF ceramic capacitor placed close to the IN pin suppresses high-frequency noise from upstream sources and improves transient response. The datasheet specifies CI = 1 µF in all electrical test conditions and typical characteristic plots.

How does thermal shutdown behave under sustained overload?

When junction temperature exceeds ~150 °C, the LK112M55TR disables the pass transistor and halts output. It remains latched off until temperature falls below ~135 °C (typical hysteresis), then automatically resumes regulation. This cycle repeats if overload persists - protecting the device without requiring external reset circuitry.