STMicroelectronics LK112SM28TR

Overview

LK112SM28TR from STMicroelectronics is a low-noise, low-dropout linear voltage regulator with shutdown control, delivering 2.8 V at up to 200 mA output current. It features a maximum dropout voltage of 500 mV at full load, 30 µV_rms output noise (10 Hz–80 kHz), ±2% output voltage tolerance at 25 °C, and operates from input voltages as low as V_OUT + 0.5 V (≥2 V versions). It is used in battery-powered sensor nodes and portable instrumentation requiring stable, ultra-low-quiescent-power regulation.

For engineers reviewing the LK112SM28TR datasheet, LK112SM28TR pinout, LK112SM28TR application, or LK112SM28TR equivalent, key selection criteria include shutdown logic compatibility (TTL/CMOS), thermal performance in SOT23-5L, bypass-capacitor-dependent noise reduction, and internal current/thermal protection behavior under fault conditions.

Technical Context

The LK112SM28TR uses an internal PNP pass transistor to achieve low dropout and supports input voltages from 3.3 V to 14 V (since V_OUT = 2.8 V > 2 V). Its shutdown pin (SHDN) accepts TTL/CMOS logic levels: device enables above 1.8 V and disables below 0.6 V, drawing only 0.1 µA in OFF mode.

Output noise is actively reduced via a dedicated Bypass pin accepting a 0.1 µF capacitor, lowering RMS noise to 30 µV. Internal protection includes thermal shutdown (T_J < 150 °C), short-circuit current limiting (~200 mA), and line/load regulation within 20 mV and 90 mV respectively across full operating range.

Key Specifications

Pinout & Package

The LK112SM28TR is housed in a compact, thermally enhanced SOT23-5L package with exposed die attach flag connected internally to GND for improved power dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS7A2028PDQNR and MCP1703T-2802E/MB, the LK112SM28TR uniquely combines a dedicated bypass pin for guaranteed 30 µV_rms noise, TTL/CMOS-compatible shutdown, and 0.1 µA OFF current - making it optimal for space-constrained, battery-operated analog systems needing both precision and intelligence.

Availability

LK112SM28TR is available at Aetrix Electronics and suitable for wearable health monitors, industrial 4–20 mA transmitters, portable gas detectors, and smart meter analog front-ends requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for LK112SM28TR 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 LK112S series was developed specifically for ultra-low-power, low-noise linear regulation in space-constrained portable and sensor applications - emphasizing minimal quiescent current, integrated protection, and noise-reduction architecture without external complexity.

FAQ

What is the minimum input voltage required for LK112SM28TR to regulate 2.8 V?

The minimum input voltage is V_OUT + 0.5 V = 3.3 V, per the datasheet's operative input range specification for V_OUT > 2 V. At 200 mA load, dropout is guaranteed ≤0.5 V, so 3.3 V input sustains regulation. Below 3.3 V, output collapses linearly with input.

Is a capacitor required on the Bypass pin, and what happens if it is omitted?

Yes - a 0.1 µF ceramic capacitor is mandatory on the Bypass pin to achieve the specified 30 µV_rms output noise. Without it, output noise rises to ~120 µV_rms (typical), degrading performance in precision analog circuits. The regulator remains functional but fails its low-noise design intent.

Can LK112SM28TR drive a 200 mA load continuously in SOT23-5L without overheating?

Yes, but only with adequate PCB copper area. With R_thJA = 255 °C/W and P_D = (3.3 V − 2.8 V) × 0.2 A = 100 mW, junction temperature rise is ~25.5 °C above ambient. In 25 °C ambient, T_J ≈ 50.5 °C - well below the 125 °C max rating. Thermal relief vias to inner ground planes are recommended for sustained 200 mA operation.

Does the shutdown pin require a pull-up resistor, or can it be driven directly from a microcontroller GPIO?

It can be driven directly from a microcontroller GPIO. The SHDN pin draws only 12–35 µA when high (1.8 V), and the logic threshold is defined as ≥1.8 V for ON and ≤0.6 V for OFF. No external pull-up is needed; standard 3.3 V or 1.8 V GPIO outputs meet the voltage and current requirements.