STMicroelectronics STKNX

Overview

STKNX from STMicroelectronics is a KNX TP1-256-certified transceiver IC for twisted-pair building automation networks, integrating dual voltage regulators (3.3 V/5 V linear regulator, 1–12 V adjustable 150 mA buck converter), bus power extraction up to 30 mA, and programmable dI/dt slew rate control - enabling compact, self-powered KNX node designs with microcontroller interface simplicity.

For engineers reviewing the STKNX datasheet, STKNX pinout, STKNX application, or STKNX equivalent, key selection criteria include KNX TP1-256 compliance, integrated dual-regulator architecture, bus current extraction capability, thermal performance in VFQFPN24, and compatibility with standard KNX physical layer timing and impedance requirements.

Technical Context

The STKNX implements a fully compliant KNX TP1-256 bus interface with transmitter, receiver, and impedance modulator blocks - supporting active pulse (35 µs, ~7.5 V drop) and equalization phase (69 µs) timing per the KNX standard, with bus DC voltage detection thresholds referenced to VREF (e.g., KNX_OK rising at 13.5 V relative to VREF).

Its dual-regulator subsystem includes a selectable-output linear regulator (3.3 V/5 V, 20 mA) and a high-efficiency buck converter (1–12 V output, 150 mA, 0.9 V feedback reference, UVLO at 10 V, OTP at 140 °C), both powered from the KNX bus via VDDHV_PD (30 mA max) and configurable via external resistors (RFB1/RFB2) and capacitors (CSS, COUT).

Key Specifications

Pinout & Package

VFQFPN24 package with 24-pin top-side layout and thermally enhanced exposed pad (connected to analog ground). Pin numbering follows standard counter-clockwise sequence from top-left corner (Pin 1 = VDD_REGIN).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar KNX transceiver applications.

Compared with TLE6250G and PCA8574A, STKNX uniquely integrates KNX-compliant transceiver, dual regulators, and 30 mA bus power extraction in one VFQFPN24 package - enabling fully self-contained, space-constrained KNX nodes without external power or bus interface components.

Availability

STKNX is available at Aetrix Electronics and suitable for smart lighting control, HVAC actuation, access control, and energy monitoring gateways requiring stable component supply across industrial building automation programs.

Supply support for STKNX 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 specializing in microcontrollers, power management, and industrial interface solutions, with deep expertise in building automation and KNX ecosystem development.

The STKNX belongs to ST's dedicated KNX transceiver product line, designed specifically to simplify certified, low-power, bus-powered node development for EN 50090-compliant building management systems.

FAQ

What KNX standards does the STKNX comply with?

The STKNX is certified for KNX TP1-256 compliance per EN 50090-2-2, covering full physical layer requirements including active pulse timing (35 µs), equalization phase (69 µs), bus impedance modulation, dI/dt control, and voltage level thresholds. It supports the full 20–32 V DC bus range and meets KNX Class A power consumption limits.

How is the 3.3 V / 5 V linear regulator output selected?

VCCCORE output voltage is selected via the VCC_SEL pin: tie to ground for 3.3 V (typ. 3.3 V, min 3.0 V, max 3.6 V), or tie to VCCCORE for 5 V (typ. 5.0 V, min 4.5 V, max 5.5 V). The internal 6 µA pull-down ensures default 3.3 V if left floating; changing VCC_SEL during operation is not recommended.

Can the STKNX operate without an external microcontroller?

No - the STKNX is a physical layer transceiver only and requires an external microcontroller for protocol handling (KNX stack), message framing, and application logic. It provides only the analog-to-digital and digital-to-analog conversion layer between the KNX bus and MCU GPIOs (KNX_TX, KNX_RX, KNX_OK, VCC_OK).

What is the maximum allowable bus voltage ripple during active transmission?

Per KNX TP1-256 specification and STKNX characterization, the bus voltage ripple during active pulse must remain within ±1.5 V of the nominal DC level (20–32 V) at the R68 node. The STKNX achieves this through its integrated impedance modulator and recommended external components (e.g., 100 nF CPH/CPL, 47 µF CGATE, ≥100 µF CVDDHV).