Fully integrated inductive switch enables small module designs

Melexis has revealed its Induxis switch, the MLX92442. Contactless, magnet-free, and strayfield immune, this monolithic solution directly detects conductive targets. It allows small module designs with lowered component count for improved safety and electrification: high voltage interlocks, charging flaps, seatbelts, hood/trunk, gear tooth sensing, or brake-by-wire applications.

For traditional safety automotive latches and switches, ranging from door and boot/trunk handles to seatbelts and brake light switches, the standard design employs a mechanical contact or magnetic switch, like a push button, reed switch, or hall effect sensor. But for such a solution to operate, the safety target’s design must be modified, to include a magnet plus holder or a physical protrusion to actuate a button. With the company’s revolutionary induction solution, this is no longer the case. Its technology instead actively senses the actual safety target, such as a seat belt buckle or door latch, directly without a magnet or button actuator, provided it is conductive.

This shift in position-sensing technology comes with many benefits. With no moving mechanisms or additional parts, reliability, and safety are improved with the direct sensing operation not tied to parts affixed to the safety element that could become damaged or displaced. Furthermore, the solution helps to reduce the BOM and the inductive contactless operation is inherently more reliable than mechanical solutions which wear over time, as well as being immune to magnetic disturbance.

Central to the switch is its heavily integrated and miniaturised standard packaging. Compared to other inductive solutions, the company's design innovates by fully integrating the coils and interface within the chip, removing the necessity for engineers to develop bulky PCB and coil solutions for their application.

The solution is provided in through-hole VK packaging or surface-mount SOIC packaging. In either case, the supporting BOM is reduced from three to two elements (target + IC/coils) compared to existing solutions, and this, combined with the foregoing magnets, helps to produce a more sustainable and safer design than existing sensors on the market.

Ensuring continued and reliable operation, the switch also includes reverse supply voltage, under-voltage, and thermal protection, and an advanced integrated self-diagnostic function with a dedicated safe mode.

Besides reducing the BOM component count, this inductive solution helps to streamline development time. Both factory and end-of-line programming are supported, and the smart switch/latch operation is established by simply defining the applications’ shape and motion. In contrast to Hall effect solutions, magnetic simulation is not necessary, resulting in saved development time (next to BOM savings).

In terms of assembly design, the standard packaging and lack of magnets plus holder provides for simpler system integration. It streamlines the supply chain, with fewer elements helping to decrease prototyping and production assembly time. This factor also assists to maintain mechanical tolerances in assemblies, as only the inductive sensor and conductive safety element need to be considered within air gaps up to 1.5mm.

With industry standard two or three wire interfaces, a wide operating voltage of 3.5V to 18V, a working temperature window of -40C to 150C and ISO26262 ASIL A compliance, the device’s design considerations are minimal. Furthermore, for safety-critical applications requiring heterogeneous redundancy, the inductive technology provides a highly reliable option with minimal design requirements that can operate next to the Hall effect and mechanical solutions.

“With this new technology, our engineering teams have redefined end-position sensing, delivering a wide range of benefits,” said Minko Daskalov, product manager at Melexis. “Induxis is there to enable the next step in electrification and safety, with battery and hydrogen technologies for both the grid or EVs. The MLX92442 ticks all the right boxes”

The switch is currently in pre-production with engineering B-samples and evaluation kits available.