Melexis shrinks current sensing footprint with coreless technology

Power electronic designers are constantly faced with the challenge of system size and weight in modern electric vehicles (EVs), resulting in an ongoing demand for smaller and lighter solutions. By eliminating the ferromagnetic concentrator, the gradiometric MLX91235 achieves a significantly smaller footprint than typical current sensor technologies and eliminates hysteresis-related measurement errors. The differential measurement of the magnetic field between two internal sensing elements provides accurate current feedback, as well as ensuring stray field effects are eliminated. Featuring a 500kHz bandwidth and 2μs response time, the sensor is ideally suitable for high-speed applications, such as motor control and converter applications.

Digital architecture and accuracy

The MLX91235’s intelligent digital architecture elevates the sensor's offering, ensuring high measurement accuracy and allowing for the incorporation of several key functions that help to enhance development, calibration, and system integration. When dealing with intrinsic non-linearities, analog architectures often rely on piecewise linear compensations. However, the MLX91235's digital architecture offers the ability to implement more precise and sophisticated compensation, resulting in a more accurate and smoother output. The fully digital-based thermal compensation further ensures that the MLX91235 provides the highest accuracy measurement across its entire working conditions.

Open calibration via SPI

The device’s ‘open’ calibration is configured through a standard serial peripheral interface (SPI) allowing for configuration in situ via any microcontroller unit (MCU). Compared to analog coreless sensors, digital calibration provides a more direct and significantly quicker experience, enabling easy adjustment of elements like digital gain correction.

Over-current detection and temperature monitoring

The built-in 16-bit over-current detection (OCD) allows for asymmetric thresholds and includes two configurable threshold ranges. It features a configurable detection time with a minimum duration of 2μs and an optional debounce strategy. This strategy helps to avoid false positives in harsher electromagnetic compatibility (EMC) environments. Further enhancing its value, the MLX91235 also includes a 10-bit temperature feedback mechanism, enabling accurate measurement of junction temperature that is transmitted through a high-speed SPI output.

Functional safety and self-test

The MLX91235 is ISO 26262 compliant as an ASIL B Safety Element out of Context (SEoOC). Going beyond ASIL B requirements, it also incorporates a sophisticated built-in self-test feature that can be triggered via SPI. This functionality allows the sensor to report critical information like temperature, under-voltage, and mechanical stress. Notably, unlike conventional diagnostics, this functionality encompasses the complete signal chain, up to the application MCU that reads the sensor.

“Melexis has a rich history in current sensing technologies and the coreless MLX91235 is our next step,” said Bruno Boury, Product Line Director at Melexis. He continues: “This sensor brings the optimal mix of in-situ fast calibration including OCD, ISO26262 compliance, and high accuracy owing to the digital core of the sensor. Those features combined with the Melexis customer support are a recipe for success in introducing this new technology into the field.”

Designed to meet the needs of automotive and industrial current sensing applications, the MLX91235 supports PCB and busbar current sensing in systems such as inverters, low-voltage DC/DC converters, chargers, electrically heated catalysts (EHCs), BMSs, smart pyro fuses, and more.

MLX91235 engineering samples and DVK91235 development kits are available now. The product is expected to be fully qualified by mid-2025.