Shrinking current sensing footprint with coreless technology

Melexis has unveiled the MLX91235, a new current sensor that eradicates the necessity for a ferromagnetic core. The device expands its portfolio, allowing larger currents to be measured through external primary conductors like PCB traces and busbars. It supports automotive and alternative mobility applications like inverters, BMSs and low-voltage DC-DC converters.

Power electronic designers continually face the challenge of system size and weight in modern EVs, resulting in an ongoing demand for smaller and lighter solutions. By eradicating the ferromagnetic concentrator, the gradiometric device attains a notably smaller footprint than typical current sensor technologies and stops hysteresis-related measurement errors. The differential magnetic field measurement between two internal sensing elements supplies accurate current feedback and eradicates stray field effects. Featuring a 500kHz bandwidth and 2μs response time, the sensor is ideal for high-speed applications, such as motor control and converter applications.

The device's intelligent digital architecture elevates the sensor's offering, ensuring high measurement accuracy and incorporating several key functions that help to improve development, calibration, and system integration. Analog architectures often rely on piecewise linear compensations when dealing with intrinsic non-linearities. However, the device's digital architecture allows more precise and sophisticated compensation, resulting in a more accurate and smoother output. The fully digital-based thermal compensation further ensures it provides the highest accuracy measurement across its working conditions.

The device's 'open' calibration is configured through a standard SPI, allowing for configuration in situ via any MCU. Compared to analog coreless sensors, digital calibration supplies a more direct and significantly quicker experience, enabling easy adjustment of elements like digital gain correction.

The built-in 16-bit over-current detection (OCD) allows for asymmetric thresholds and includes two configurable threshold ranges. It provides a configurable detection time with a minimum duration of 2μs and an optional debounce strategy. This strategy helps to avoid false positives in harsher 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.

The device 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 enables 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 continued: "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, EHCs, BMSs, smart pyro fuses, and more.

Engineering samples and DVK91235 development kits are available now.