Accurate Proximity Detection in Automotive Applications From Hall Effect Switches

By Charles Kuo, Hall Sensor Product Line Manager

Autonomous vehicles aren’t quite here yet, but they’re getting closer with Advanced Driver Assist Systems (ADAS) such as lane departure warnings and adaptive cruise control. Cars also feature a growing list of technology features to make driving easier, safer, and more comfortable, and ever-more sophisticated onboard computers to manage everything.

To make all this possible, the vehicle also needs to be well-equipped with a range of different sensors. One of the most useful types is the Hall effect sensor, which detects position and movement of any metal part.

A Hall effect sensor measures the potential difference, or voltage, that is produced by a current in a conductor in the presence of a magnetic field. The voltage is proportional to the magnetic field.

Hall effect sensors are often used for current sensing, speed detection, and proximity detection. This can be achieved with one or more permanent magnets mounted on a moving or rotating object, which then affects the voltage produced in a static Hall effect sensor. For example, with two magnets mounted on a wheel or disk, the speed of its rotation can be determined.

Taking this one step further, a Hall effect switch contains a Hall effect sensor, as well as digital circuitry to determine when the magnetic field rises above or drops below a pre-programmed value. The switch has a simple digital output, which reads either one or zero depending on the magnetic field.

To meet the demand for high-sensitivity, automotive-compliant* Hall effect switches, Diodes Incorporated (Diodes) has launched two new families of devices, the AH332xQ and AH352xQ.

The switches provide robust and accurate proximity detection and are suitable for a broad range of contactless applications in vehicles, including seatbelt fastening, door and trunk latching, windshield wipers, and steering-wheel locks.

The AH332xQ is unipolar, which means that it is only activated when the magnetic flux density of correct polarity exceeds the defined operating threshold. The AH352xQ is omnipolar, which means that is activated when the magnetic flux density of either a magnetic south or north pole exceeds the pre-set threshold.

The threshold voltages provide a tight operating window with enough hysteresis for reliable operation, while a low-temperature coefficient ensures the stability of the switching points.

For maximum flexibility in system designs, ten sensitivity options are available for the AH332xQ, allowing a wide range of magnet and distance choices for optimal sensing. The AH352xQ is likewise available in three high-sensitivity options.

Both families are qualified to AEC-Q100 Grade 0 with an extended temperature range of -40ºC to +150ºC, a wide input voltage range of 3V to 28V, and 40V load dump protection. They provide a reliable solution over their entire operating range and ensure robustness with supply-rail reverse blocking with a Zener clamp, and overcurrent limiting with a Zener clamp on the output.

Automotive-compliant - AEC qualified, manufactured in sites certified to IATF 16949 and supporting PPAP documentation.

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