Magnetic sensors get smarter for IoT-connected systems

September 08, 2017 // By Graham Prophet
Silicon Labs has added a magnetic sensor portfolio offering power efficiency, sensitivity, flexible I2C configuration, and built-in tamper detection and temperature sensing. The Si72xx portfolio is presented as the most advanced, feature-rich magnetic sensors available, outperforming reed switches and traditional Hall-effect devices in a range of open/close and position-sensing applications.

The sensors provide solid-state reliability for white goods, flow meters, cordless power tools, wheel and dial-type controls for consumer electronics, industrial alarms, motor controls and door/window security applications. The sensors are AEC-Q100-qualified for automotive applications and designed to withstand harsh industrial environments.

 

They solve, Silicon Labs asserts, several tradeoffs in selecting the right magnetic sensing solution for power- and cost-sensitive applications. Reed switches consume very little power but are bulky and unreliable. While Hall-effect sensors offer solid-state reliability, they are more power hungry and conventionally have few of the programmable capabilities and advanced features offered by other modern sensor types used in IoT applications. Silabs says it has achieved the power efficiency of reed switches with the reliability of Hall-effect sensors, while adding more advanced features, higher sensitivity and configurability.

 

Operating below 100 nA (sleep current) and less than 400 nA (averaged) for a 5 Hz sampling rate, Si72xx sensors can help designs achieve multiyear and decade-long battery lifetimes, even when powered by very small batteries. Sensitivity is <1.1 mT Bop, ith <30 µT RMS noise, <0.1% linearity on 20 mT/200 mT ranges, enabling developers to reduce the size of magnetics in their designs by 50 to 80% or extend sensing range by 2x or more.

 

Si72xx sensors can be configured, measured and controlled over an I 2C interface, providing greater flexibility during design and in the end product. Using an I 2C interface reduces current for position-sensing applications by enabling the sensor to be queried as needed instead of continuously.

 

The sensors include capabilities such as a tamper threshold feature that enables systems to detect attempts to bypass security. Most reed switch and Hall-effect sensor-based security systems can be defeated by a strong external magnetic field. The Si72xx sensors’ tamper detection technology detects anomalous magnetic fields, and a built-in self-test mode can be used to verify the sensor’s continued accurate operation in