Magnetic sensors get smarter for IoT-connected systems
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 I2C interface, providing greater flexibility during design and in the end product. Using an I2C 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 the field. Si72xx sensors also include a ±1 °C accurate temperature sensor, eliminating the need for discrete temperature sensing, reducing system size and cost, and enhancing functionality.
The Si72xx sensor portfolio includes three families:
– The Si720x family supports digital output switch and latch capabilities in a variety of sampling rates and sensitivities. These sensors are intended for applications requiring a periodic on-off signal with the change of a magnetic field.
– The Si721x family includes linear output devices for position-sensing applications that produce signals directly proportional to the strength of the magnetic field. These sensors support different gains and output types including analogue, pulse-width modulation (PWM) and the SENT protocol for automotive communications.
– The Si7210 family of I2C-configurable sensors supports all of the features and capabilities of the other two families with flexibility and programmability.
In industry-standard 3- and 5-pin SOT-23 packages, Si72xx sensor pricing begins at $0.45 (10,000). The Si72xx-WD-KIT wheel demo kit is priced at $149; it includes a pre-programmed EFM32 Happy Gecko STK, a wheel demo expansion board and six postage stamp-sized boards to evaluate the various Si72xx sensor types.
Silicon Labs; www.silabs.com/magnetic-sensors
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