Integrated, nanopower magnetoresistive sensors cut costs, offer new detection options

May 20, 2014 // By Graham Prophet
Honeywell has introduced a nanopower anisotropic magnetoresistive sensor IC; the technology provides position detection based on magnetic field sensing, using a very small and low-cost package, with on-chip integration of level detection and switching to give a simple on/off output and to replace reed switches where they are still the only option.

The device's high sensitivity, Honeywell says, allows you to cut costs, and to use the sensors in battery operated equipment with extremely low power requirements, where the solid state, non-contact design provides a reliable, durable alternative to reed switches.

The Nanopower Anisotropic Magnetoresistive Sensor ICs provide the highest level of magnetic sensitivity (as low as 7 Gauss typical) while requiring nanopower (360 nA average, in a typical reed-switch-replacement application). Smaller and more durable and reliable than reed switches, at the same sensitivity and essentially the same cost, the new sensor ICs can be deployed where previously only reed switches could be used for reasons of low power requirements and large air gap needs. The 360 nA figure is based on a 0.015% duty cycle of typically 15 µsec wake/100 msec sleep cycle.

Response time is not specified in the initial data sheet; the 100 msec cycle appears chosen to match the requirements of a typical reed-switch application, detecting whether or not (say) a door is open or closed, within 1/10th of a second. The 15 µsec on-time implies an actual detection in single-figures-µsecs, which could support detection of events at up to (perhaps) around 100 kHz – at the cost of running the device at its on-state current, which is 1 mA typical – sleep current is 160 to 260 nA over the supply voltage range.

These ICs’ higher sensitivity can function over air gaps twice the distance that Hall-effect sensors can accomodate. The higher sensitivity improves design flexibility and can offer significant application cost savings by utilising smaller or lower strength magnets.

 

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