Magnetoresistive sensors require nanoamps to replace reed switches

May 20, 2014 // By Peter Clarke
Honeywell Sensors and Control, a division of Honeywell International Inc. (Morristown, New Jersey), has introduced a family of ICs comprising what it claims is the lowest power and highest sensitivity anisotropic magnetoresistive sensors.

The sensors provide a binary output - engaged or not engaged - and can replace reed switches in numerous applications and with current draw in the range 300- to 400-nanoamps the sensors are suitable for battery-operated equipment, the company claimed.

The Nanopower family includes two components both housed in a SOT-23 package.

The SM351LT has a sensitivity of 7 gauss and 11 gauss maximum with a typical current draw of 360nA. The SM353LT is sensitive to 14 gauss and has a maximum operational tolerance of 20 gauss with a lower typical current draw of 310nA.

Potential applications are vast include counting, metering and flow sensing, anti-tamper switches, door and window closed sensors and position sensing in industrial equipment.

Omnipolarity allows the sensor to be activated by either a north or south pole while the push-pull CMOS output does not require external resistors The sensitivity of the sensors means that they can be sited further away from a magnet than would be the case with a Hall Effect sensor and can be used with ferrite magnets, not requiring stronger rare-earth enriched magnetics, said James McKenna, product director for sensors in Europe.

The devices work from a voltage supply of 1.65V to 5.5V and across a temperature range of -40 degrees C to 85 degrees C.

Murata and Anasem provide competing magnetoresistive products while Allegro Microsystems, Infineon, Diodes Inc. and Melexis provide Hall Effect sensors of similar functionality. Honeywell has also introduced a Hall Effect sensor the SL353LT. However, compared with magnetoresistive and Hall Effect competition that consumes 3-microamps, the Nanopower series consumer about one tenth the power at equal or better sensitivity, said Honeywell.

The devices are smaller and more durable and reliable than reed switches, at the same sensitivity and essentially the same cost, of the order of 10 to 20 cents in volume. Honeywell said.

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