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Speed sensor integrates tracking capacitor

Posted: 13 Jul 2004 ?? ?Print Version ?Bookmark and Share

Keywords:allegro Microsystems? analog speed sensor? a1425?

Targeting automotive and industrial applications, Allegro MicroSystems Inc. has announced the availability of its new high-accuracy analog speed sensor with integrated tracking capacitor and dual zero-crossing output signal. Applications include automotive crankshaft speed sensing using ring magnets.

This ac-coupled differential sensor with on-chip capacitor is a true zero-crossing detector; the output switches precisely when the difference in magnetic field strength between the two Hall elements is zero. A unique dual-comparator scheme provides for accurate switching at the zero crossing on both the positive and negative going regions of the differential signal, while utilizing hysteresis to prevent false switching. These accurate switch-points are maintained over the entire automotive temperature range by an on-chip temperature compensation circuit.

When coupled with a back-biasing magnet, the sensor can be configured to turn on or off with the leading or trailing edge of a gear-tooth or slot. Two integrated Hall transducers sense changes in fields on the magnet face caused by a moving ferrous mass and are differentially amplified by on-chip electronics.

This differential sensing design provides immunity to radial vibration within the device's operating air gap. Steady-state magnet and system offsets are eliminated using an on-chip differential bandpass filter, which also provides relative immunity to interference from electromagnetic sources. The company says the on-chip temperature compensation and Schmitt trigger guarantees optimal operation to low frequencies over a wide range of air gaps and temperatures.

The A1425 is priced at $1.21 in quantities of less than 100,000. Delivery is 22 weeks.

- Gina Roos


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