A1425

The A1425 ac-coupled Hall-effect sensor is a monolithic integrated circuit that  switches in response to changing differential magnetic fi  elds created by rotating  ring magnets or, when coupled with a magnet, by ferrous targets. The device is a  true zero-crossing detector: the output switches precisely when the difference in  magnetic fi  eld strength between the two Hall elements is zero.  A unique dual- comparator scheme provides for accurate switching during zero-crossing, both  when the sensed fi  eld is increasing in strength and when it is decreasing, while  utilizing hysteresis to prevent false switching. The zero-crossing nature of this  device provides excellent repeatability for crankshaft applications.

Changes in fi  eld strength at the device face caused by a moving target are sensed  by the two integrated Hall transducers, generating signals that are differen- tially amplifi  ed by on-chip electronics. This differential sensing design provides  immunity to radial vibration within the operating air gap range of the A1425, by  rejection of the common mode signal. Steady-state magnet and system offsets are
eliminated using an on-chip differential band-pass fi  lter. This fi  lter also provides  relative immunity to interference from electromagnetic sources.