IC-MZ_11 datasheet(9/11 Pages) ICHAUS

9 / 11 page

iC-MZ

DIFFERENTIAL HALL SWITCH

Rev A3, Page 9/11

APPLICATION EXAMPLES

Gear wheel scanning

Logging the position and rotation of a gear wheel with

iC-MZ requires that the gear wheel is made of a soft

magnetic basic material with which a magnetic ﬁeld

applied externally through the gear geometry can be

modulated. The strength of the modulation is greatest

at the gear rim, calling for iC-MZ to be placed at the

shortest possible operating distance to the gear wheel.

The necessary external bias ﬁeld is generated by a

back bias magnet placed behind iC-MZ. The magnet

should be positioned central to the package so that the

two Hall sensors are impinged by equal magnetic ﬁeld

strengths and a ﬁeld strength offset is avoided; the lat-

ter would make a greater difference in modulation ﬁeld

strength necessary for switching purposes. Field ho-

mogeneity can be improved by placing a pole piece

between the magnet and iC-MZ.

The strength of the magnetic ﬁeld modulation depends

not just on the operating distance and the intensity of

the bias ﬁeld but also on the module and addendum

of the gear wheel. The distance of the teeth along the

perimeter of the wheel stipulates the cycle with which

the magnetic ﬁeld strength is modulated. An optimum

modulation depth is achieved when the gear wheel ge-

ometry is selected so that the two Hall sensors on the

chip are opposite a tooth or a gap and the sensors pro-

vide signals in antiphase. With the given iC-MZ sensor

distance of 2 mm a tooth distance of about 4 mm is ad-

vantageous but not imperative. Even if the geometry of

the wheel is not adapted to suit the sensor, the signals

generated by the two Hall sensors share a ﬁxed phase

relation.

Figure 9 illustrates the typical course of magnetic in-

duction B = µ0 · H at the two Hall sensors, dependent

on angle of rotation φ of the gear wheel. In an ensuing

ampliﬁcation process analog signals VA and VNA are

formed from the differential signal; digital signals VD

and VND are generated by the back-end comparator

with hysteresis.

BT,hi

B-B

iC-MZ

bias magnet

bias

field

gear wheel

P/2

3P/2

P/2

3P/2

BT,lo

P/2

3P/2

P/2

3P/2

Figure 9: Gear wheel scanning

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