iC-MZ
DIFFERENTIAL HALL SWITCH
Rev A2, 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 = µ
0
·
H at the two Hall sensors, dependent
on angle of rotation
φ
of the gear wheel. In an ensuing
amplification process analog signals V
A
and V
NA
are
formed from the differential signal; digital signals V
D
and V
ND
are generated by the back-end comparator
with hysteresis.
B
1
S1
gear wheel
P
B
2
S2
iC-MZ
bias magnet
N
S
B
B
2
B
1
bias
field
B
1
-B
2
B
T,hi
B
T,l o
0
P/2
P
3P/2
V
V
NA
V
A
V
dc
0
P/2
P
3P/2
V
B
V
D
P/2
P
V
B
3P/2
V
ND
P/2
P
3P/2
Figure 9: Gear wheel scanning
ICHAUS [ IC-HAUS GMBH ]
