iC-MH8
12 BIT ANGULAR HALL ENCODER
Rev A0.9, Page 11/25
Sensor principle
In conjunction with a rotating permanent magnet, the
iC-MH8 module can be used to create a complete en-
coder system. A diametrically magnetized, cylindri-
cal permanent magnet made of neodymium iron boron
(NdFeB) or samarium cobalt (SmCo) generates op-
timum sensor signals. The diameter of the magnet
should be in the range of 3 to 6 mm.
The iC-MH8 has four Hall sensors adapted for angle
determination and to convert the magnetic field into
a measurable Hall voltage. Only the z-component of
the magnetic field is evaluated, whereby the field lines
pass through two opposing Hall sensors in the oppo-
site direction. Figure 2 shows an example of field vec-
tors. The arrangement of the Hall sensors is selected
so that the mounting of the magnets relative to iC-MH8
is extremely tolerant. Two Hall sensors combined pro-
vide a differential Hall signal. When the magnet is ro-
tated around the longitudinal axis, sine and cosine out-
put voltages are produced which can be used to deter-
mine angles.
z
y
+Bz
B
x
-Bz
C151107-1
Figure 2: Sensor principle
Position of the Hall sensors and the analog sensor signal
The Hall sensors are placed in the center of the QFN28 In order to calculate the angle position of a diametri-
package at 90° to one another and arranged in a circle cally polarized magnet placed above the device a dif-
with a diameter of 2 mm as shown in Figure 3.
ference in signal is formed between opposite pairs of
Hall sensors, resulting in the sine being VSIN = VPSIN
-
VNSIN and the cosine VCOS = VPCOS - VNCOS. The zero
angle position of the magnet is marked by the resulting
cosine voltage value being at a maximum and the sine
voltage value at zero.
Pin 1 Mark
28 27 26 25 24 23 22
21
20
19
18
17
16
15
1
2
PSIN
PCOS
3
4
5
6
7
This is the case when the south pole of the magnet is
exactly above the PCOS sensor and the north pole is
above sensor NCOS, as shown in Figure 4. Sensors
PSIN and NSIN are placed along the pole boundary so
that neither generate a Hall signal.
NCOS
NSIN
(top view)
8
9
10 11 12 13 14
C040907-2
Figure 3: Position of the Hall sensors
When a magnetic south pole comes close to the sur-
face of the package the resulting magnetic field has a When the magnet is rotated counterclockwise the
positive component in the +z direction (i.e. from the top poles then also cover the PSIN and NSIN sensors, re-
of the package) and the individual Hall sensors each sulting in the sine and cosine signals shown in Figure
generate their own positive signal voltage.
5 being produced.
ICHAUS [ IC-HAUS GMBH ]
