iC-MH8
12 BIT ANGULAR HALL ENCODER
Rev A0.9, Page 15/25
Test Mode: Analog REF
the Hall sensor signals. VBG is the internal bandgap
reference (1.24 V), with VOSR (0.5 V) used to gener-
ate the range of the offset settings. Bias current IBM
determines the internal current setting of the analog
circuitry. In order to compensate for variations in this
current and thus discrepancies in the characteristics
of the individual iC-MH8 devices (due to fluctuations in
production, for example), this can be set within a range
of -40% to +35% using register parameter CIBM. The
nominal value of 200 µA is measured as a short-circuit
current at pin B to ground.
iC-MH8
A
B
Z
VREF
~ 2.5 V
IBM
VBG
VOSR
~ 1.24 V
~ 0.5 V
U
~ 200 µA
VNA
C021107-4acr
Test mode Digital CLK
If, due to external circuitry, it is not possible to mea-
sure IBM directly, by way of an alternative clock signal
CLKD at pin A can be calibrated to a nominal 1 MHz
in this test mode via register value CIBM.
Figure 10: Setting bias current IBM in test mode
Analog REF
Calibration procedure
The calibration procedure described in the following
applies to the optional setting of the internal analog
sine and cosine signals and the mechanical adjust-
ment of the magnet and iC-MH8 in relation to one an-
other.
Vsin
+2 V
BIAS SETTING
a
The BIAS setting compensates for possible manufac-
turing tolerances in the iC-MH8 devices. A magnetic
field does not need to be present for this setting which
can thus be made either prior to or during the assem-
bly of magnet and iC-MH8.
-2 V
+2 V
Vcos
If the optional setup process is not used, register CIBM
should be set to an average value of 0x8 (which is
equivalent to a change of 0%). As described in the
previous section, by altering the value in register CIBM
in test mode Analog REF current IBM is set to 200 µA
or, alternatively, in test mode Digital CLK signal CLKD
is set to 1 MHz.
-2 V
C141107-1
Figure 11: Ideal Lissajous curve
CALIBRATION USING ANALOG SIGNALS
In test mode Analog OUT as shown in Figure 5 the in-
ternal signals which are transmitted to the sine/digital
converter can be tapped with high impedance. With
a rotating magnet it is then possible to portray the dif-
ferential signals VSIN and VCOS as an x-y graph (Lis-
sajous curve) with the help of an oscilloscope. In an
ideal setup the sine and cosine analog values describe
a perfect circle as a Lissajous curve, as illustrated by
Figure 11.
MECHANICAL ADJUSTMENT
iC-MH8 can be adjusted in relation to the magnet in
test modes Analog SIN and Analog COS, in which the
Hall signals of the individual Hall sensors can be ob-
served while the magnet rotates.
In test mode Analog SIN the output signals of the sine
Hall sensors which are diagonally opposite one an-
other are visible at pins A, B, Z and U. iC-MH8 and
the magnet are then adjusted in such a way that dif- At room temperature and with the amplitude control
ferential signals VPSIN and VNSIN have the same am- switched off (ENAC = 0) a rough GAING setting is se-
plitude and a phase shift of 180°. The same applies lected so that at an average fine gain of GAINF = 0x20
to test mode Analog COS, where differential signals (a gain factor of ca. 4.5) the Hall signal amplitudes are
VPCOS and VNCOS are calibrated in the same manner.
as close to 1 V as possible. The amplitude can then
ICHAUS [ IC-HAUS GMBH ]
