MA700GQ-P Datasheet, PDF (7/15 Pages) MPS Industries, Inc. – Angular Sensor for Position Control with Side-Shaft Positioning Capability

MA700
Angular Sensor for Position Control with
Side-Shaft Positioning Capability
Table 2. In short, the front-end delivers in a
straightforward and open loop manner a digital number
proportional to the angle of the magnetic field at the
rate of 500 kHz.
Side-Shaft
The default current biasing of the Hall devices can be
adjusted by programming in order to accommodate low
field or compensate non-linearities inherent to side-
shaft configurations.
Figure 8: Hall Devices Biasing Diagram
In case the MA700 gets mounted in side-shaft con-
figuration, the relation between the field angle and the
mechanical angle is not directly linear anymore. This
effect is related to the fact that the tangential magnetic
field is usually smaller than the radial field. We define
the field ratio as:
,
where
, respectively , is the maximum radial,
respectively tangential, magnetic field (see Figure 9).
Figure 9: Side-Shaft Field
The ratio k depends on the magnet geometry and the
distance to the sensor.
The X-axis or the Y-axis bias current can be reduced in
order to recover an equal Hall signal for all angles and
therefore suppress the non-linearity. The current
reduction is set by the parameter Bias Current
Trimming BCT(7:0), which is an integer from 0 to 255.
For an optimum compensation the radial axis should be
reduced by the quantity:
TABLE 9 EXAMPLE OF OPTIMUM BCT SETTING
BCT(7:0)
0
1
…
128
…
255
Magnet ratio k
1
1.003
…
1.50
…
3.00
From the dot printed on the package it is possible to
know whether the radial field is detected by the sensor
X or Y component (see Figure 10).
Figure 10: Package Top View with X and Y Axes
First the user must determine which axis needs to be
reduced (see the qualitative field distribution around a
ring in Figure 9). For instance, with the arrangement
depicted in Figure 8, the X-axis should be reduced.
Then the parameter ETX or ETY can be set. Note that
if both ETX and ETY are set to 1 the current bias will
be reduced in both directions the same way, i.e.
without side-shaft correction.
TABLE 10 ETX AND ETY
ETX
Enable trimming the X axis
0
Disabled
1
Enabled
ETY
Enable trimming the Y axis
0
Disabled
1
Enabled
Monolithic Power Systems, Inc. | Gland, Switzerland | Tel: [phone] | [e-mail] | www.sensimatech.com
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Reserved. MA700 Rev 1.0 September 2014
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