AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
Adapter PCB Operation Manual
Revision A.02, 14-Mar-07 www.austriamicrosystems.com
Page 3 of 12
5
Principle of Operation
The AS5045 chip consists of a ring of hall
elements, placed at the center of the IC at a
circle diameter of 2.2mm (86.6mil).
The hall elements pick up the field of a magnet,
placed atop this hall array circle. This
information is digitized and fed into a digital
signal processor (DSP), which calculates the
angle of the magnet with a resolution of 0.0879
degrees or 4096 positions per revolution (12bit)
at a sampling rate of 96µs (10kHz; Default) or
384µs (2.6kHz).
The digital angle information is available in
several formats: as serial 12-bit data stream, as
pulse-width modulated (PWM) signal or as
quadrature incremental signal
Figure 4: Tolerances of magnet placement
5.1
Magnet considerations
A magnet, having one north / one south pole in the horizontal axis is placed right above the ring of hall elements
(see Figure 2). The magnet does not necessarily need to be circular, it can be rectangular as well, as long as the
north and south pole are arranged horizontally over the center of the hall array ring.
The magnetic field strength along this ring should be in the range of
±
45….75 milliTesla (mT).
5.1.1
Magnet size
The size of the magnet should be at least the size of the hall array ring (2.2mm). Smaller magnets are more critical
in terms of misalignment due to the non-linear magnetic field distribution along the circumference of the magnet.
The recommended magnet diameter is 4….6mm
5.1.2
Magnet distance and material
To achieve the required field strength at a reasonable distance (~0.5…5mm), it is recommended to use rare-earth
magnets, such as Samarium-Cobalt (SmCo) or Neodyne-Iron-Boron (NdFeB) magnets.
5.1.3
Magnet misalignment
In theory, the magnet misalignment is not critical for this type of angular measurement. In practice however,
magnets are not perfectly linear. The magnetic field strength does not increase linearly with the radius. As you get
towards the boundary of the magnet, the magnetic field comes to a maximum and then weakens as you move
further away from the center. Therefore, a magnet should be chosen, that is still in the linear range at a <3mm
diameter.
5.1.4
Non-linearity errors
A non-linear magnetic field results in a non-sinusoidal representation of the magnet, which in turn causes non-
linearities in the calculated angle (calculated angle differs from actual angle).
With a perfectly centered magnet, the maximum error is <
±
0,5 degrees. This error is caused by internal mismatch
and gain errors.
With the recommended 4mm magnet (Bomatec BMN-35H), the maximum error of <
±
1.4degrees (including
internal errors and temperature related errors) can be achieved while the magnet is off-center by a radius of
<0.25mm (see Figure 4).
1
Defined
center
2.433 mm
2.433 mm
3.9 mm
3.9 mm
Area of allowed magnet
misalignment: 0.5mm diameter
Circle of Hall elements
on chip: 2.2mm diameter
ams
AG
Technical
content
still
valid
