ams AG AS5045 Operation Manual - Page 4

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AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Adapter PCB Operation Manual

5 Principle of Operation

3.9 mm

Circle of Hall elements

on chip: 2.2mm diameter

2.433 mm

Area of allowed magnet

misalignment: 0.5mm diameter

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).

Revision A.02, 14-Mar-07

The AS5045 chip consists of a ring of hall

3.9 mm

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

Defined

signal processor (DSP), which calculates the

center

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

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