There are a few key considerations to note from the positions shown in Figure 2-2. The On-Axis case is the most ideal location for angle sensing using a single magnetic sensor. In this placement, the field is naturally parallel to the surface of the magnet and will reside entirely within the XY plane of the sensor. To achieve this placement, the diametric magnet is centered on the rotating shaft and the sensor is aligned exactly to the magnet's axis of rotation. This relationship will hold true in this position even when using a magnet with a non-circular profile.

Figure 2-2 Diametric Magnet Field Profiles

While the square faced magnet may be used in this location, it will otherwise not be recommended due to the non-sinusoidal nature of the input magnetic field. The square magnet is useful to help facilitate alignment during assembly of the end product. For any magnet profile, the primary benefit of on-axis alignment is that mechanical errors tend to have a lesser impact on the final angle measurement. This is demonstrated in Section 4.

Another option shown in Figure 2-1 is an In-Plane alignment. This is a very compact alignment option but produces inputs which are significantly mismatched. The resulting amplitude mismatch creates non-linearity of the angle calculation. TMAG5170 and TMAG5273 offer amplitude correction to minimize this effect. This alignment allows a dipole ring magnet to be installed anywhere along the rotating shaft, and this keeps the end of shaft free for use by the rest of the system. In-plane alignment enables angle measurement to be more easily integrated into a BLDC motor with minimal increase to the motor size.

The final placement option is shown as off-axis and represents any other location. Outside of the in-plane and off-axis alignments, there are any number of locations that will produce a measurable field with a component in all three Cartesian directions. The amplitude of each component will vary with location, but will remain sinusoidal and separated in phase from each other by 90 degree intervals. While there are positions which may be found that will produce equally balanced inputs, it should be expected that there will likewise be amplitude mismatch between the two axes used for angle calculation.