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MagAlpha SENSORS OVERVIEW
MagAlpha angle sensors offer the following advantages:
• Instantaneous angle sensing: up to 1μs sample rate, only 10μs latency at 100kRPM
• High resolution up to 14 bits
• Support for shaft rotation speeds from zero to over 100kRPM
• Wide magnetic field range support from 15mT to 150mT working range
• End- and side-shaft sensor topologies
• Low power consumption: 3.3V, 12mA
• Small form factor: 3x3mm QFN-16 package
Traditional magnetic angle sensors use a set of Hall plates orientated in the x- and y-axes that convert
the amplitude of the rotating magnetic field into a sine and a cosine waveform. The two waveforms are
then digitized with analog-to-digital converters (A-to-D), and the angle is computed using an arc tangent
calculation. This approach has some disadvantages. Firstly, the amplitude of the magnetic field being
measured musy be matched to the A-to-D converter’s input range for best results. This limits the min-
imum and maximum range of the magnetic field that can be accommodated and the magnet’s distance
from the sensor. The second major disadvantage is that the A-to-D conversion and arc tangent calcula-
tion take some time, which translates to angle error or position lag at the sensor output. Typical latency
can be hundreds of microseconds for this older technique.
MagAlpha sensors in contrast utilize an array of Hall plates that are sampled successively at very high
speeds in such a way that the signal phase represents the angle to be measured. The “phase-to-digital”
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technique captures the angle instantaneously every 1μs without the need for A-to-D conver-
sion or arc tangent calculation. This means the sensor is able to work over a wider magnetic field range
(typically 30-150mT), giving greater flexibility and tolerance for magnet positioning.
The fast Hall sampling and subsequent digital conditioning result in very low latency from Hall array
sampling to the data availability at the sensor output. Typical latency is only 10μs at a constant rotation
speed, allowing MagAlpha sensors to operate in systems with high rotation speed or that require fast
position control loops. Rotation speeds from zero to more than 100kRPM are possible.
Side-Shaft Capability
MagAlpha sensors support both end-of-shaft and side-of-shaft topologies. In end-of-shaft the sensor
is placed directly below the magnet connected to the rotating shaft. This topology gives the best perfor-
mance but is not always mechanically convenient because the end of a rotating shaft may not be accessi-
ble. For example, in a motor, it may be hidden by the shaft bearing, or driving into a gear box.
Side-shaft topology allows the magnet to be placed to the side of a ring magnet mounted on the rotating
shaft. This is advantageous for many designs as the ring can be located anywhere on the shaft, which
allows the sensor to be embedded more easily within the motor or product casing. MagAlpha sensors
contain dedicated bias trimming register, which allow the extra magnetic fields seen in side-shaft mode
to be normalized in amplitude so that the sensor maintains a linear output response over the full angle
measurement range (see Figure 6, page 11).
Advantages of MagAlpha Sensors
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