AS5040-ASST View Datasheet(PDF) - austriamicrosystems AG
Part Name
Description
MFG CO.
'AS5040-ASST' PDF : 61 Pages View PDF
AS5040 − Angular Output Tolerances
The transition noise has different implications on the type of
output that is used:
• Absolute Output; SSI Interface: The transition noise of the
absolute output can be reduced by the user by applying
an averaging of readings.
• PWM Interface: If the PWM interface is used as an analog
output by adding a low pass filter, the transition noise can
be reduced by lowering the cutoff frequency of the filter.
If the PWM interface is used as a digital interface with a
counter at the receiving side, the transition noise may
again be reduced by averaging of readings.
• Incremental Mode: In incremental mode, the transition
noise influences the period, width and phase shift of the
output signals A, B and Index. However, the algorithm
used to generate the incremental outputs guarantees no
missing or additional pulses even at high speeds (up to
30.000 rpm and higher).
ams Datasheet
[v2-12] 2017-Jun-20
High Speed Operation
Sampling Rate
The AS5040 samples the angular value at a rate of 10.42k
samples per second. Consequently, the incremental, as well as
the absolute outputs are updated each 96μs. At a stationary
position of the magnet, this sampling rate creates no additional
error.
Absolute Mode with Serial Communication
With the given sampling rate of 10.4 kHz, the number of samples
(n) per turn for a magnet rotating at high speed can be
calculated by:
(EQ5) n = -r--p---m-----6-⋅--0-9---6----μ----s
In practice, there is no upper speed limit. The only restriction is
that there will be fewer samples per revolution as the speed
increases.
Regardless of the rotational speed, the absolute angular value
is always sampled at the highest resolution of 10 bit.
Likewise, for a given number of samples per revolution (n), the
maximum speed can be calculated by:
(EQ6)
rpm
=
--------6---0--------
n ⋅ 96μs
In absolute mode with serial communication, 610 rpm is the
maximum speed, where 1024 readings per revolution can be
obtained.
In incremental mode, the maximum error caused by the
sampling rate of the ADCs is 0/+96μs. It has a peak of
1LSB = 0.35° at 610 rpm. At higher speeds this error is reduced
again due to interpolation and the output delay remains at
192μs as the DSP requires two sampling periods (2x96μs) to
synthesize and redistribute any missing pulses.
Page 47
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