AS5040 View Datasheet(PDF) - austriamicrosystems AG
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AS5040 Datasheet PDF : 33 Pages
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AS5040
Data Sheet
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:
n = 60
rpm ⋅ 96μs
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:
rpm
=
n
60
⋅ 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.
Absolute Mode with PWM:
The principle is the same as with the serial communication. The PWM output is refreshed with a rate of 1.025ms, the
number of samples (n) per turn for a magnet rotating at high speed can be calculated by:
n=
60
rpm ⋅1.025ms
In absolute mode with PWM output, 57 rpm is the maximum speed, where 1024 readings per revolution can be
obtained.
Incremental Mode:
Incremental encoders are usually required to produce no missing pulses up to several thousand rpm’s.
Therefore, the AS5040 has a built-in interpolator, which ensures that there are no missing pulses at the incremental
outputs for rotational speeds of up to 30,000 rpm, even at the highest resolution of 10 bits (512 pulses per revolution).
Table 7: Speed Performance
Absolute Output Mode
610rpm = 1024 samples / turn
1220rpm = 512 samples / turn
2441rpm = 256 samples / turn
etc…
Incremental Output Mode
no missing pulses
@ 10 bit resolution (512ppr):
max. speed = 30,000 rpm
Propagation Delays
The propagation delay is the delay between the time that a sample is taken until it is converted and available as
angular data. This delay is 48µs for the absolute interface and 192µs for the incremental interface.
Using the SSI interface for absolute data transmission, an additional delay must be considered, caused by the
asynchronous sampling (t= 0…1/fs) and the time it takes the external control unit to read and process the data.
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