AS5040

Data Sheet

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Revision 2.10

28 - 33

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:

s

rpm

n

μ

96

60

⋅

=

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:

s

n

rpm

μ

96

60

⋅

=

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:

ms

rpm

n

025

.

1

60

⋅

=

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

Incremental Output Mode

610rpm = 1024 samples / turn

1220rpm = 512 samples / turn

2441rpm = 256 samples / turn

etc…

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