AS5045

Data Sheet

www.austriamicrosystems.com

Revision 1.7

28 – 33

17.2 Transition Noise

Transition noise is defined as the jitter in the transition between two steps.

Due to the nature of the measurement principle (Hall sensors + Preamplifier + ADC), there is always a certain degree

of noise involved.

This transition noise voltage results in an angular transition noise at the outputs. It is specified as 0.06 degrees rms

(1 sigma)

open).

This is the repeatability of an indicated angle at a given mechanical position.

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 implementing averaging of

readings. An averaging of 4 readings will reduce the transition noise by 6dB or 50%, e.g. from 0.03°rms to

0.015°rms (1 sigma) in slow mode.

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.

17.3 High Speed Operation

17.3.1 Sampling Rate

The AS5045 samples the angular value at a rate of 2.61k (slow mode) or 10.42k (fast mode, selectable by pin

MODE) samples per second. Consequently, the absolute outputs are updated each 384µs (96µs in fast mode).

At a stationary position of the magnet, the sampling rate creates no additional error.

Absolute Mode

At a sampling rate of 2.6kHz/10.4kHz, the number of samples (n) per turn for a magnet rotating at high speed can be

calculated by

s

rpm

n

e

slow

μ

384

60

mod

⋅

=

s

rpm

n

e

fast

μ

96

60

mod

⋅

=

The upper speed limit in slow mode is ~6.000rpm and ~30.000rpm in fast mode. The only restriction at high speed is

that there will be fewer samples per revolution as the speed increases (see Table 2).

Regardless of the rotational speed, the absolute angular value is always sampled at the highest resolution of 12 bit.