AS5245 AMSCO [austriamicrosystems AG], AS5245 Datasheet - Page 27

• Manufacturer Part Number: AS5245
• Manufacturer: AMSCO [austriamicrosystems AG]

AS5245
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 18.
9.6.2 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)
= low or 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:
9.6.3 High Speed Operation
Sampling Rate.
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.
calculated by,
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
at the highest resolution of 12 bit.
www.austriamicrosystems.com/AS5245
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 0.03º rms to 0.015º 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 lower-
ing 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).
1. Statistically, 1 sigma represents 68.27% of readings; 3 sigma represents 99.73% of readings.
Example of Linearity Error Over 360º
-0.1
-0.2
-0.3
-0.4
-0.5
0.5
0.4
0.3
0.2
0.1
0
The AS5245 samples the angular value at a rate of 2.61k (slow mode) or 10.42k (fast mode, selectable by pin 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
1
55
109
163
217
(see Table
271
n
n
fastmode
slowomode
1
325
in fast mode (pin MODE = high) and 0.03 degrees rms (1 sigma) in slow mode (pin MODE
Err
7). Regardless of the rotational speed, the absolute angular value is always sampled
=
max
379
=
---------------------------------- -
rpm
433
-------------------------- -
rmp 96μs
Revision 1.3
⋅
487
60
⋅
60
(
384
541
)μs
Err
595
min
649
703
757
transition noise
811
865
919
973
(EQ 3)
(EQ 4)
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