as5045 austriamicrosystems, as5045 Datasheet - Page 15

• Manufacturer Part Number: as5045
• Description: 12-bit Programmable Magnetic Rotary Encoder
• Manufacturer: austriamicrosystems

AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
13.2
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)
and
MODE = 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:
*1
3 sigma represents 99.73% of readings.
13.3
13.3.1
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
Revision 1.2, 03-Oct-06
: statistically, 1 sigma represents 68.27% of readings,
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.
0.03 degrees rms (1 sigma)
Transition Noise
High Speed Operation
Sampling Rate
*1
in fast mode (pin MODE = high)
*1
in slow mode (pin
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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.
13.4
The propagation delay is the delay between the time that
the sample is taken until it is converted and available as
angular data. This delay is 96µs in fast mode and 384µs
in slow mode.
Using the SSI interface for absolute data transmission,
an additional delay must be considered, caused by the
asynchronous sampling (0 … 1/f
takes the external control unit to read and process the
angular data from the chip (maximum clock rate = 1MHz,
number of bits per reading = 18).
13.4.1
A rotating magnet will cause an angular error caused by
the output propagation delay.
This error increases linearly with speed:
where
e
rpm = rotating speed [rpm]
prop.delay = propagation delay [seconds]
Note: since the propagation delay is known, it can be
automatically compensated by the control unit processing
the data from the AS5045.
e
n
n
sampling
sampling
slow
fast
mod
mod
,
e
e
=
= angular error [°]
=
=
Propagation Delays
Angular Error Caused by Propagation Delay
rpm
rpm
rpm
∗
6
60
⋅
⋅
60
*
96
384
prop
μ
μ
s
.
s
delay
sample
) and the time it
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