Page 40 ams Datasheet
Document Feedback [v2-00] 2016-Feb-05
AS5145H/AS5145A/AS5145B − Application I nformation
• 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 can be
further 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
15,000 rpm and higher).
Note(s): Statistically, 1 sigma represents 68.27% of readings
and 3 sigma represents 99.73% of readings.
High Speed Operation
•Sampling Rate: The AS5145 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
nslowmode =
nfastmode =
The upper speed limit in slow mode is ~6,000 rpm and
~30,000 rpm in fast mode. The only restriction at high
speed is that there will be fewer samples per revolution
as the speed increases (see Figure 12). Regardless of the
rotational speed, the absolute angular value is always
sampled at the highest resolution of 12-bit.
• Incremental Mode: Incremental encoders are usually
required to produce no missing pulses up to several
thousand rpm. Therefore, the AS5145 has a built-in
interpolator, which ensures that there are no missing
pulses at the incremental outputs for rotational speeds of
up to 15,000 rpm, even at the highest resolution of 12 bits
(4096 pulses per revolution).