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AS5140H
Data Sheet - Detailed Description
In absolute mode (serial interface and PWM output), 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/+96祍. 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 192祍 as the DSP requires two sampling periods
(2x96祍) to synthesize and redistribute any missing pulses.
Incremental Mode. Incremental encoders are usually required to produce no missing pulses up to several thousand rpm. Therefore, the
AS5140H has a built-in interpolator, which ensures that there are no missing pulses at the incremental outputs for rotational speeds of up to
10.000 rpm, even at the highest resolution of 10 bits (512 pulses per revolution).
7.12.4 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 48祍
for the absolute interface and 192祍 for the incremental interface. Using the SSI interface for absolute data transmission, an additional delay
must be considered, caused by the asynchronous sampling (t=0&1/fs) and the time it takes the external control unit to read and process the
data.
Angular Error Caused by Propagation Delay. A rotating magnet will therefore cause an angular error caused by the output delay. This
error increases linearly with speed:
e
sampling
= rpm * 6 * prop.delay
(EQ 8)
Where:
e
sampling
= angular error [篯
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 that is processing the data from the
AS5140H, thus reducing the angular error caused by speed.
7.12.5 Internal Timing Tolerance
The AS5140H does not require an external ceramic resonator or quartz. All internal clock timings for the AS5140H are generated by an on-chip
RC oscillator. This oscillator is factory trimmed to ?% accuracy at room temperature (?0% over full temperature range). This tolerance
influences the ADC sampling rate and the pulse width of the PWM output:
Absolute output; SSI interface: A new angular value is updated every 100?/SPAN>s (typ.)
Incremental outputs: The incremental outputs are updated every 100?/SPAN>s (typ.)
PWM output: A new angular value is updated every 100?/SPAN>s (typ.). The PWM pulse timings T
on
and T
off
also have the same tolerance as the
internal oscillator. If only the PWM pulse width T
on
is used to measure the angle, the resulting value also has this timing tolerance. However,
this tolerance can be cancelled by measuring both T
on
and T
off
and calculating the angle from the duty cycle (see Pulse Width Modulation
(PWM) Output on page 16):
Position =
(EQ 9)
Table 21. Speed Performance
Absolute Output Mode
Incremental Output Mode
610rpm = 1024 samples / turn
No missing pulses
@ 10 bit resolution (512ppr):
max. speed = 10.000 rpm
122rpm = 512 samples / turn
2441rpm = 256 samples / turn
etc.
t
on
1025
?/DIV>
t
on
t
off
+
(
)
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