as5046 austriamicrosystems, as5046 Datasheet - Page 31

• Manufacturer Part Number: as5046
• Description: Programmable 12-bit 360? Magnetic Angle Encoder With Absolute 2-wire Serial And Analog Interfaces
• Manufacturer: austriamicrosystems

AS5046 Programmable 360° Magnetic Angle Encoder – Preliminary Data Sheet
In practice, there is no upper speed limit. The only restriction is
that there will be fewer samples per revolution as the speed
increases.
Regardless of the rotational speed, the absolute angular value is
always sampled at the highest resolution.
18.5 Output Delays
The propagation delay is the delay between the time that
the sample is taken until it is available as angular data.
This delay is 96µs in fast mode (pin Mode = high) and
384µs in slow mode (pin Mode = low or open)
The analog output produces no further delay, the output
voltage will be updated as soon as it is available. Using
the serial interface for data transmission, an additional
delay must be considered, caused by the asynchronous
sampling (0….1/f
control unit to read and process the angular data from
the AS5046.
18.5.1
A rotating magnet will cause an angular error caused by
the propagation delay.
This error increases linearly with speed:
where
Note: since the propagation delay is known, it can be
automatically compensated by the control unit processing
the data from the AS5046.
Revision 1.0
e
Fast Mode
(pin Mode = 1)
610rpm = 1024 samples / turn
1220rpm = 512 samples / turn
2441rpm = 256 samples / turn
etc…
sampling
(deg)
e
rpm = rotating speed [rpm]
prop.delay = propagation delay [seconds]
Angular Error Caused by Propagation
Delay
sampling
=
Table 10: Speed performance
sample
= angular error [°]
6
∗
rpm
) and the time it takes the external
∗
pr
Slow Mode
(pin Mode = 0 or open)
610rpm = 256 samples / turn
1220rpm = 128 samples / turn
2441rpm = 64 samples / turn
etc…
.
delay
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18.6 Internal Timing Tolerance
The AS5046 does not require an external ceramic
resonator or quartz. All internal clock timings for the
AS5046 are generated by an on-chip RC oscillator. This
oscillator is factory trimmed to ±5% accuracy at room
temperature (±10% over full temperature range). This
tolerance influences the ADC sampling rate:
18.6.1
A new angular value is updated every
96µs +/- 5% (Mode = 1) or
384µs +/- 5% (Mode = 0 or open)
18.7 Temperature
18.7.1
One of the major benefits of the AS5046 compared to
linear Hall sensors is that it is much less sensitive to
temperature. While linear Hall sensors require a
compensation of the magnet’s temperature coefficients,
the AS5046 automatically compensates for the varying
magnetic field strength over temperature. The magnet’s
temperature drift does not need to be considered, as the
AS5046 operates with magnetic field strengths from
±45…±75mT.
Example:
A NdFeB magnet has a field strength of 75mT @ –40°C and a
temperature coefficient of -0.12% per Kelvin. The temperature
change is from –40° to +125° = 165K.
The magnetic field change is: 165 x -0.12% = -19.8%, which
corresponds to 75mT at –40°C and 60mT at 125°C .
The AS5046 can compensate for this temperature related
field strength change automatically, no user adjustment
is required.
18.7.2
The influence of temperature in the absolute accuracy is
very low. While the accuracy is ≤ ±0.5° at room
temperature, it may increase to ≤±0.9° due to increasing
noise at high temperatures.
18.7.3
The internal RC oscillator is factory trimmed to ±5%.
Over temperature, this tolerance may increase to ±10%.
Generally, the timing tolerance has no influence in the
accuracy or resolution of the system, as it is used mainly
for internal clock generation.
Absolute Output; Serial Interface
Magnetic Temperature Coefficient
Accuracy over Temperature
Timing Tolerance over Temperature
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