as5045 austriamicrosystems, as5045 Datasheet - Page 16

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

AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
13.5
The AS5045 does not require an external ceramic
resonator or quartz. All internal clock timings for the
AS5045 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 and the
pulse width of the PWM output:
Revision 1.2, 03-Oct-06
Absolute output; SSI interface:
A new angular value is updated every 400µs (typ.)
PWM output:
A new angular value is updated every 400µs (typ.).
The PWM pulse timings T
same tolerance as the internal oscillator (see
above).
If only the PWM pulse width T
the angle, the resulting value also has this timing
tolerance.
However, this tolerance can be cancelled by
measuring both T
angle from the duty cycle (see section 5):
Position
Internal Timing Tolerance
=
t
(
t
on
on
⋅
+
on
4097
t
and T
off
)
−
off
on
1
and T
and calculating the
on
is used to measure
off
also have the
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13.6
13.6.1
One of the major benefits of the AS5045 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 AS5045 automatically compensates for the varying
magnetic field strength over temperature. The magnet’s
temperature drift does not need to be considered, as the
AS5045 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 AS5045 can compensate for this temperature related
field strength change automatically, no user adjustment
is required.
13.7
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.
13.7.1
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.
The only concern to the user is the width of the PWM
output pulse, which relates directly to the timing
tolerance of the internal oscillator. This influence
however can be cancelled by measuring the complete
PWM duty cycle instead of just the PWM pulse (see
13.5).
Temperature
Magnetic Temperature Coefficient
Accuracy over Temperature
Timing Tolerance over Temperature
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