as5040 austriamicrosystems, as5040 Datasheet - Page 21

• Manufacturer Part Number: as5040
• Description: 10-bit Programmable Magnetic Rotary Encoder
• Manufacturer: austriamicrosystems

AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
ratiometric calculation algorithm has been implemented.
The differential sampling of the sine and cosine vectors
removes any common mode error due to DC components
introduced by the magnetic source itself or external
disturbing magnetic fields. A ratiometric division of the
sine and cosine vectors removes the need for an
accurate absolute magnitude of the magnetic field and
thus accurate Z-axis alignment of the magnetic source.
The recommended differential input range of the
magnetic field strength (B
surface of the die. In addition to this range, an additional
offset of ±5mT, caused by unwanted external stray fields
is allowed.
The chip will continue to operate, but with degraded
output linearity, if the signal field strength is outside the
recommended range. Too strong magnetic fields will
introduce errors due to saturation effects in the internal
preamplifiers. Too weak magnetic fields will introduce
errors due to noise becoming more dominant.
15 Failure Diagnostics
The AS5040 also offers several diagnostic and failure
detection features:
15.1 Magnetic Field Strength Diagnosis
By software: the MagINCn and MagDECn status bits will
both be high when the magnetic field is out of range.
By hardware: Pins #1 (MagINCn) and #2 (MagDECn) are
open-drain outputs and will both be turned on (= low with
external pull-up resistor) when the magnetic field is out
of range. If only one of the outputs is low, the magnet is
either moving towards the chip (MagINCn) or away from
the chip (MagDECn).
15.2 Power Supply Failure Detection
By software: If the power supply to the AS5040 is
interrupted, the digital data read by the SSI will be all
“0”s. Data is only valid, when bit OCF is high, hence a
data stream with all “0”s is invalid. To ensure adequate
low levels in the failure case, a pull-down resistor
(~10kΩ) should be added between pin DO and VSS at
the receiving side.
By hardware: The MagINCn and MagDECn pins are
open drain outputs and require external pull-up resistors.
In normal operation, these pins are high ohmic and the
outputs are high (see Table 3). In a failure case, either
when the magnetic field is out of range or the power
supply is missing, these outputs will become low. To
Revision 1.8
(X1-X2)
,B
(Y1-Y2)
) is ±75mT at the
www.austriamicrosystems.com
ensure adequate low levels in case of a broken power
supply to the AS5040, the pull-up resistors (>10kΩ) from
each pin must be connected to the positive supply at pin
16 (VDD5V).
By hardware: PWM output: The PWM output is a
constant stream of pulses with 1kHz repetition frequency.
In case of power loss, these pulses are missing.
By hardware: Incremental outputs: In normal operation,
pins A(#3), B(#4) and Index (#6) will never be high at the
same time, as Index is only high when A=B=low.
However, after a power-on-reset, if VDD is powered up or
restarts after a power supply interruption, all three
outputs will remain in high state until pin CSn is pulled
low. If CSn is already tied to VSS during power-up, the
incremental outputs will all be high until the internal
offset compensation is finished (within t
16 Angular Output Tolerances
16.1 Accuracy
Accuracy is defined as the error between measured
angle and actual angle. It is influenced by several
factors:
As a sum of all these errors, the accuracy with centered
magnet = (Err
±0.5 degrees @ 25°C (see Figure 25).
Misalignment
accuracy. Figure 24 shows an example of a 3D-graph
displaying non-linearity over XY-misalignment. The
center of the square XY-area corresponds to a centered
magnet (see dot in the center of the graph). The X- and
Y- axis extends to a misalignment of ±1mm in both
directions. The total misalignment area of the graph
covers a square of 2x2 mm (79x79mil) with a step size of
100µm.
For each misalignment step, the measurement as shown
in Figure 25 is repeated and the accuracy
(Err
the Z-axis in the 3D-graph.
max
the non-linearity of the analog-digital converters,
internal gain and mismatch errors,
non-linearity due to misalignment of the magnet
– Err
min
max
)/2 (e.g. 0.25° in Figure 25) is entered as
of
– Err
the
min
)/2 is specified as better than
magnet
further reduces
PwrUp
).
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