as5140 austriamicrosystems, as5140 Datasheet - Page 15

• Manufacturer Part Number: as5140
• Description: 10-bit 360? Programmable Magnetic Rotary Encoder For High Ambient Temperatures Up To 150?c
• Manufacturer: austriamicrosystems

AS5140H 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
13 Simulation Modelling
With reference to Figure 20, a diametrically magnetized
permanent magnet is placed above or below the surface
of the AS5140H. The chip uses an array of Hall sensors
to sample the vertical vector of a magnetic field
distributed across the device package surface. The area
of magnetic sensitivity is a circular locus of 1.1mm radius
with respect to the center of the die. The Hall sensors in
the area of magnetic sensitivity are grouped and
configured such that orthogonally related components of
the magnetic fields are sampled differentially.
the magnetic field. The differential signal X1-X2 will give
an orthogonally related cosine vector of the magnetic
field.
The angular displacement (Θ) of the magnetic source
with reference to the Hall sensor array may then be
modelled by:
The ±0.5° angular error assumes a magnet optimally
aligned over the center of the die and is a result of gain
mismatch errors of the AS5140H. Placement tolerances
of the die within the package are ±0.235mm in X and Y
direction, using a reference point of the edge of pin #1
(Figure 20).
In order to neglect the influence of external disturbing
magnetic fields, a robust differential sampling and
ratiometric calculation algorithm has been implemented.
The differential sampling of the sine and cosine vectors
Revision 1.1, 02-03-2007
Θ
The differential signal Y1-Y2 will give a sine vector of
Figure 20: Arrangement of Hall sensor array on chip (principle)
±0.235mm
=
2.433 mm
arctan
AS5140H die
(
(
X
Y
1
1
−
−
Radius of circular Hall sensor
array: 1.1mm radius
Y
1
X
3.9 mm ±0.235mm
2
2
)
)
±
0
5 .
X1
°
Y1
Y2
Center of die
X2
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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.
14 Failure Diagnostics
The AS5140H also offers several diagnostic and failure
detection features:
14.1 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).
14.2 Power Supply Failure Detection
By software: If the power supply to the AS5140H 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
ensure adequate low levels in case of a broken power
(X1-X2)
,B
(Y1-Y2)
) is ±75mT at the
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