as5040 austriamicrosystems, as5040 Datasheet - Page 20

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

AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
13.1 Physical Placement of the Magnet
The best linearity can be achieved by placing the center
of the magnet exactly over the defined center of the IC
package as shown in Figure 21:
Magnet Placement:
The magnet’s center axis should be aligned within a
displacement radius R
center of the IC with reference to the edge of pin #1 (see
Figure 21). This radius includes the placement tolerance
of the chip within the SSOP-16 package (+/- 0.235mm).
The displacement radius R
the center of the chip (see section 11: Alignment Mode)
The vertical distance should be chosen such that the
magnetic field on the die surface is within the specified
limits (see Figure 20). The typical distance “z” between
the magnet and the package surface is 0.5mm to 1.8mm
with the recommended magnet (6mm x 2.5mm). Larger
gaps are possible, as long as the required magnetic field
strength stays within the defined limits.
A magnetic field outside the specified range may still
produce usable results, but the out-of-range condition
will be indicated by MagINCn (pin 1) and MagDECn (pin
2), see Table 3.
Revision 1.8
Die surface
2.433 mm
2.433 mm
Figure 21: Defined IC center and magnet displacement radius
N
Figure 22: Vertical placement of the magnet
Package surface
1
S
Area of recommended maximum
magnet misalignment
3.9 mm
d
of 0.25mm from the defined
d
is 0.485mm with reference to
z
1.282mm ± 0.15mm
0.576mm ± 0.1mm
R
d
Defined
center
3.9 mm
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14 Simulation Modelling
With reference to Figure 23, a diametrically magnetized
permanent magnet is placed above or below the surface
of the AS5040. 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 AS5040. 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 23).
In order to neglect the influence of external disturbing
magnetic fields, a robust differential sampling and
Θ
The differential signal Y1-Y2 will give a sine vector of
Figure 23: Arrangement of Hall sensor array on chip (principle)
±0.235mm
=
2.433 mm
arctan
AS5040 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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