AS5040 Datasheet, PDF (15/28 Pages) ams AG – 10 BIT 360° PROGRAMMABLE MAGNETIC ROTARY ENCODER

AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER
12.1 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 20:
3.9 mm
1
3.9 mm
2.433 mm
2.433 mm
Defined
center
R_d
Area of recommended maximum
magnet misalignment
Figure 20: Defined IC center and magnet displacement radius
13 Simulation Modelling
3.9 mm ±0.235mm
1
2.433 mm
±0.235mm
Y1
X1
X2
Y2
AS5040 die
Center of die
Radius of circular Hall sensor
array: 1.1mm radius
Figure 22: Arrangement of Hall sensor array on chip (principle)
Magnet Placement:
The magnet’s center axis should be aligned within a
displacement radius Rd of 0.25mm from the defined
center of the IC with reference to the edge of pin #1 (see
Figure 20). This radius includes the placement tolerance
of the chip within the SSOP-16 package (+/- 0.235mm).
The displacement radius Rd is 0.485mm with reference to
the center of the chip (see section 10: Alignment Mode)
The vertical distance should be chosen such that the
magnetic field on the die surface is within the specified
limits (see Figure 19). 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.
N
S
Die surface
Package surface
z
0.576mm ± 0.1mm
1.282mm ± 0.15mm
Figure 21: Vertical placement of the magnet
With reference to Figure 22, 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 differential signal Y1-Y2 will give a sine vector of
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:
Θ
=
arctan
(Y 1
(X1
−
−
Y 2)
X 2)
±
0.5°
Revision 1.6, 03-Oct-06
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