AS5035 – 64 PPR INCREMENTAL MAGNETIC ROTARY ENCODER

Revision 1.5

www.austriamicrosystems.com

Page 7 of 17

8

Simulation Modelling

Figure 9: Arrangement of Hall sensor array on chip (principle)

With reference to Figure 9, a diametrically magnetized

permanent magnet is placed above or below the surface

of the AS5035. 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

5

.

0

2

1

2

1

arctan

X

X

Y

Y

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 AS5035. 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 11)

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

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

±75mT at the

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.

9

Choosing the Proper Magnet

Typically the magnet should be 6mm in diameter and

≥2.5mm in height. Magnetic materials such as rare earth

AlNiCo, SmCo5 or NdFeB are recommended.

Magnet axis

Vertical field

component

(45…75mT)

0

360

360

Bv

Vertical field

component

R1 concentric circle;

radius 1.1mm

R1

Magnet axis

typ. 6mm diameter

S

N

Figure 10: Typical magnet and magnetic field distribution

AS5040 die

1

Radius of circular Hall sensor

array: 1.1mm radius

Center of die

2.433 mm

±0.235mm

3.9 mm

±0.235mm

X1

Y1

X2

Y2