AS5045 datasheet(18/24 Pages) AMSCO

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AS5045 12-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.5

www.austriamicrosystems.com

Page 18 of 24

11 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.

The magnetic field strength perpendicular to the die

surface has to be in the range of ±45mT…±75mT (peak).

The magnet’s field strength should be verified using a

gauss-meter. The magnetic field Bv at a given distance,

along a concentric circle with a radius of 1.1mm (R1),

should be in the range of ±45mT…±75mT. (see Figure

17).

Magnet axis

Vertical field

component

(45…75mT)

360

Vertical field

component

R1 concentric circle;

radius 1.1mm

Magnet axis

typ. 6mm diameter

Figure 17: Typical magnet (6x3mm) and magnetic field distribution

11.1

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 chip

as shown in the drawing below:

Defined

center

2.433 mm

3.9 mm

Area of recommended maximum

magnet misalignment

Figure 18: Defined chip center and magnet displacement radius

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.

The magnet may be placed below or above the device.

The distance should be chosen such that the magnetic

field on the die surface is within the specified limits (see

Figure 17). The typical distance “z” between the magnet

and the package surface is 0.5mm to 1.5mm, provided

the use of the recommended magnet material and

dimensions (6mm x 3mm). Larger distances are possible,

as long as the required magnetic field strength stays

within the defined limits.

However, 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 1.

1.282mm ± 0.15mm

0.576mm ± 0.1mm

Package surface

Die surface

Figure 19: Vertical placement of the magnet

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