AS5040 datasheet(15/28 Pages) AMSCO

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AS5040 10-BIT PROGRAMMABLE MAGNETIC ROTARY ENCODER

Revision 1.6, 03-Oct-06

www.austriamicrosystems.com

Page 15 of 28

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:

Defined

center

2.433 mm

3.9 mm

Area of recommended maximum

magnet misalignment

Figure 20: Defined IC 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 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.

1.282mm ± 0.15mm

0.576mm ± 0.1mm

Package surface

Die surface

Figure 21: Vertical placement of the magnet

13 Simulation Modelling

Figure 22: Arrangement of Hall sensor array on chip (principle)

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:

(

)

()

−

arctan

AS5040 die

Radius of circular Hall sensor

array: 1.1mm radius

Center of die

2.433 mm

±0.235mm

3.9 mm

±0.235mm

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