AS5304/AS5306 Integrated Hall IC for linear and off-axis rotary motion detection

Revision 1.5

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AS5306 Systematic Linearity Error caused by Pole

Length Deviation

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Pole Length [μm]

Error [µm]

AS5304 Systematic Linearity Error caused by Pole

Length Deviation

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Pole Length [μm]

Error [µm]

3.

It is therefore recommended to continue to the next (second) index position from the end of the strip (Index = high,

A=B= high). This position can now be used as a defined home position.

7.2

Incremental Hysteresis

If the magnet is sitting right at the transition point between two steps, the

noise in the system may cause the incremental outputs to jitter back and

forth between these two steps, especially when the magnetic field is

weak.

To avoid this unwanted jitter, a hysteresis has been implemented. The

hysteresis lies between 1 and 2 LSB, depending on device scattering.

Figure 8 shows an example of 1LSB hysteresis: the horizontal axis is the

lateral position of the magnet as it scans across the IC, the vertical axis

is the change of the incremental outputs, as they step forward (blue line)

with movement in +X direction and backward (red line) in –X direction.

Note: 1LSB = 25µm for AS5304, 15µm for AS5306

Figure 8:

Hysteresis of the incremental output

7.3

Integral Non-Linearity (INL)

The INL (integral non-linearity) is the deviation between indicated position and actual position. It is better than 1LSB for both

AS5304 and AS5306, assuming an ideal magnet. Pole length variations and imperfections of the magnet material, which lead to

a non-sinusoidal magnetic field will attribute to additional linearity errors.

7.3.1

Error Caused by Pole Length Variations

Figure 9 and Figure 10 show the error caused by a non-ideal

pole length of the multi-pole strip or ring.

This is less of an issue with strip magnets, as they can be

manufactured exactly to specification using the proper

magnetization tooling.

Figure 9:

Additional error caused by pole length variation: AS5304

However, when using a ring magnet (see Figure 1) the pole

length differs depending on the measurement radius. For

optimum performance it is therefore essential to mount the

IC such that the Hall sensors are exactly underneath the

magnet at the radius where the pole length is 2.0mm

(AS5304) or 1.2mm (AS5306), see also 8.1.2.

Note that this is an additional error, which must be added to

the intrinsic errors INL (see 7.3) and DNL (see 7.4).

Figure 10:

Additional error caused by pole length variation: AS5306

M agnet position

Hys teres is:

1 LSB

X +2

Increm en tal

o utput

Mov ement d ir ection: +X

M ovem ent direc tion: -X

X +4

X

X

X +1

X +3

X+1

X+2

X+ 3

X+4