www.ams.com/AS5311

Revision 1.12

19 - 29

AS5311

Datasheet - A pp l ic a t io n I n f or m a t i on

8.1 Magnetization

The AS5311 accepts magnetic multi-pole strip or ring magnets with a pole length of 1.0mm. Recommended magnet materials include plastic or

rubber bonded ferrite or Neodymium magnets.

It is not recommended to use the AS5311 with other pole lengths as this will create additional non-linearities.

Figure 12. Additional Error from Pole Length Mismatch

Figure 12 shows the error caused by a mismatch of pole length. Note that this error is an additional error on top of the chip-internal INL and DNL

errors (see Electrical System Specifications on page 8). For example, when using a multi-pole magnet with 1.2mm pole length instead of 1.0mm,

the AS5311 will provide 1024 incremental steps or 4096 absolute positions over 2.4mm, but with an additional linearity error of up to 50µm.

The curvature of ring magnets may cause linearity errors as well due to the fact that the Hall array on the chip is a straight line while the poles on

the multi-pole ring are curved. These errors decrease with increasing ring diameter. It is therefore recommended to keep the ring diameter

measured at the location of the Hall array at 20mm or higher.

8.2 Position of the Index Pulse

An index pulse is generated when the North and South poles are placed over the Hall array as shown in Figure 14.

The incremental output count increases when the magnet is moving to the left, facing the chip with pin#1 at the lower left corner (see Figure 14 -

top drawing). At the same time, the absolute position value increases. Likewise, the position value decreases when the magnet is moved in the

opposite direction.

AS5311 Systematic Linearity Error Caused by Pole

Length Deviation

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

750

800

850

900

950

1000 1050 1100 1150 1200 1250

Pole Length [µm]

Error [µm]

Error [µm]