AS5311

Data Sheet

www.austriamicrosystems.com

Revision 1.01

17 - 23

10.2 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.

10.3 Mounting the Magnet

10.3.1 Vertical Distance

As a rule of thumb, the gap between chip and magnet should be ½ of the pole length, that is Z=0.5mm for the

1.0mm pole length of the AS5311 magnets. However, the gap also depends on the strength of the magnet.

Typical gaps for AS5311 magnets range from 0.3 to 0.6mm (see 6.4).

The AS5311 automatically adjusts for fluctuating magnet strength by using an automatic gain control (AGC). The

vertical distance should be set such that the AS5311 is in the “green” range. See 7.5 for more details.

10.3.2 Alignment of Multi-pole Magnet and IC

When aligning the magnet strip or ring to the AS5311, the centerline of the magnet strip should be placed

exactly over the Hall array. A lateral displacement in Y-direction (across the width of the magnet) is acceptable

as long as it is within the active area of the magnet. See Figure 14 for the position of the Hall array relative to

Pin #1.

Note: the active area in width is the area in which the magnetic field strength across the width of the magnet is

constant with reference to the centerline of the magnet (see Figure 13 ).

10.3.3 Lateral stroke of Multi-pole Strip Magnets

The lateral movement range (stroke) is limited by the area at which all Hall sensors of the IC are covered by the

magnet in either direction. The Hall array on the AS5311 has a length of 2.0mm, hence the total stroke is

maximum lateral Stroke = Length of active area – length of Hall array

Note: active area in length is defined as the area containing poles with the specified 1.0mm pole length. Shorter

poles at either edge of the magnet must be excluded from the active area (see Figure 13).

Figure 13: Active Area of Strip Magnet

N

strip length

2mm

S

N

S

N

S

N

S

N

S

Active area (length)

Active Area

recommended

scanning path

B