AS5030 8-bit Programmable Magnetic Rotary Encoder

Rev. 1.8

www.austriamicrosystems.com

Page 25 of 33

9.2

Vertical distance of the magnet

The chip-internal automatic gain control (AGC) regulates the input signal amplitude for the tracking-ADC to a constant value.

This improves the accuracy of the encoder and enhances the tolerance for the vertical distance of the magnet.

Linearity and AGC vs Airgap

0

8

16

24

32

40

48

56

64

0

500

1000

1500

2000

2500

Airgap [mm]

1,0

1,2

1,4

1,6

1,8

2,0

2,2

sample#1

sample#2

sample#3

sample#4

Linearity [°]

Figure 30: Typical curves for vertical distance versus ACG value on several untrimmed samples

As shown in Figure 30, the AGC value (left Y-axis) increases with vertical distance of the magnet.

Consequently, it is a good indicator for determining the vertical position of the magnet, for example as a pushbutton feature, as

an indicator for a defective magnet or as a preventive warning (e.g. for wear on a ball bearing etc.) when the nominal AGC

value drifts away.

If the magnet is too close or the magnetic field is too strong, the AGC will be reading 0,

The AS5030 will still operate outside the AGC range, but the accuracy may be reduced as the signal amplitude can no longer be

kept at a constant level.

The linearity curve in Figure 30 (right Y-axis) shows that the accuracy of theAS5030 is best within the AGC range, even slightly

better at small airgaps (0.4mm ~ 0.8mm).

At very short distances (0mm ~ 0.1mm) the accuracy is reduced, mainly due to nonlinearities in the magnetic field.

At larger distances, outside the AGC range (~2.0mm ~ 2.5mm and more) the accuracy is still very good, only slightly decreased

from the nominal accuracy.

Since the field strength of a magnet changes with temperature, the AGC will also change when the temperature of the magnet

changes. At low temperatures, the magnetic field will be stronger and the AGC value will decrease. At elevated temperatures,

the magnetic field will be weaker and the AGC value will increase.

Sensitivity trimming

As the curves for the 4 samples in Figure 30 show, the AGC value will not show exactly the same value at a given airgap on

each part. For example, at 1mm vertical distance, the AGC may read a value between ~11 ~ 24. This is because for normal

operation an exact trimming is not required since the AGC is part of a closed loop system.

However, the AS5030 offers an optional user trimming in the OTP (see 5.2.4) to allow an even tighter AGC tolerance for

applications where the information about magnetic field strength is also utilized, e.g. for rotate-and-push types of knobs, etc…

[µm]