AS5030_1 AMSCO [austriamicrosystems AG], AS5030_1 Datasheet - Page 25

• Manufacturer Part Number: AS5030_1
• Description: 8 BIT PROGRAMMABLE HIGH SPEED MAGNETIC ROTARY ENCODER
• Manufacturer: AMSCO [austriamicrosystems AG]

AS5030 8-bit Programmable Magnetic Rotary Encoder
9.2
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.
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,
If the magnet is too far away (or missing) or if the magnetic field is too weak, the AGC will be reading 63 (3F
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…
Rev. 1.8
64
56
48
40
32
24
16
8
0
Vertical distance of the magnet
0
sample#1
Figure 30: Typical curves for vertical distance versus ACG value on several untrimmed samples
500
sample#2
Linearity and AGC vs Airgap
1000
Airgap [mm]
www.austriamicrosystems.com
sample#3
[µm]
1500
sample#4
2000
Linearity [°]
2500
2,2
2,0
1,8
1,6
1,4
1,2
1,0
H
).
Page 25 of 33