AS5030 8-bit Programmable Magnetic Rotary Encoder

Rev. 1.8

www.austriamicrosystems.com

Page 19 of 33

The magnetic field strength information is available in two forms:

6.3.1

Magnetic Field Strength Hardware Indicator:

Pin MagRngn (#1) will be low, when the magnetic field is too weak. The switching limit is determined by the value of the AGC. If

output will be low (red range).

6.3.2

Magnetic Field Strength Software Indicator:

D13:D7 in the serial data that is obtained by command READ ANGLE (5.2.1) contains the 6-bit AGC information (see 5.2.1). The

AGC is an automatic gain control that adjusts the internal signal amplitude obtained from the Hall elements to a constant level.

If the magnetic field is weak, e.g. with a large vertical gap between magnet and IC, with a weak magnet or at elevated

temperatures of the magnet, the AGC value will be high. Likewise, the AGC value will be lower when the magnet is closer to the

IC, when strong magnets are used and at low temperatures.

The best performance of the AS5030 will be achieved when operating within the AGC range. It will still be operational outside

the AGC range, but with reduced performance especially with a weak magnetic field due to increased noise.

6.3.3

Factors Influencing the AGC Value

In practical use, the AGC value will depend on several factors:

•

the initial strength of the magnet. Aging magnets may show a reducing magnetic field over time which results in an

increase of the AGC value. The effect of this phenomenon is relatively small and can easily be compensated by the

AGC.

•

the vertical distance of the magnet. Depending on the mechanical setup and assembly tolerances, there will always be

some variation of the vertical distance between magnet and IC over the lifetime of the application using the AS5030.

Again, vertical distance variations can be compensated by the AGC

•

the temperature and material of the magnet. The recommended magnet for the AS5030 is a diametrically magnetized,

5-6mm diameter NdFeB (Neodymium-Iron-Boron) magnet. Other magnets may also be used as long as they can

maintain to operate the AS5030 within the AGC range.

Every magnet has a temperature dependence of the magnetic field strength. The temperature coefficient of a magnet

depends on the used material. At elevated temperatures, the magnetic field strength of a magnet is reduced, resulting

in an increase of the AGC value. At low temperatures, the magnetic field strength is increased, resulting in a decrease

of the AGC value.

The variation of magnetic field strength over temperature is automatically compensated by the AGC.

6.3.4

OTP Sensitivity Adjustment

To obtain best performance and tolerance against temperature or vertical distance fluctuations, the AGC value at normal

To facilitate the “vertical centering” of the magnet+IC assembly, the sensitivity of the AS5030 can be adjusted in the OTP

register in 4 steps. A sensitivity adjustment is recommended, when the AGC value at normal operation is close to its lower limit

6.4

“Pushbutton” Feature

Using the magnetic field strength software and hardware

indicators described above, the AS5030 provides a useful

method of detecting both rotation and vertical distance

simultaneously. This is especially useful in applications

implementing a rotate-and-push type of human interface (e.g. in

panel knobs and switches).

The MagRngn output is low, when the magnetic field is below

the low limit (weak or no magnet) and high when the magnetic

field is above the low limit (in-range or strong magnet).

A finer detection of a vertical distance change, for example

when only short vertical strokes are made by the pushbutton, is

achieved by memorizing the AGC value in normal operation and

triggering on a change from that nominal the AGC value to

detect a vertical movement.

Figure 24: Magnetic field strength indicator

AS5030

Micro

Controller

100n

CS

CLK

DIO

+5V

VDD

VSS

VSS

C2

VDD

VDD

13

11

10

12

15

C1

VSS

3

14

I/O

Output

Output

MagRngn

1

LED1

1k