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AS5130

Data Sheet - D e ta i l e d D e s c r i p t i o n

Magnetic Field Strength Indicators

The AS5130 is not only able to sense the angle of a rotating magnet, it can also measure the magnetic field strength

(and hence the vertical distance) of the magnet. This additional feature can be used for several purposes:

- as a safety feature by constantly monitoring the presence and proper vertical distance of the magnet

- as a state-of-health indicator, e.g. for a power-up self test

- as a pushbutton feature for rotate-and-push types of manual input devices

The magnetic field strength information is available in two forms – Magnetic field strength hardware indicator and

Magnetic field strength software indicator.

Magnetic Field Strength Hardware Indicator

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

AGC. If the AGC value is <3FH , the CAO output will be high (green range), If the AGC is at its upper limit (3FH), the

CAO output will be low (red range).

Magnetic Field Strength Software Indicator

D13:D7 in the serial data that is obtained by command READ ANGLE (see Table 8) contains the 6-bit AGC

information. 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 AS5130 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.

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 AS5130. Again, vertical distance variations can be compensated by the AGC.

The temperature and material of the magnet. The recommended magnet for the AS5130 is a diametrically mag-

netized 6mm diameter magnet. Other magnets may also be used as long as they can maintain to operate the

AS5130 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 tem-

perature is automatically compensated by the AGC.

OTP Sensitivity Adjustment

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

normal operating temperature should be in the middle between minimum and maximum, hence it should be around 32

(20H). To facilitate the “vertical centering” of the magnet+IC assembly, the sensitivity of the AS5130 can be adjusted in

the OTP register in 8 steps (see Table 9). The OTP sensitivity setting corresponds to the customer register setting gain

<2:0>.

“Pushbutton” Feature

Using the magnetic field strength software and hardware indicators described above, the AS5130 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 CAO 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.