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AS5134

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 AS5134 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 Software Indicator

The serial data that is obtained by command READ ANGLE 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 AS5134 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 AS5134. Again, vertical distance variations can be compensated by the AGC.

The temperature and material of the magnet. The recommended magnet for the AS5134 is a diametrically mag-

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

they can maintain to operate the AS5134 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.

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

100000 (20H). To facilitate the “vertical centering” of the magnet+IC assembly, the sensitivity of the AS5134 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 (around 00H). The default sensitivity setting is 00H = high sensitivity. Any value

>00H will reduce the sensitivity.

Multi Turn Counter

A 9-bit register is used for counting the magnet’s revolutions. With each zero transition in any direction, the output of a

special counter is incremented or decremented. The initial value after reset is 0 LSB. The multi turn value is encoded

as complement on two. Clockwise rotation gives increasing angle values and positive turn count. Counter clockwise

rotation exhibits decreasing angle values and a negative turn count respectively.

Bit Code

Decimal Value

011111111

256

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01111111

127

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00000011

+3