as5134 austriamicrosystems, as5134 Datasheet - Page 18

• Manufacturer Part Number: as5134
• Description: 360?programmable High Speed Bldc Magnetic Rotary Encoder
• Manufacturer: austriamicrosystems

AS5134
Data Sheet - D e t a 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:
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:
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.
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- 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 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.
011111111
00000011
Bit Code
01111111
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Revision 1.6
Decimal Value
256
127
+3
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