as5055 austriamicrosystems, as5055 Datasheet - Page 6

• Manufacturer Part Number: as5055
• Description: Low Power 12 Bit Magnetic Rotary Encoder
• Manufacturer: austriamicrosystems

AS5055
Data Sheet – Operation Modes
9 Operation Modes
9.1 Typical Application
The AS5055 requires only a few external components in order to operate immediately when connected to the host
microcontroller. Only 6 wires are needed for a simple application using a single power supply: two wires for power and
four wires for the SPI communication. A seventh connection can be added in order to send an interrupt to the host
CPU to inform that a new valid angle can be read.
Figure 3. Typical Application Using SPI 4-Wire Mode and INT/ Output
Upon power-up, the AS5055 performs a full power-up sequence including one angle measurement. The completion of
this cycle is indicated at the INT/ output pin and the angle value is stored in an internal register. Once this output is
set, the AS5055 suspends to sleep mode.
9.2 Power Supply Filter
Due to the sequential internal sampling of the Hall sensors, fluctuations on the analog power supply (pin#12: VDD)
may cause additional jitter of the measured angle. This jitter can be avoided by providing a stable VDD supply. The
easiest way to achieve that is to add a RC filter: 15
+ 4.7µF in the power supply line as shown in Figure 3.
Alternatively, a filter: 33
+ 2.2µF may be used. However with this configuration, the minimum supply voltage is 3.15V.
9.3 Reading an Angle
The external microcontroller can respond to the INT request by reading the angle value from the AS5055 over the SPI
interface. Once the angle value is read, the INT output is cleared again.
Sending a “read angle” command by the SPI interface also automatically powers up the chip and starts another angle
measurement. As soon ad the microcontroller has completed reading of the angle value, the INT output is cleared and
a new result is stored in the angle register. The completion of the angle measurement is again indicated by setting the
INT output and a corresponding flag in the status register.
9.3.1
Reducing the Angle Jitter
Due to the measurement principle of the chip, only a single angle measurement is performed in very short time
(~600µs) after each power-up sequence. As soon as the measurement of one angle is completed, the chip suspends
to power-down state. An on-chip filtering of the angle value by digital averaging is not implemented, as this would
require more than one angle measurement and consequently, a longer power- up time which is not desired in low-
power applications.
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