Page 10 ams Datasheet
Document Feedback [v2-06] 2014-Oct-14
AS5055A − Detailed Description
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: 15Ω in series
and 4.7μF to ground as shown in Figure 10.
Alternatively, a filter: 33Ω + 2.2μF may be used. However with
this configuration, the minimum supply voltage is 3.15V.
Reading an Angle
Sending a READ ANGLE command through the SPI interface
automatically powers up the chip, drives INT/ high and starts
another angle measurement. The completion of the angle
measurement is indicated by driving the INT/ output low and
clearing the WOW flag in the error status register. The
microcontroller can respond to the interrupt by reading the
angle value from the AS5055A over the SPI interface. (See
Figure 11).
A READ ANGLE command must not be sent while a
measurement is being performed as indicated by INT/ driven
high or WOW = 1.
Reducing the Angle Jitter
The chip only performs a single angle measurement after a
READ ANGLE command is received, after which it returns to
low-power mode, so it is in normal operating mode for only a
very short time (t
PwrUp
).
The angle jitter can be reduced by averaging several angle
measurements in the microcontroller. For example, an
averaging of four samples reduces the jitter by 6dB (50%).
Operating Modes
After a READ ANGLE command is sent, the angle is measured
and internal calculations are started. During this time (normal
operating mode) the INT/ output is high until the device finishes
the calculations and a second READ ANGLE command may not
be sent.
After the INT/ output is driven low the device goes into
low-power mode. If the microcontroller doesn't monitor the
INT/ output a minimum guard time (t
readout
) must be inserted
before the next READ ANGLE command can be sent.
After startup the AS5055A has higher power consumption than
during low-power mode. When the POR cell is deactivated the
chip uses less current during low-power mode (see POR OFF
Register).
