Analog Devices EV-ADA4571RSDZ, User Manual

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UG-1169 EV-ADA4571RSDZ User Guide
Rev. 0 | Page 6 of 9
V
SIN
, V
COS
, and VTEMP Raw Outputs
The Vsin, Vcos and VTEMP Raw Outputs graph shows the
three outputs from the ADA4571 magnetic angle sensor (see
Figure 6).
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Figure 6. Vsin, Vcos, and VTEMP Raw Outputs Graph
In Figure 6, the blue and red waveforms indicate the V
SIN
channel
and V
COS
channel outputs, respectively, and the green waveform
indicates the VTEMP channel output. As the magnet rotates
above the
ADA4571 , the V
SIN
and V
COS
outputs change while
staying 90° out of phase. These two channels ,V
COS
and V
SIN
,
report similar results that differ by the relative rotation of the
sensor die and the voltage offset differences for the sine and
cosine channels.
Figure 6 shows the output waveforms sampled by the AD7866
ADC. The waveforms are plotted in 12-bit code. The AD7866
simultaneously samples V
SIN
and V
COS
. An internal reference of
2.5 V is subtracted in the hardware because the readout of the ADC
is in twos complement. Therefore, the two signals center around
0 in the raw waveform plot. In a real application, it is important
that these two channels are simultaneously sampled because
extra errors can be introduced from the phase delay between
the sampling of the individual channels. For every 50 samples of
the V
SIN
and V
COS
, the AD7866 samples the VTEMP channel.
When powering the EV-ADA4571RSDZ evaluation board through
the USB connector attached to the
SDP-S controller board, some
variation appears in the supply voltage of the ADA4571 .
Because the readout of the AD7866 is in twos complement
format, with respect to the internal 2.5 V reference, the offset of
these waveforms is higher than the inherent offset of the
ADA4571 . After offset correction of the sine and cosine signals,
which is recommended for the end use of the sensor, the offsets
due to the ADC reference, as well as the sensor offset, are
removed.
Graphing Options
When the EV-ADA4571RSDZ evaluation board is operating, it
constantly samples the V
SIN
channel and V
COS
channel, and it
samples the VTEMP channel after every 50 samples of the V
SIN
and the V
COS
channels.
To choose the interval between samples, enter different values
in the
ms between samples text box (see Figure 7). The default
interval is 10 ms. This delay is set after information is transferred
from the
AD7866 .
The # samples to Graph field sets the number of samples to
save and display in the graphs. The default number of samples
saved and displayed is 200 samples.
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Figure 7. Graphing Options Pane
Outputs and Calculated Values
The values shown in the Output and calculated values pane
show the ADA4571 output information in number format (see
Figure 8). Again, the V
SIN
, V
COS
, and VTEMP outputs are in
12-bit, twos complement format with respect to the 2.5 V
internal reference of the
AD7866 ADC.
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Figure 8. Outputs and calculated values Pane
A calculated angle value is also shown in Figure 8, given by the
Arctangent2 (Angle)
function field, and a calculated radius,
given by the square root of the sum of squares for V
SIN
channel
and V
COS
channel in the Radius (Code) field.
Electrical Angle
The electrical angle plot gives the calculated Arctangent2 (Angle)
value in a visual format, as shown in Figure 9. As the magnetic
field angle changes at the anisotropic magneto resistive (AMR)
sensors, the electrical angle changes.
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Figure 9. Electrical Angle Plot