UG-1047 EVAL-ADA4571-2 User Guide
Rev. 0 | Page 6 of 9
Vsin, Vcos, and VTEMP Raw Outputs
The Vsin, Vcos and VTEMP Raw Outputs graph shows all six
outputs from the ADA4571-2 dual-channel magnetic angle sensor
(see Figure 6).
Figure 6. Vsin, Vcos, and VTEMP Raw Outputs Graph
The blue and red waveforms indicate the V
SINx
and V
COSx
outputs, respectively, and the green waveform indicates the
VTEMP output. As the magnet is rotated above the ADA4571-2
the V
SINx
and V
COSx
outputs change while staying 90° out-of-
phase. The two channels report similar results that differ by the
relative rotation of the sensor die and the voltage offset
differences for the sine and cosine channels.
This plot shows the output waveforms sampled by the AD7266
ADC. The waveforms are plotted in 12-bit code. The AD7266
simultaneously samples V
SIN1
and V
COS1
then switches inputs to
sample V
SIN2
and V
COS2
. An internal reference of 2.5 V is subtracted
in the hardware as the readout of the ADC is in twos compliment.
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 or extra errors introduced from the
phase delay between the sampling of the individual channels.
Every 50 samples of the V
SIN1
, V
COS1
, V
SIN2
, and V
COS2
, the
AD7266 samples VTEMP1 and VTEMP2.
When powering the board through the USB connector attached
to the SDP-S controller board there is some variation in the supply
voltage of the ADA4571-2. Due to the readout of the AD7266 in
twos compliment form, with respect to the internal 2.5 V reference,
the offset of these waveforms are higher than the inherent offset
of the ADA4571-2. 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 running, the evaluation board constantly samples the
V
SIN1
,V
COS1
,V
SIN2,
and V
COS2
before sampling the VTEMP1 and
VTEMP2 channel every 50 iterations.
The interval between sampling is chosen by inputting different
values into the ms between samples field (see Figure 7). The
default is 10 ms. This is a delay set after information is
transferred from the AD7266.
The # samples to graph field sets the number of samples to save
and show in the graphs. The default is 200 samples.
Figure 7. Graphing Options Pane
Outputs and Calculated Values
Output and calculated values give the sensor information in
number format (see Figure 8). Again, the V
SINx
, V
COSx
, and
VTEMP outputs are in 12-bit twos compliment form with
respect to the 2.5 V internal reference of the AD7266 ADC.
Figure 8. Outputs and calculated values Pane for Channel 1 and Channel 2
A calculated angle value is also shown, given by the Arctan1
(Angle) and Arctan2 (Angle) function field, and a calculated
radius, given by the square root of the sum of squares for each
V
SINx
and V
COSx
channel in the Radius1 (Code) and Radius2
(Code) field.
Electrical Angle
The electrical angle plot gives the calculated Arctan1 (Angle)
and Arctan2 (Angle) values in a visual format seen in Figure 9.
As the magnetic field angle changes at the anisotropic magneto
resistive (AMR) sensors, the electrical angle changes. Both
channels give approximately the same information.
Figure 9. Electrical Angle
