IC-TW28 Datasheet, PDF (25/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Rev D2, Page 25/80
The amount of filtering is a compromise between fast
response and smoothness of the AB outputs. It is rec-
ommended to start with light filtering since this gives
the fastest response of the AB outputs to changes in
the sin/cos inputs. Medium or heavy filtering may be se-
lected if the outputs are noisy or jittery. Experimentation
may be necessary to determine the optimal setting.
Where Interpolation is the interpolation factor set using
configuration inputs C0 and C3.
For example, if an interpolation factor of 250 is selected
using C0 and C3, and C2 is at configuration level 8
(1.56 MHz), the maximum AB frequency will be reached
at a sensor input frequency of
AB Frequency Limit and Auto Adaption
Configuration input C2 is used to set the AB frequency
limit (minimum AB edge separation) and to enable or
disable auto adaption. Choose the desired configura-
tion from Table 10 and connect the appropriate resistors
to configuration input C2 according to Table 7 to set the
corresponding configuration level.
C2
Level
11
10
9
8
7
6
5
4
3
2
1
0
Max. AB
Frequency
195 kHz
390 kHz
781 kHz
1.56 MHz
3.12 MHz
6.25 MHz
195 kHz
390 kHz
781 kHz
1.56 MHz
3.12 MHz
6.25 MHz
Min. Edge
Separation
1.28 µs
640 ns
320 ns
160 ns
80 ns
40 ns
1.28 µs
640 ns
320 ns
160 ns
80 ns
40 ns
Auto
Adaption
On
Off
Table 10: Configuration Input C2
1.56 MHz
finput = ₂₅₀ = 0.00624 MHz = 6.24 kHz
If the sin/cos sensor input exceeds this frequency, the
AB output position can no longer keep up with the sen-
sor position. In this case, the iC-TW28 keeps gener-
ating output pulses at the maximum AB frequency. If
this condition is temporary or transient, the AB outputs
catch up when the sin/cos input frequency decreases.
If this condition persists, however, a fatal fault is gener-
ated and the iC-TW28 stops working.
Input Range, Interpolation Group, and Z Calibra-
tion
Configuration input C3 selects the input signal range,
the interpolation group, and whether Z channel auto
calibration is used. Choose the desired setting from
Table 11 and connect the appropriate resistors to con-
figuration input C3 according to Table 7 to set the corre-
sponding configuration level.
The highest maximum AB output frequency in pin con-
figuration mode is 6.25 MHz, which is equivalent to an
edge separation of 40 ns. Lower maximum output fre-
quencies (higher minimum edge separation) can be
selected as shown in Table 10 if devices connected
to the iC-TW28 (counters, PLCs, motion controllers,
drives, etc.) cannot handle its full output frequency.
Auto adaption maintains optimal offset, channel bal-
ance, and phase compensation values for the sin and
cos channels during operation to ensure maximum inter-
polator accuracy under all operating conditions. Unless
specifically required otherwise, it is recommended to
enable auto adaption and to use the highest maximum
AB frequency (configuration level 6).
The sin/cos sensor input frequency (finput) that corre-
sponds to a given AB output frequency can be calcu-
lated using the following formula:
C3
Level
11
10
9
8
7
6
5
4
3
2
1
0
Input
Range
Reserved
High
Low
Reserved
High
Low
Reserved
High
Low
Reserved
High
Low
Interpolation Auto Z
Group
Calibration
I1
Yes
I0
I1
No
I0
Table 11: Configuration Input C3
Select low input range for MR or Hall effect sensors pro-
ducing differential outputs of up to ±700 mV peak. Se-
lect high input range for GMR, TMR, or optical sensors
with outputs of up to ±2 V peak. See Input Configura-
tion and Signal Levels on page 55 for more information.
Do not select a reserved input range.
finput = ^ABFrequency
Interpolation
Select the interpolation group corresponding to the de-
sired interpolation chosen using configuration input C0.