IC-TW28 Datasheet, PDF (70/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

W^iCIT^-H^TA^WU²TO⁸-C1A0L-BIBITRSATINIO/CNOASNINDTLEINREPODLRAIVTp^{OERrReliminary}
Rev D2, Page 70/80
FILTER CONFIGURATION
The signal path filter is used to reduce noise and jitter
in the AB and UVW outputs and the position value read
via the SPI port. It can also reduce angle lag at constant
speed due to interpolator latency. In pin configuration
mode, three filter settings (light, medium, and heavy)
are available. In serial configuration mode, the filter
must be configured.
The filter is implemented as a PI servo loop with op-
tional feedback path delay as shown below.
lag at constant input velocity due to interpolator latency
is reduced by 40% when MAIN_CFG.noise = 0 and by
22% when MAIN_CFG.noise = 1. Note that when feed-
back delay is used (FILT_CFG.fb = 1), FILT_K.kp ≥ 3
is required, otherwise the filter may become unstable.
FILT_CFG.auto determines whether the P gain of
the filter is static or dynamic. The normal setting is
FILT_CFG.auto = 0, in which case the P gain of the
filter loop is static and as set by FILT_K.kp.
Filter
Input
FILT_CFG.auto
Filter Lag
-
FILT_K.kp
FILT_K.ki
FILT_CFG.fb
640 ns
Delay
In general, filter configuration is a compromise between
fast response to sensor input changes and smoothness
Filter
of the outputs. It is recommended to start with maxi-
Output
mum filter bandwidth (least filtering) since this gives the
fastest response of the outputs to changes in the sin/-
cos inputs. Filtering can then be increased as required
to reduce output noise and jitter. Experimentation may
be necessary to determine the optimal configuration.
Figure 39: Signal Path Filter
To configure the signal path filter for fastest response
(least filtering), use the settings shown below.
FILT_K.kp determines the proportional (P) gain of the
loop, which sets the noise and jitter bandwidth of the
filter. Lower FILT_K.kp v_pa_gal_iu_n es pro_iv_gai_id_n e higher P gain
and higher filter bandwidth (less filtering). Higher val-
ues provide more filtering and less output ¹noise and
jitter.
From LUT
s
14
- ^{FILT_K.ki determines the integral (I) gain of the loop,}
which affects the amount of filter lag under acceler-
ation. Any non-zero FILT_K.ki value aDlseolayprovides
zero filter lag at constant sensor input velocity. Lower
FILT_K^p.^gk^aiⁱⁿvalue^igasⁱⁿprovide higher I gain and less filter lag
under acceleration. H₁owever, lower FILT_^deK^la.^yki values
can also produce pos_sition overshoot on deceleration.
FILT_K.ki = 3 is the recommended₁ value.
-^s
Note that FILT_K.kp = 0 with FILT_K.ki = 1 is unstable
and thereforepgsaihn ould not be used. Also, if FILT_K.ki =
0, FILT_K.kp must also be 0.
1
- ^{FILT_CFG.fb determisnes whether or not the loop feed-}
back path includes the 640 ns delay or not. This delay
is used to reduce the position lag at constant sensor
input velocity due to interpolator latency. The intrinsic
interpolator latency of the iC-TW28 depends on the
value of MAIN_CFG.noise. If FILT_CFG.fb = 1, position
Fastest Response Filter Configuration
Parameter
Value Description
FILT_K.kp
0
Maximum P gain
FILT_K.ki
3
Nominal I gain
FILT_CFG.fb 0
No feedback path delay
FILT_CFG.auto 0
To Hysteresis
Static filter kp
1
16
s Table 125: Fastest Response Filter Configuration
Increase FILT_K.kp as required to reduce output
noise and jitter. Enable the feedback path delay
(FILT_CFG.fb = 1) as required to reduce the position
lag at constant sensor input velocity due to interpolator
latency.
The recommended filter configurations that correspond
to light, medium, and heavy filtering in pin configuration
mode are shown below.
Filtering
Light
Medium
Heavy
Recommended Filter Configurations
FILT_K.kp FILT_K.ki FILT_K.fb FILT_K.auto
2
3
0
0
4
3
0
0
6
3
0
0
Table 126: Recommended Filter Configurations