IC-TW28 Datasheet, PDF (65/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Rev D2, Page 65/80
Z TEST MODE AND CALIBRATION
When a zero or index sensor is used, the Z channel
must be properly configured and calibrated to ensure
one and only one Z output pulse per input revolution,.
Configuration consists of setting the Z channel com-
parator threshold; calibration is performed automati-
cally using auto calibration. See Calibration Overview
on page 27 for more information.
In serial configuration mode, the Z channel comparator
threshold is set via ZERO0.threshold and the result-
ing internal Z gating window can be observed on the
B outputs in Z test mode. The width of the Z output
pulse is set via ZERO1.zwidth. In pin configuration
mode, the Z channel comparator threshold is fixed at
ZERO0.threshold = 10 (42% of the amplitude of the
ZERO input signal) and ZERO1.zwidth = 0 (Z output is
1 AB edge wide).
96
0
Calibrated
ZERO Input
– 96
Internal
Z Gating Window
Z
zthreshold
gatewidth
t1
t2
Available on B outputs
in Z Test Mode
zwidth
Figure 36: Z Calibration
To configure the Z channel in serial configuration mode,
enter values for ZERO0.threshold and ZERO1.zwidth
using the SPI port or the Encoder Link interface. The
recommended starting values are 10 and 0 respectively
– the same values used in pin configuration mode.
pin OUTA
Calibrate the Z channel by initiating auto calibration and
providing sin/cos and_pZ_inER_OO_Uin_Tp_Buts as explained in Cali-
bration Overview on page 27. During Z auto calibration,
the iC-TW28 tunes the Z offset (Z_OFSA_COR) and
gain (Z_GNA_COR) so that the calibrated ZERO input
signal (blue) spans 75% of the 8-bit Z channel ADC
range. This results in a digitized amplitude of 96 as
shown in Figure 36.
Auto Z calibration also tunes zphase (not shown) to cen-
ter the Z output pulse in the Z gating window such that
t₁ = t₂ as shown in Figure 36. This provides the widest
possible margin for changes in the width of the Z gating
window (gatewidth) during operation due to tempera-
ture and other operating conditions. See PHASE_LSB
on page 44 for more information on zphase. When
calibration is complete, terminate auto calibration as
explained in Calibration Overview on page 27.
As shown in Figure 36, the internal Z gating window is
high when the calibrated ZERO input signal is above
zthreshold and low otherwise.
zthreshold = 4 × ZERO0.threshold
The actual threshold in percent of the amplitude of the
ZERO signal is
4 × ZERO0.threshold
× 100%
96
Thus, if ZERO0.threshold = 10, zthreshold = 40 and the
actual Z threshold is at 42% of the ZERO signal.