IC-TW28 Datasheet, PDF (16/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Digital Error Correction
After digital conversion, the sin/cos signals are pro-
cessed to remove any remaining offset, equalize signal
amplitude, and ensure exact 90^◦ shift. Correcting these
signal errors increases interpolation accuracy for lowest
error and jitter. Initial error correction values are deter-
mined automatically by auto calibration during initial
system calibration. During operation, these correction
values are monitored and automatically adjusted (au-
to-adaption) to provide high accuracy signals under
changing application conditions.
Angle Calculation (Arctan)
The angle within an input cycle indicated by the con-
ditioned digital sin/cos signals is next calculated as
arctan(Sin/Cos) with a resolution of 10 bits using a
CORDIC algorithm.
Filter
A configurable filter is provided in the signal path to re-
duce noise and jitter in the AB and UVW outputs. In pin
configuration mode, three filter settings (light, medium,
and heavy) are available. In Serial configuration mode,
additional control over the signal path filter’s character-
istics is available.
Hysteresis
Hysteresis is available in the AB and UVW signal paths
to reduce output dithering (instability) at standstill at
the expense of position error on direction reversal. In
pin configuration mode, four hysteresis settings are
available; Serial configuration mode expands this to 32
settings.
the Z signal path to generate a programmable-width Z
output synchronized with the AB outputs.
Automatic phase correction to center the Z output pulse
location within the ZERO input gating window is pro-
vided. This Z phase correction value is determined
automatically using auto calibration during initial sys-
tem calibration.
Post-AB Divider
An optional programmable divider after the ABZ gener-
ator is available. This provides fractional or non-integer
AB output resolutions and interpolation factors for spe-
cial applications.
UVW Signal Path
In addition to the ABZ outputs, the iC-TW28 can gen-
erate 3-phase UVW outputs for commutating brush-
less motors with up to 64 poles (32 pole pairs). Pro-
grammable phase correction to properly align the UVW
signals with the motor and hysteresis to reduce signal
noise (jitter) at standstill are provided.
ABZ/UVW Outputs
The iC-TW28 contains a built-in RS422 compatible dif-
ferential line driver for driving 120 Ω terminated cables.
In Serial configuration mode, the line driver can be by-
passed to save power in imbedded or short signal-run
applications. Differential ABZ or UVW outputs or si-
multaneous single-ended ABZ and UVW outputs are
available.
Interpolation Factor
The 10-bit sensor input angle value is scaled to the
resolution required by the desired interpolation factor.
In pin configuration mode, 24 interpolation factors (12
each binary and decimal) are available. In Serial config-
uration mode, interpolation factors between 2 and 256
may be selected.
Auto Calibration
Auto calibration is used at initial calibration to auto-
matically determine initial offset, gain, and phase com-
pensation values for the sin, cos, and zero channels.
Activating the xCALIB input (pin 15) or sending a serial
command initiates auto calibration; deactivating xCALIB
or a serial command stores the calibrated values to the
internal EEPROM.
Z Signal Path
The Z signal path is similar to the sin/cos signal path.
Analog offset and gain correction are provided to condi-
tion the zero signal. Correction values are determined
using auto calibration during initial system calibration.
An 8-bit ADC and configurable comparator are used to
generate the Z gating window. The Z gating window al-
lows producing one and only one Z pulse per revolution
in applications where there are multiple input cycles per
revolution.
ABZ Generator
The AB generator synthesizes quadrature AB outputs
at the interpolated resolution. The output generator
also uses the conditioned Z gating window signal from
In pin configuration mode, it is possible to eliminate cali-
bration entirely by permanently grounding xCALIB. This
permanently enables auto calibration, and the iC-TW28
will calibrate itself at every startup. In this way, no ini-
tial calibration is required, greatly simplifying product
manufacturing and deployment.
Auto Adaption
Auto adaption maintains optimal offset, channel bal-
ance, and phase compensation values for the sin and
cos channels during operation to ensure maximum in-
terpolator accuracy under all operating conditions. In
serial configuration mode, auto adaption can be dis-
abled.