IC-TW28 Datasheet, PDF (27/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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CALIBRATION OVERVIEW
Once the iC-TW28 has been configured, the sin and
cos channels must be calibrated to determine proper
values for gain, offset correction, channel balance, and
phase correction. This is most easily done using the
auto calibration feature of the iC-TW28 to automatically
determine optimum values for these parameters. If the
ZERO inputs are used, the Z channel must also be
calibrated for gain, offset correction, and phase. Auto
calibration is also available for the Z channel.
Auto calibration can be initiated in hardware using the
xCALIB input or via software commands using the SPI
port or the Encoder Link interface. With auto calibration
initiated, provide sensor input of a few hundred sin/cos
cycles and the iC-TW28 tunes the correction parame-
ters to provide lowest error and jitter in the interpolated
AB and/or UVW outputs. Z channel auto calibration can
be accomplished along with AB/UVW auto calibration
or separately.
Hardware Auto Calibration (xCALIB)
Hardware auto calibration can be used in both pin and
serial configuration modes and is initiated by pulling
the xCALIB input low. A push-button switch and pull-up
resistor connected between xCALIB (as shown in Fig-
ure 10 on page 18) is an easy way to achieve this in
series production. Auto calibration can also tune the Z
channel. In pin configuration mode, this is controlled
by configuration input C3. In serial configuration mode,
auto calibration can be configured to tune or not tune
the Z channel and to automatically store or not store
the calibrated parameters to EEPROM when xCALIB is
released.
The recommended sequence for hardware auto calibra-
tion in pin configuration mode is:
1. Pull xCALIB input low.
The sensor input used for auto calibration does not
need to be at a constant frequency nor must it be unidi-
rectional. A rotary encoder can be calibrated by moving
the disc or wheel back and forth by a few revolutions; a
linear encoder by moving the sensor back and forth on
the scale by a few centimeters. If Z auto calibration is
used, input motion must include generation of a ZERO
input signal.
After providing sufficient input signals, auto calibration
is terminated using the xCALIB input or software com-
mands and the tuned correction values are stored to
the internal EEPROM for use on subsequent startups.
2. Provide sensor input signals as explained in Cali-
bration Overview.
3. Release the xCALIB input (it is pulled high by the
external pull-up resistor) to store all calibrated
values to the EEPROM.
The recommended sequence for hardware auto calibra-
tion in serial configuration mode is:
1. Ensure all static (configuration) registers have
valid values for the desired application, espe-
cially SC_AMP_TARG (the recommended value
is 150).
2. Pull xCALIB input low.
3. Provide sensor input signals as explained in Cali-
bration Overview.
4. Release the xCALIB input (it is pulled
high by the external pull-up resistor). If
ADAPT_CFG1.xcalee = 1, the calibrated values
are automatically stored to the EEPROM.
5. If ADAPT_CFG1.xcalee = 0, store the calibrated
COR register values to the BASE registers by
writing 0x12 to the COMMAND register. Then
store the calibrated COR and BASE register val-
ues to the internal EEPROM by writing 0x11 to
the COMMAND register.