IC-TW28 Datasheet, PDF (62/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Rev D2, Page 62/80
SIN/COS AMPLITUDE MONITOR
The iC-TW28 continuously monitors the amplitude of
t_√he sin/cos input signals by calculating the quantity
sin² + cos². In pin configuration mode, this value is
used to activate xIRQ if the input signal amplitude be-
comes less than 60% or more than 120% of its cali-
brated value. In serial configuration mode, the ampli-
tude monitor must be specifically configured and cali-
brated.
To configure the amplitude moni_√tor, enter a value
for the desired sin/cos amplitude sin² + cos² in the
SC_AMP_TARG register. During auto calibration,
the iC-TW28 adjusts the sin/cos analog and digital
gain values to provide this sin/cos level after analog-
to-digital conversion. The recommended value is
SC_AMP_TARG = 150 (0x96).
Next, enter values for the amplitude limits in the
SC_AMP_LOW and SC_AMP_HIGH registers. These
values should be the lowest and highest acceptable
sin/cos amplitudes respectively. For example, to set
the amplitude monitor limits at ±10% with an amplitude
target of 150, enter the following values:
SC_AMP_HIGH = 150 + 10% = 165
SC_AMP_LOW = 150 − 10% = 135
In operation, the scamp bit (bit 5) in the STAT_VAL and
STAT_LATCH registers is set whenever the measured
sin/cos amplitude, SC_AMP, is outside these limits:
135 > SC_AMP > 165
Configure the desired action to take when this condition
occurs using the scamp bit (bit 5) in the STAT_SEL,
STAT_IE, and STAT_HIZ registers.
Finally, calibrate the sin/cos amplitude to the target
value using auto calibration: activate the xCALIB pin
or send an auto calibrate sin/cos (0x21) or auto cali-
brate all (0x23) command. After calibration, verify that
SC_AMP = SC_AMP_TARG.
EXCESSIVE ERROR DETECTION
The iC-TW28 continuously calculates the residual off-
set, balance, and phase error of the corrected sin/cos
signals. These residues represent the uncorrected sig-
nal error in the sin and cos channels, and are typically
zero when auto adaption is used.
In applications where auto adaption cannot be used,
the error residue values allow sensor signal quality to
be monitored in a host processor or microcontroller.
Programmable threshold values allow activating xIRQ
should any of the residue values become excessive.
This excessive error condition is indicated by the res
bits (bit 7) in the STAT_VAL and STAT_LATCH regis-
ters.
To configure excessive error detection, enter values for
the four threshold (TH) registers. These values are the
maximum error residue that should be allowed during
operation.
In operation, STAT_VAL.res and STAT_LATCH.res
are set whenever the absolute value of one of the
residues exceeds its corresponding threshold. Specifi-
cally, whenever
|S_OFS_RES| > SC_OFS_TH
|C_OFS_RES| > SC_OFS_TH
|SC_BAL_RES| > SC_BAL_TH
Residue Register
S_OFS_RES
C_OFS_RES
SC_BAL_RES
SC_PH_RES
Z_PH_RES
STAT_VAL.res
Residue Threshold Register
SC_OFS_TH
SC_BAL_TH
SC_PH_TH
Z_PH_TH
Table 122: Correction Residue Threshold Exceeded
|SC_PH_RES| > SC_PH_TH
|Z_PH_RES| > Z_PH_TH
Configure the desired action to take when this condi-
tion occurs using the res bit (bit 7) in the STAT_SEL,
STAT_IE, and STAT_HIZ registers. Store all these val-
ues to the internal EEPROM using the write configura-
tion to EEPROM command (0x11).