IC-TW28 Datasheet, PDF (17/80 Pages) IC-Haus GmbH – 10-BIT SIN/COS INTERPOLATOR

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Rev D2, Page 17/80
Fault Handling
The iC-TW28 provides comprehensive fault handling
features and a fault output to notify external systems of
faults and warnings during operation. The fault output
is the active-low interrupt request output (xIRQ) pin (pin
16). In stand-alone applications, xIRQ can be used to
directly drive a fault LED. When the iC-TW28 is used
with a host processor or microcontroller, xIRQ is typi-
cally used to interrupt the host when a fault occurs. In
Serial configuration mode, real-time status and fault
information is available over the SPI port.
In pin configuration mode, xIRQ is activated if there
is an internal fault in the signal path or if the sensor
input amplitude becomes less than 60% or more than
120% of its calibrated value. In Serial configuration
mode, additional status conditions (signal path satu-
ration/overflow, excessive input frequency, excessive
AB output frequency, excessive adaption, and exces-
sive position lag) can be monitored and programmed
to activate xIRQ.
AB Output Frequency Limiter
The iC-TW28 incorporates a programmable AB output
frequency limiter that guarantees a minimum separa-
tion time between AB edges. This is useful to avoid
counting errors with PLCs or counters with input fre-
quency limits less than the 12.5 MHz maximum output
frequency of the iC-TW28. Six output frequency limit
choices are available in pin configuration mode; Serial
configuration mode provides 256 choices.
When AB output frequency is being limited, the AB out-
puts lag behind the sin/cos inputs. If this condition is
temporary or transient, the AB outputs catch up when
the limiter is no longer active. If this condition persists,
however, a fatal fault is generated and the iC-TW28
stops working. In Serial configuration mode, the AB
output frequency limiter can be programmed to activate
xIRQ.
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, other ampli-
tude limits can be set.
LED Intensity Control (Serial Only)
In serial configuration mode, the calculated sin/cos am-
plitude value can also be used to drive the LED output
(pin 26) to control the intensity of an optical sensor LED.
This maintains the sin/cos signals at their calibrated
amplitude in the presence of LED ageing and varying
application conditions.
Multi-Cycle Counter (Serial Only)
A 14-bit multi-cycle counter is available in the iC-TW28
to track up to 16,383 input cycles during operation. In
serial configuration mode, the multi-cycle counter can
be read and written using commands and can be con-
figured to reset on the rising edge of the Z output. The
multi-cycle counter value can only be read using the
SPI port.
Should input cycle counting beyond the range of the
built-in multi-cycle counter be required, the iC-TW28
can be configured to generate an interrupt (activate
xIRQ) when there is an imminent overflow of the mul-
ti-cycle counter. In this way, a host processor or mi-
crocontroller can extend the counter to any arbitrary
length.
Position Capture (Serial Only)
The full 24-bit position value (10 bits of interpolated
angle within an input cycle plus 14 bits of multi-cycle
count) of the iC-TW28 can be captured and read out
over the SPI port. This capture can be configured to
take place on the rising edge of the Z output or the
ZERO input gating window and can also be configured
to generate an interrupt. This allows touch-probe or
distance-coded index applications to be easily imple-
mented using the iC-TW28.
Filter Adaption (Serial Only)
In serial configuration mode, the signal path filter can be
configured to dynamically adjust its bandwidth based
on sensor input acceleration. This allows heavy filter-
ing to be used to provide a smooth output at constant
speed while still maintaining fast response to changes
in input conditions.
Residual Error Calculation (Serial Only)
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, these residual values
allow sensor signal quality to be monitored in a host
processor or microcontroller. Programmable threshold
values allow activating xIRQ should any of the residual
values become excessive.
EEPROM
The iC-TW28 provides an internal EEPROM to store
configuration and initial calibration data for use at
startup. In addition to a standard checksum on the
EEPROM data, sophisticated data encoding allows de-
tecting and correcting single-bit errors and detecting
two-bit errors for enhanced application protection. The
EEPROM is usually locked (write protected), but can
be unlocked via serial command.