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iC-TW29
26-BIT ENCODER PROCESSOR
WITH INTERPOLATION AND BiSS INTERFACE
Rev C1, Page 18/28
When the AB output frequency is being limited, the AB
outputs 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the limiter is no longer active.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-TW29
stops operating. The AB output frequency limiter can
also be programmed to activate xIRQ.
3-phase UVW outputs for commutation of brushless
motors with up to 64 poles (32 pole pairs) per revolution
are also available as RS-422 compatible differential or
single-ended signals depending on device configura-
tion.
A BiSS Slave interface provides BiSS C-Mode bidirec-
tional communication of output angle (with indepen-
dently programmable resolution), revolution count, and
configuration data. Encoder Profiles 3, 3S (Safety), and
4 are implemented in the iC-TW29 or a custom profile
may be defined using a host processor. BiSS com-
mand requests are handled directly by the iC-TW29 for
stand-alone applications or can be passed through to
an external microprocessor via the SPI port in hosted
applications.
The BiSS interface can be configured to implement
BiSS Standard Encoder Electronic Data Sheet (EDS)
SE. This allows the BiSS master to read the encoder
configuration over the BiSS interface at startup. In
hosted applications, the host processor can implement
any BiSS EDS.
UVW scan mode allows external UVW signals to be
read by the iC-TW29 and sent to the BiSS master with
the BiSS single cycle data (BP4 or custom encoder pro-
file only). This allows commutation of a brushless motor
over BiSS before absolute position is synchronized.
The absolute data interface (ADI) is a BiSS/SSI master
for reading revolution and cycle count information from
an external absolute position system (such as iC-PVL).
Up to four synchronization bits can be used.
The I/O multiplexer determines which signals are trans-
ferred to the output pins. One of 23 output modes
(combinations of output types) can be selected. Up to
two different output types may be used simultaneously.
The SPI port is available for use by an external host
processor for initial calibration or general communica-
tion.
The iC-TW29 provides comprehensive monitoring func-
tions for status and faults, chip temperature and sin/cos
input signal quality.
The status/fault monitor monitors 16 internal conditions,
each of which can be individually configured to activate
a fault output to notify an external system during opera-
tion. The fault output is the active-low interrupt request
output (xIRQ) pin. In stand-alone applications, xIRQ
can be used to directly drive a fault LED. In hosted
applications, xIRQ is typically used to interrupt the host
when a fault occurs. In addition, real-time status and
fault information is available over the SPI and BiSS
interfaces.
The iC-TW29 incorporates an on-chip temperature sen-
sor. The temperature monitor can provide real-time
chip temperature data to a host processor or BiSS mas-
ter. The temperature monitor can be configured to
activate a status bit when chip temperature exceeds a
programmable limit. This condition can also activate
xIRQ.
The sin/cos amplitude monitor continuously monitors
the amplitude of the sin/cos input signals by calculating
the quantity
√
sin
2
+
cos
2
. If the input amplitude is out-
side configured limits, a status bit is activated and an
interrupt can be generated.
The excessive error monitor continuously calculates
the residual offset, balance, and phase error of the cor-
rected sin/cos signals. These residues represent the
uncorrected signal error of the sin and cos channels,
and are typically zero (or near zero) when auto adaption
is used. If any of the error residues exceeds configured
limits, a status bit is set and an interrupt can be gen-
erated. In applications where auto adaption cannot be
used, the residues allow sensor signal quality to be
monitored by a host processor.
The excessive adaption monitor continuously compares
the current offset, balance, and phase correction pa-
rameter values to baseline values store in the EEPROM
during device configuration. If any of the correction val-
ues deviate from the base values (due to auto adaption)
by more than the configured limits, a status bit is set
and an interrupt can be generated.
Auto calibration is used at initial device commissioning
to automatically determine gain, offset, channel bal-
ance, and phase compensation values for the sin, cos,
and zero channels. Auto calibration is initiated using
the xCALIB input pin or via a serial command. Cali-
brated values can be stored in the internal EEPROM
for use on subsequent startups.
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 and lowest jitter under all operating
conditions.
