TW8 datasheet(2/63 Pages) ICHAUS

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iC-TW8 16-BIT SIN/COS INTERPOLATOR

WITH AUTO-CALIBRATION

Rev A2, Page 2/12

DESCRIPTION

The iC-TW8 is a 16-bit application-speciﬁc DSP inter-

polator for sine/cosine signals with automatic calibra-

tion and adaption of signal path parameters during

operation to maintain minimum angular error and jit-

ter. Angular position is calculated at a programmable

resolution of up to 65,536 increments per input cy-

cle. Automatic calibration and adaption (correction

during operation) of sensor offset, Sin/Cos amplitude

match, and phase quadrature is provided. Addition-

ally, a 64-byte lookup table (LUT) is available to cor-

rect for residual harmonic distortion in the sensor sig-

nals.

The iC-TW8 accepts 10 mV to 700 mV differential

Sin/Cos input signals directly from magnetic or op-

tical sensors – no external signal conditioning is re-

quired in most applications. The differential zero (ref-

erence) input accepts a wide range of digital and ana-

log index gating sources such as Hall or MR sen-

sor bridges. The Z output width, position relative to

the Sin/Cos inputs, and synchronization to the AB

quadrature outputs is fully programmable.

In addition to industry-standard incremental ABZ

quadrature output, the iC-TW8 provides optional

PWM (potentiometer) and serial-only (SPI or 1-wire)

output modes for special or imbedded applications.

The incremental ABZ quadrature output can be gen-

erated at a frequency of up to 8 MHz (31 ns edge

spacing); the maximum output frequency can also be

limited so as not to overwhelm connected counters.

In PWM output mode, the iC-TW8 provides a differ-

ential pulse-width modulated signal proportional to

the calculated angle (position) of the Sin/Cos inputs.

An RC ﬁlter may be used to provide an analog volt-

age output for potentiometer applications, or to drive

an external ADC for simple single-turn absolute ap-

plications. Synchronous digital ﬁlters may be imple-

mented using an external microcontroller or FPGA

for more sophisticated or imbedded applications.

In serial-only output mode, the iC-TW8’s internal 32-

bit position counter and instantaneous angular veloc-

ity register can be read via the built-in SPI or 1-wire

serial ports at clock rates of up to 32 MHz. Higher in-

put signal frequencies are allowed in serial-only out-

put mode since the ABZ output frequency limitation

is not applicable.

The iC-TW8 offers two conﬁguration modes.

conﬁguration mode provides simple, static conﬁgura-

tion that does not require any programming or com-

plicated calibration. Pin conﬁguration mode uses a

subset of the iC-TW8’s complete capabilities includ-

ing ABZ quadrature output, a limited choice of the

most commonly used interpolation (resolution) and

hysteresis values, and one-button calibration. Eight

resistors set voltage levels at four conﬁguration input

pins to select all operating parameters, simplifying

product assembly. One-button auto calibration sets

input gain and compensates sensor offset and Sin/-

Cos channel gain match and phase with just a few

input cycles and then stores the compensation val-

ues to EEPROM.

In more sophisticated applications, serial conﬁg-

uration mode allows access to all iC-TW8 fea-

tures. Complete device conﬁguration using the bi-

directional SPI or 1-wire serial ports provides ac-

cess to all resolutions (including fractional interpola-

tion), the sensor distortion LUT, fully programmable

hysteresis, and advanced noise/jitter ﬁltering, quality

monitoring, and fault detection capabilities.

The iC-TW8 requires only two external components

for operation, a serial EEPROM for storage of con-

ﬁguration and calibration data, and a clock oscillator

or crystal. An internal RC oscillator is provided for

cost-sensitive applications. Split analog and digital

power supply inputs allow optimal ﬁltering for noisy

industrial environments. An integrated power-on re-

set circuit can be overridden by an external hardware

reset signal if necessary.

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