iC-TW8 16-BIT SIN/COS INTERPOLATOR
Serial Configuration Mode
Jan 9, 2013 Page SC11/36
Providing a Clock
The iC-TW8 supports three clocking modes as
indicated in Figure 9. The iC-TW8 provides an
internal oscillator that, while it can be tuned, is
not particularly stable over temperature. Thus, an
external crystal or other clock source is recommended
for all but the most cost-sensitive applications.
XOUT
XIN
XOUT
XOUT
XIN
XIN
iC-TW8
iC-TW8
iC-TW8
Crystal
Clock Inject
Internal Oscillator
Figure 9: Clocking
An external crystal or oscillator provides the most
stable clock signal over time and temperature var-
iations, resulting in the most consistent long-term
iC-TW8 performance. Connect an external crystal
to XIN (pin 35) and XOUT (pin 34) as shown in
Figure 9. Depending on the crystal characteristics,
two capacitors to ground might be necessary for
stable oscillation. To use an oscillator or ceramic
resonator, connect XIN (pin 35) to ground and the
oscillator output to XOUT (pin 34) as shown in
Figure 9. Maximum crystal frequency (fclock) is
32 MHz with 5V supplies and 24 MHz with 3.3V
supplies. Minimum frequency is 6 MHz regardless of
supply voltage.
To use the internal oscillator, connect both XIN (pin
35) and XOUT (pin 34) to ground as shown in Figure
9. The iC-TW8’s internal oscillator has a nominal fre-
quency of 20 MHz with 5V supplies and 16 MHz with
3.3V supplies and can be tuned (see page 33). Howev-
er, manufacturing tolerances and changes in tempera-
ture can cause large variations in the frequency of the
internal oscillator.
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