iC-TW8 16-BIT SIN/COS INTERPOLATOR
Pin Configuration Mode
Jan 9, 2013 Page PC6/15
Power-on-Reset
The iC-TW8 contains a built-in power-on-reset
(POR) circuit that controls the safe start-up of the
device. The internal POR can be configured for
two thresholds, 2.7V for use with 3.3V supplies or
4V, which is recommended when operating the
iC-TW8 at 5V. Connect xRST (pin 2) DVDD or
leave it unconnected (xRST has an internal 40kΩ
pullup resistor to DVDD) to select a power-on-
reset threshold of 2.7V. Connect xRST to ground
through a 68kΩ resistor to select a threshold of 4V.
An external reset source (such as an RC circuit) can
also be connected to xRST (pin 2) to directly control
the POR behavior.
Connect xRST to DVSS via 68kΩ
resistor for 4V POR threshold.
DVDD
xRST
xRST
68kΩ
Connect xRST to DVDD (or leave
floating) for 2.7V POR threshold.
iC-TW8
iC-TW8
DVSS
Figure 8: Setting the Power-On-Reset Threshold
Providing a Clock
The iC-TW8 supports three clocking modes as
indicated in Figure 9. While the iC-TW8 provides
an internal oscillator, it cannot be tuned in pin
configuration mode. 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 varia-
tions, 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 Fig-
ure 9. Depending on the crystal characteristics, two
capacitors to ground might be necessary for stable
oscillation. To use an oscillator or ceramic resona-
tor, connect XIN (pin 35) to ground and the oscilla-
tor 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. Mini-
mum frequency is 6 MHz regardless of supply volt-
age.
To use the internal oscillator, connect both XIN (pin
35) and XOUT (pin 34) to ground as shown in Fig-
ure 9. The iC-TW8’s internal oscillator has a nomi-
nal frequency of 20 MHz with 5V supplies and 16
MHz with 3.3V supplies. However, manufacturing
tolerances and changes in temperature can cause
large variations in the frequency of the internal os-
cillator.
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