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6.3.2.2
Fanout Solutions
Clocking
For CLKIN1 and CLKIN2, a low jitter CMOS oscillator would be sufficient. A series termination resistor
(nominally 22 ohms) at the source is suggested (refer to
Figure 1
). An example of an appropriate oscillator
is:
•
Vectron VCC1 series 3.3V CMOS oscillator
–
http://www.vectron.com/products/xo/vcc1.pdf
This oscillator has not been tested but is an example of an oscillator that meet the specification
requirements for CLKIN1 and CLKIN2.
Figure 1. CLKIN1, CLKIN2 Single Device Clock Solution
For systems with multiple TMS320TCI6482 devices it may be preferred to use one oscillator and a fanout
buffer instead of multiple oscillators. This would allow for fewer components as well as lower cost. The
fanout buffer increases the jitter at the clock input so care must be taken in selecting the combination of
oscillator and fanout buffer.
In most cases the same oscillators described in
Section 6.3.2.1
can be used for the fan out case. The
oscillator output specifications should be compared to the fanout buffer input specifications to make sure
they are compatible.
A low jitter fanout buffer is required which generally means a non-PLL based fanout buffer should be used.
Suggested solutions for fanout buffers are:
•
TI CDCV304 1:4 Clock buffer
–
http://focus.ti.com/lit/ds/symlink/cscv304.pdf
•
TI CDCVF2310 1:10 Clock buffer
–
http://focus.ti.com/lit/ds/symlink/cdcvf2310.pdf
•
CDCV304 jitter information:
http://focus.ti.com/lit/an/scaa052/scaa052.pdf
•
CDCVF2310 jitter information:
http://focus.ti.com/lit/an/scaa064/scaa064.pdf
Figure 2
shows a diagram of a solution that allows an oscillator and a fanout buffer to provide CLKIN1 or
CLKIN2 for up to 4 DSPs. Up to 10 DSPs could be supported with the CDCVF2310 which would be the
same circuit without the series resistors since the CDCVF2310 has built-in 22ohm resistors. The buffer
outputs should not be used to drive additional fanout buffers since the jitter will accumulate.
10
TMS320TCI6482 Design Guide and Migration from TMS320TCI100
SPRAAC7B – April 2006
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