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6.3.2.3
Layout Recommendations
6.3.3
RIOCLK/RIOCLK Solutions
Clocking
Figure 2. PLL1, PLL2 Multiple Device Clock Solution
Another solution would be to use very low jitter PLL clock generators/buffers. TI’s CDCE706 and
CDCE906 have been tested with at 25MHz and 50MHz and shown to meet the required jitter
specifications.
Placement, Terminations
•
The oscillator should be placed close to the destination.
•
Series termination should be placed close to clock source.
•
The value of the series termination resistor should be optimized to reduce over-shoot and under-shoot
while not violating the Trise/Tfall input specification. TI suggests the customer use IBIS simulations to
determine the correct value of the termination resistor.
Trace Routing
•
A GND plane should be placed below the oscillator.
•
Digital signals should not be routed near or under the clock sources.
•
Maintain at least 25 mil spacing to other traces.
The SerialRapidIO reference clock requires special considerations because it is differential, must be low
jitter, and requires termination. Either an LVDS or LVPECL clock source can be used but they require
different terminations. The input buffer sets its own common mode voltage so AC coupling is necessary. It
also includes a 100ohm differential termination resistor, eliminating the need for an external 100ohm
termination when using an LVDS driver. For generation information on AC termination schemes, refer to
AC Coupling Between Differential LVPECL, LVDS, HSTL and CML (
scaa059
). For information on DC
coupling refer to DC-Coupling Between Differential LVPECL, LVDS, HSTL, and CML (
scaa062
) .
SPRAAC7B – April 2006
TMS320TCI6482 Design Guide and Migration from TMS320TCI100
11
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