[SI-LIST] Re: Termination of un-used clocks

Only occasionally have I seen a clock driver that wanted its unused
outputs terminated.

If a part has complementary outputs, and you use only the high-true
outputs, it is usually wise to terminate the low-true outputs with as
similar a load as possible to the load on the high-true outputs (same
trace length if end does not have parallel termination) to balance the
output currents.  This was often recommended with ECL.

Also we once used an ECL clock driver that worked best (lowest skew)
when similar loading was used on all groups of output pins.  If one
group had all its outputs used, and another had only one, there would be
a small(!) additional skew, which could be reduced by terminating unused
outputs (or at least terminating equal numbers of outputs on all sides
of the chip).

Sure there may theoretically be tiny reflections if an unused pin is
left open, but usually you can say, so what?

Andy



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