Here is a slightly older revision of the Si5351 data sheet before some marketing person possibly demanded that the data sheet had too much technical gibberish and scary numbers in it, and that needed to be fixed.?
The output drivers are current limited with programmable levels of 2, 4, 6, and 8 MA.
Also, the spec sheet claims the DC output impedance is 85 ohms when the 8MA drive is selected. Maybe they think that is close enough to the 50 ohm transmission line they use in the examples that it provides a source side impedance match. In moving data across transmission lines, ribbon cable, twisted pairs and such (usually more like 100+ ohms) you only need to match the source with a series "termination" resistor or the load with a parallel terminating resistor.?
Tom, wb6b
