Adjusting OCXO frequency via VFC pin
Reference pin accepts, not provides volatge,


Based on the datasheet, this appears to be incorrect:



If the datasheet describes the pin as an output, it usually means it is an output from the chip, not an input to the chip. And  by "usually" I mean in every instance I've ever heard of.

The intent of this pin is probably to provide a reference for a DAC to be used to drive the Uin pin. Or, for manual control you could connect a potentiometer between Uref and ground, and connect the wiper to Uin.

Sometimes it's possible to override a reference output pin with an external voltage, but I don't see anything in this (rather terse) datasheet to indicate that is possible with this chip.