I would like to use Si5351A-B-GT with 2.8V VDD and 1.8V VDDO.
Datasheet implies the core supply voltage (VDD) needs to be either 2.5V or 3.3V. Any reason this part shouldn't be used at 2.8V?
2.8V is fine. You can use VDD = 2.8V and the part cannot detect the actual input voltage level as it regulates this to another internal voltage internally.
We state 2.5V and 3.3V standards because they happen to be the ones that are used in most systems.
Thank you for your response. Sounds good.