Premis SSCG filter values below 1%

Question: I need to set the FS781 filter values to give 0.3%, 0.5% and 0.7% spread bandwidth. They are running at 32MHz. What would the capacitor values be?

 

Answer:

In general the FS781 PLL design does not support spread percentages below 1%. The PLL loop becomes unstable as you choose filter values for the low spread selections. That is why we now offer the CY25811. The customer will have to switch to this part for low spread percentages.