SNAU279A July 2022 – September 2022
The LMK5B33414 has an XO input (XO pin) to accept a reference clock for the Fractional-N APLLs. The XO input determines the output frequency accuracy and stability in free-run or holdover modes. For synchronization applications like SyncE or IEEE 1588, the XO input would typically be driven by a low-frequency TCXO or OCXO that conforms to the frequency accuracy and holdover stability requirements of the application. For proper DPLL operation, the XO frequency must have a non-integer frequency relationship with the VCO output frequency of any APLL that uses the XO input as its reference. The non-integer relationship should be greater than 0.05 away from an integer boundary (meaning > 0.05 and < 0.95). When configuring the LMK5B33414 as a clock generator (DPLL not used), then the XO frequency can have an integer relationship with the APLL output frequency.
The XO input of the LMK5B33414 has programmable on-chip input termination and AC-coupled input biasing options to support any clock interface type.