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LMK05318B: Details on Hitless Switching

Part Number: LMK05318B


Tool/software:

We’re tracking down an FPGA problem and had a question about the Clock Synth.  When the documentation says that it does a “hitless switchover”, that means that when the Primary (or secondary) reference is detected, the output will begin using that reference and the output clock will be seamlessly switched, right?  Like completely invisible to an outside observer, except the PPM and drift will begin to match the new reference, right?

Is the only way to detect this is if one of the LOR signals trigger correct?

  • Hi Jason,

    Yes, the switchover will be done in a way that the outputs are undisturbed and the receiver does not experience a significant "phase hit". This is done by the DPLL gradually and steadily shifting from the phase of the XO input to the phase of the reference input.

    What do you mean by "detect this"? Is this referring to a switchover event (holdover to reference and reference to reference)? The REFSWITCH_INTR register, R20 bit 3, can identify whenever a switch in reference or holdover has occurred.

    Regards,

    Jennifer