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CDCM6208 smart mux

Frank Xiao
Genius 12055 points
Other Parts Discussed in Thread: CDCM6208

Hi Team,

The CDCM6208 has Smart Mux function. From the description, the Primary and Second input can auto change. So we want to know, for the 'smart lock', it will determine the MUX depend on the whether the input clock is exist or not. Or depend on whether the output PLL unlock or not?

When one channel clock disappear, when the Smart Mux change one channel to another. Does it will influence the output clock?

Thank you.

BR

Frank            

       

  • 0
    TI__Expert 5325 points

    Hello Frank,
    the "smart mux" checks if the primary reference input has a continuously toggling clock. When it stops toggling, it will switch to the secondary reference clock. This will keep the amount of missing clock cycles to a minimum. This can lead to a PLL unlock. Therefore it is important to design the PFD update frequency and the closed loop bandwidth accordingly. The feedback loop should update so slowly, so that it does not see the switch between the two references. Ideally there is only an analog phase pull, but no frequency unlock.

    The LOS status signal and bit will show which of the input reference are deemed "active".


    Best regards,
    Patrick

  • 0 in reply to Patrick Kammermayer
    TI__Genius 12055 points
    Hi Patrick,

    Thank you for your help. Could you please explain detailly about how to design the PFD update frequency and the closed loop bandwidth? I need to explain it to the customer and give the suggestions how to set it. Thank you.

    BR
    Frank
  • 0 in reply to Frank Xiao
    TI__Expert 5325 points

    Hello Frank,

    you can find a general description how to optimize PLL circuits here: http://www.ti.com/tool/pll_book

    For CDCM6208 you can use Webench or the EVM GUI. Both include phase noise simulation.

    Webench will recommend a setting for best phase noise performance.

    For help to design the clean switch-over, the customer needs to provide some specs what timing they can tolerate in the system.

    Best regards,

    Patrick