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LMK00101: two questions concerning the LMK00101

Nir Flysher
Expert 3367 points
Part Number: LMK00101

Dear Team,

My customer has two questions regarding the LMK00101 I hoped you could help us with :

1. Is it possible to drive the input clock CLKIN0 before the powering of the device? Can it cause damage ?

2. What is the recommended termination in CLKIN0 if my input clock is defined as LVPECL AC coupled?

Best regards,

Nir.

  • 0
    TI__Mastermind 24205 points

    Hi Nir,

    1. Is it possible to drive the input clock CLKIN0 before the powering of the device? Can it cause damage ?

    In general, it is not considered a good idea to drive the input clock CLKin0 before applying core power to LMK00101 device as it technically violates the ABS MAX RATINGS stated in the datasheet. We do not recommend doing this. However, if the reference input is a differential signal, there is typically low risk of having a sufficiently high current path from the driver through the input ESD structure on LMK00101 that would be sufficient to turn on additional logic on the board through the Vcc pin or result in permanent damage.

    2. What is the recommended termination in CLKIN0 if my input clock is defined as LVPECL AC coupled?

    LVPECL Driver -> Emitter resistor to ground -> AC coupling capacitor -> 100 ohms resistor across the diff pair -> LMK00101 input

    Regards

    Arvind Sridhar

  • 0 in reply to Arvind Sridhar
    Prodigy 215 points

    Hi Arvind.

    Thank you for your response.

    I understand from your answer that I don't have to put 133 Ohm Pull-Down and 82 Ohm Pull-Up on each line of the diff clock as usual in LVPECL. Is that correct?

    Best regards,

    David

     

  • 0 in reply to David Siksik
    TI__Mastermind 24205 points

    That's correct David. You don't have to have a thevenin termination if you are AC coupling the signal from a LVPECL driver to the LMK00101 CLKinx/x* input.

    Regards

    Arvind Sridhar