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DS90UB933-Q1: External oscillator start-up time requirement

Andy Snawerdt
Intellectual 2650 points

Part Number: DS90UB933-Q1

Hello Team,

Hope all is well. Quick question regarding the external oscillator mode of operation for this device. Is there a start-up time requirement for the external oscillator? From the datasheet specifications this doesn't seem to be the case, but thought i'd do my due diligence to verify that the only requirements are with regards to jitter and stability as the datasheet implies:

Thanks for the help!

-Andy

  • 0
    TI__Mastermind 18755 points

    Hi Andy,

    Can you clarify what you mean by start up time requirement?  If the external oscillator supplied to the serializer meets the requirements laid out in the datasheet it should work as expected.  There is information regarding the requirements of the external oscillator in section 7.4.1 of the 933 datasheet.  

    Regards,

    Nick

  • 0 in reply to Nicholas Darash
    TI__Intellectual 2650 points

    Hello Nick,

    Thanks for getting back to me. Here's an app note explaining oscillator start-up: http://www.ti.com/lit/pdf/SNAA020

    I don't think it's something we really are concerned with in this instance given our power-up sequence is as follows:

    Given that PDB dictates whether the internal PLL is active or not, and we specify a max of 16ms for this, unless the oscillator start-up is ridiculously slow, I don't see any issues. Typically the external oscillator in these applications is powered off of VDD_n, so it's starting up as the device is being powered on as well.

    If you could check with some other apps folks and validate this for me, that'd be fantastic!

    Thanks,

    Andy

  • 0 in reply to Andy Snawerdt
    TI__Mastermind 18755 points

    Hi Andy,

    Sorry for the confusion on this. You are correct, the oscillator is typically powered from VDD_n so as long as the signal is present when the PLL is active there should not be any issues. Are you experiencing a problem that you believe is related to this power sequence?

    Regards,

    Nick

  • 0 in reply to Nicholas Darash
    TI__Intellectual 2650 points

    Hi Nick,

    No worries, thank you for the verification! No, we aren't experiencing any issues. Customer was just looking to swap the external oscillator in their design and wanted to ensure the start-up of the new oscillator wouldn't be an problem.

    Regards,

    Andy