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TMS320F280049: Question about Crystal Oscillator start-up time

Huihuang Chen
Expert 4060 points

Part Number: TMS320F280049

Hi Champ,

in the datasheet  the TYP start-up time is 2mS ,like following figure ,

while customer used following parameter, please advise how to calculate the start-up time.

Another question is: the TYP start up time in datasheet is 2mS , why in TRM 3.7.7 chapter mentioned 1ms is the TYP wait time?

  • 0
    TI__Mastermind 28275 points

    Hi Huihaung,

    It is not really feasible to calculate the XTAL start-up time. It is a parameter that you would have to characterize yourself as it heavily depends on the crystal, load capacitors, ESR etc. These are parameters outside TI's control as we don't make the crystals. This is the reason why the numbers in the datasheet are typicals.

    To measure the start-up time, you can just bring out the XTAL signal on the XCLKOUT pin. Ater that, you turn the XTAL on and measure the time delta between when the XTAL is turned on to when the duty cycle on XCLKOUT is within 40-60%. If your customer is not able to perform this measurement themselves, they should have the crystal vendor do it.

  • 0 in reply to Frank Ankapong
    TI__Expert 4060 points

    Hi Frank,

    I don't think your reply solved my issue.

    We know the start-up time depends on the crystal, load capacitors, ESR etc.

    But please provide the calculate method based on the crystal, load capacitors, ESR etc.

    Or did you means the TYP 2mS is just based on the real testing result and TI don't have the principle to calculate it?

    Also i didn't see your reply on below question:

    Another question is: the TYP start up time in datasheet is 2mS , why in TRM 3.7.7 chapter mentioned 1ms is the TYP wait time?

  • +1 in reply to Huihuang Chen
    TI__Mastermind 28275 points

    Huihaung,

    We don't have calculations or models for this but I'm sure you can find something online if that is the route you want to take. The numbers provided in the datasheet were from measurements we did. I will file a ticket to change the TRM to 2ms.

    Nevertheless as I mentioned in the previous reply, please don't get hang up on the typical 1ms, 2ms etc that we specify in the documentation as it is only really valid for the specific crystals that we used for the tests. This is the reason why everywhere you see the start-up time mentioned in the documentation, there are disclaimers. It should only be used as a very loose guideline.

  • 0 in reply to Frank Ankapong
    TI__Expert 4060 points

    Frank,

    Noted and Thanks!