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TMS320F280039C-Q1: maximum acceptable start-up time requirement

Fan_Zhang
Expert 4530 points

Part Number: TMS320F280039C-Q1

Hi, experts,

I am asking this question on behalf of my customer.

In datasheet, only TYP value of start-up time is listed in the table.

While customer uses following parameters, and their calculated start-up time is different with the TYP value in datasheet.

They want to know the maximum acceptable start-up time requirement for F280039C, and if below parameters work with F280039C.

Thanks. 

  • 0
    TI__Mastermind 25380 points

    Hi Fan,

    The expert is currently out of office until later next week. Please expect a delayed response.

    Best Regards,

    Delaney

  • 0 in reply to Delaney Woodward
    TI__Guru* 84940 points

    Fan,

    The important outcome of the above circuit is that the external crystal is up and running by the time the C2000 MCU attempts to switch to that clock source.  As the DS mentions these are just typical values, and different X-tal's can take more or less time.

    I don't see anything incorrect in the schematic, since there is no load resistor(Rd), a longer start up time would imply the ESR of the crystal may be higher than what we used to create this section of the DS.

    With that said, as long as the start up time is repeatable, customer can accommodate that in his initialization code when setting up/turning on the X-tal in his code exaction before switching from the internal oscillator to this external device.  As long as the crystal is stable before we use it for the main CPU clock it should be OK.

    Best,

    Matthew