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TMS570LS1114 max. clock input frequency

Tobias Maerki
Intellectual 390 points
Other Parts Discussed in Thread: TMS570LS1114

Hello

The TMS570LS1114 datasheet states a maximum clock input frequency of 20 MHz. If I use a 20 MHz quarz oscillator with 100ppm tolerance over temperature is the device guaranteed to work?

Is there an absolute maximum input frequency you could state or at least a rough number where the limits are (i.e. 20.1 MHz / 20.5 MHz / 21.0 MHz)?

Best regards

Tobias

  • 0
    TI__Mastermind 20060 points

    Tobias,

    Every crystal has tolerance. Our part comprehends oscillator tolerances.

    If I understand your spec right, you could differ from 20MHz by as much as 100 Hz. That is equivalent to 20.0001 MHz .  When multiplied by 8 (to get to 160MHz) or 9 (to get to 180 MHz), the final frequency ends up as 180.0009 MHz. Our part will run over temperature with this much frequency variation.

    Best regards,

    Kevin Lavery

  • 0 in reply to Kevin Lavery
    Intellectual 390 points
    Hi Kevin
    Thank you for the reply.

    My tolerance calculation would be like this:
    Nominal clock frequency: 20 MHz
    Tolerance over operating temperature range +/- 100ppm: +/- 2 kHz
    Aging +/- 5ppm/year: +/- 2 kHz @ 20 years
    Total: 20 MHz +/- 4 kHz

    So my worst case frequency would be 20.004 MHz and thus slightly more than your 20.0001 MHz.
    Am I right to assume that the TMS design will still run with this tolerance?

    Best regards,
    Tobias Märki
  • 0 in reply to Tobias Maerki
    TI__Mastermind 20060 points

    Tobias,

    The crystal tolerance is comprehended in the specs.

    For concreteness, the 20.004MHz input would yield an output of 160.032MHz rather than 160MHz (or 180.036MHz rather than 180MHz). The part is designed to comprehend these tolerances.

    Best regards,

    Kevin Lavery

  • 0 in reply to Kevin Lavery
    Intellectual 390 points
    Thank you for the confirmation.
    Best regards,
    Tobias