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ADS1258 crystal

Bruce Shutts
Prodigy 40 points
Other Parts Discussed in Thread: ADS1258

Hi.  I am having trouble with the ADS1258 crystal starting at cold temperatures.  Our spec is -40 deg.  The crystal is ECS-.327-12.5-13FLX-C.  The ESR is 50K which is more than the converter spec recommends.  Once oscillating it will usually continue at cold temps but if stopped it will not start.  What crystal would you recommend for this application? 

Thank you,

Bruce

  • 0
    TI__Mastermind 44680 points

    Hi Bruce,

    Table 4 in the ADS1258 datasheet gives recommendations for crystals; each was tested with the ADS1258 across temperature. The crystal you mentioned is similar to a recommended one, but in a different package.

    It could be the layout and/or the loading capacitance that is giving you problems. What value capacitors do you use? Also, is the crystal placed right next to the the ADS1258 or do you have some significant trace lengths between the ADS1258 and the crystal?

    For clarification, the ESR spec is typically one that you do not want to exceed. Higher ESR crystals require more drive strength and are more likely to have start-up issues.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    Prodigy 40 points
    Chris,

    Thank you for your reply. The capacitors were originally 18pF. Raising them to 22pF helped some at cold temperatures. Below 18pF the oscillator would usually not start.

    The crystal is mounted very close to the oscillator pins. Total trace length is approximately 120 mils. The capacitors are also mounted close to the crystal.

    Bruce