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DS90C187 / Minimum transition time of TCIT and TXIT

S.Satoshi
Guru 21675 points
Other Parts Discussed in Thread: DS90C187

Hi Everyone,

Let me ask about minimum transition time of TCIT and TXIT. Generally I understand that maximum time should be defined for such transition time. But now I'd like to know the reason you define the minimum transition time. And how about your concerns when the transition time will be less than these minimum time.

Your comment will be appreciated.

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Mastermind 29655 points
    Hi Sonoki-san,

    A minimum time is specified in order to protect the LVCMOS I/O pins. The LVCMOS pins are sensitive to overshoot or undershoot voltage beyond the minimum or maximum specification allowed for LVCMOS pins. If the edge rate is too fast, the LVCMOS pin may not be able to respond to the fast edge rate, resulting in reflections. These reflections can ultimately result in the ESD diodes turning on at the LVCMOS pins.

    To prevent this type of potential damage, we have provided the minimum edge rate in the datasheet.

    Thanks,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Guru 21675 points
    Hi Michael,

    Let me ask one more question.

    I understand that the minimum transition time is specified to prevent damage due to over/undershoot. Then can you accept the transition time less than minimum spec if there is no over/undershoot on customer board? My customer is evaluating DS90C187 on their test board and confirmed there is no over/undershoot that is over abs max.

    Your comment will be appreciated.

    Best Regards,
    Sonoki
  • 0 in reply to S.Satoshi
    TI__Mastermind 29655 points
    Hi Sonoki-san,

    I do not think there will be an application issue with the minimum transition time if your customer ensures no overshoot or undershoot.

    However, please note that since we have not characterized the IC beyond the minimum and maximum transition time, we are unable to guarantee performance reliability from our ATE production. Therefore, I recommend implementing a way to slow down the incoming clock edges to the DS90C187 so that your customer can remain within our datasheet specifications.

    Thanks,

    Michael