AD8436 RMS-core occur overshoot

Hi

I have question about AD8436.

 

When 5Vin start-up condition at ADI EVB/LTspice, RMS-CORE occur overshoot.

Is it normal operation? Or what is this reason?

 

CH1:TRMSIN(AC123mV+DC1.65V),CH2:Output-Buffer,CH3:RMS-CORE Output,CH4:+5V

 

Best Regards,

Yu

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    •  Analog Employees 
    on Oct 21, 2020 12:51 PM in reply to mochii

    Hi Yu,

    If you look at the current through CAVG, you will see a spike in response to a sharp transition.  The sudden change in voltage would appear as a signal (i.e. much AC content in the transition).  After power up and any DC step for input signal, there should not be any overshoots unless there are further sudden changes in DC level.  Would other sudden transitions in DC levels be expected during normal operation?  Thanks.

    Cheers,

    George

  • Hi George,

    Our problem is OBUFOUT’s overshoot when 5V on.

    When 5V on, OBUFOUT occur overshoot because CAVG capacitor is charged.

    Please let me know how to prevent this overshoot.

     

    Our system shut down when it sees abnormal value at OBUFOUT.

    Therefore I want to avoid CAVG overshoot when 5V on.

    Best Regards,

     

    Yu