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Margin between |ZN(S)| and Damped |ZO(S)|

Liu Yang
Expert 8875 points

Hi Team,


About the Figure 17 at page 13, what is the difference (margin) between |ZN(S)| and Damped |ZO(S)| is it possible to consider that there is no problem in the operation of the DC / DC converter?
(Since a general value is acceptable, it would be helpful if you could give us an approximate number such as XXdBOhm)

Best Regards,
Tom Liu

  • 0
    TI__Genius 12735 points

    Hi Tom,

    I am looking into who on the team can help with this, you should receive a response within the next day.

    Best regards,

    Layne J

  • 0
    TI__Guru 56985 points

     

    The critical requirement for stability of the input is that the net impedance  1 / ( 1/Zo + 1/Zn ) is a positive value for all frequencies, but there should be enough margin such that variations in the damping or output impedance can't result in it becoming negative.  Generally, it is good to maintain 50% margin between Zo and Zn to prevent device or operating condition variations from creating an unstable condition.

  • 0 in reply to Peter James Miller
    TI__Expert 8875 points

    Hi Peter,

    Thank you for your reply.
    Please make sure that the following understanding is okay.

    (1) It is necessary that 1 / ( 1/Zo + 1/Zn ) is a positive value after considering error, during all frequency band. Here, Zn is Negative Impedance.

    (2) Regarding the margin, the value of Zo should be 1/2 or less of Zn after considering operating conditions and errors.
    We considered that the margin is larger than 6 dBΩ.
    If we have any errors in the understanding above, please let me know.

    Best Regards,
    Tom Liu

  • 0 in reply to Liu Yang
    TI__Guru 56985 points

     

    Yes, your understanding is correct