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TPS548D22: Output impedance, What is Output inductance (Lout), Output Resistance(Ro)

Pankaj Ahirwar
Prodigy 30 points
Part Number: TPS548D22


What is simplified R, L model of this VRM ? 

Is output impedance Vs Frequency curve available ? 

Output inductance (Lout), Output Resistance(Ro) 

  • 0
    TI__Guru**** 191445 points

    We do not have that model.  It is mostly determined by the user selectable output filter components.

  • 0 in reply to JohnTucker
    Prodigy 30 points

    Hi John, 

    Is the output impedance ( R/L) value available or measured for TPS548D22 evaluation board. ?

    I can choose ESR of capacitors to match load_impedance.

    Though the output inductor is not a significant contributor to the output impedance, it is important

    to use an appropriate value. The relationship between the inductance the ripple current is:

     

    The VRM output impedance is more related to transconductance  up to switching bandwidth. (let’s say for a current mode converter)

    VRM requires a certain transconductance to provide a certain impedance. The first issue is that the control loop bandwidth cannot be infinite, so it must be restricted to a realistic bandwidth. In order to avoid the odd behaviors near the switching frequency, a practical limit for the frequency is 1/10th to 1/6th of the switching frequency. Above the bandwidth, the capacitor controls the impedance, so the capacitor ESR is equal to the target impedance.

    Is there an application note from TI which can explain on how to determine the output impedance based on user selected component values. 

    It'll be great if you can reach me at pankaj.ahirwar@huawei.com to further discuss about my application requirements.

    Best Regards

    Pankaj Ahirwar 

  • 0 in reply to JohnTucker
    Prodigy 30 points
    An application note on how to estimate output impedance from components will be handy to have.
  • 0 in reply to Pankaj Ahirwar
    TI__Guru**** 191445 points

    I doubt that we have any measured value as that is not a parameter we typically test or measure during EVM development.  I have measured the output impedance  in the past.  The plot seemed somewhat useless.  I can probably measure it on the TPS548D22 EVM, but I doubt I can get it before the holiday.