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TPS40210EVM: Bode plot frequency limit

Part Number: TPS40210EVM

I noticed that the EVM user's guide Figure 9 has the bode frequency up to 1Mhz.  The design switching frequency is 600 kHz.  I have heard from a number of power designers that the bode plot is only valid up to half the switching frequency.  So in this case it would be 300 kHz.  What is the explanation behind this 50% of fsw rule?  Here are a few articles they briefly mention about this but it's not very clear or layman:

https://www.infineon.com/dgdl/an-1162.pdf?fileId=5546d462533600a40153559a8e17111a

https://www.researchgate.net/publication/224083638_Measurement_of_the_Loop_Gain_Frequency_Response_of_Digitally_Controlled_Power_Converters

-kelvin

  • Kelvin,

    Thanks for reaching out with your questions.

    The measured bode plot is accurate up to the switching frequency. Typically, the commonly used mathematical models are only accurate up to 1/2 the switching frequency. In order to keep the models intuitive the most models don't take into account some second order affects of the control loop. In summary the measures loop is relevant up to the switching frequency but most models are only accurate up to 1/2 the switching frequency.

    Thanks,

    Garrett