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TPS40210: TPS40210DGQR phase margin

Diego Rossini
Prodigy 80 points
Part Number: TPS40210

Hi all,

I have done a step-up with a TPS40210DGQR: Vin is 24V nom, and Vout is 52V, 0,75A nom (attached image).


I must to change dinamically the output voltage, from about 44V to 63V. To do this I would like to change R1 in order to increase or decrease the vout.


My issue regards the phase margin.. If I change the R1 value, It could be that I must to change the compensation network too, in order to keep the correct phase margin.. But I can't change dinamically the compensation network..


I tried to change the value of R1 into the webench Power Designer, then I done some simulations and trace the bode diagrams. My target is: any changing of R1 cause a permissible phase margin change. In the proofs that I have done the phase margin is always the same.. How it's possible?


The principal value of R1 are:

  • 750ohm for 44V, about 100W;
  • 634ohm for 52V about 100W;
  • 520ohm for 63V about 100W.

With these value, I have some dangerous configuration?
How can I verify these situations?

Thanks in advance, best regards,
Diego.

  • 0
    TI__Mastermind 21720 points
    Hi Diego,

    Thanks for reaching out with your questions.

    In regards to the TPS40210 changing the lower feedback resistor will not change the compensation network transfer function as the FB pin is an AC ground. The transfer function that is modified with a varied output voltage is the plant function. To compensate the loop, the compensation components should be calculated for the worst case operating condition. The worst case operating condition occurs when the input voltage it the minimum value, the output is at the maximum value and maximum load current.

    Please let me know if you have any questions.

    Thanks,

    Garrett