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Original question:

LMR38010-Q1: LMR38010-Q1: no feedback network compensation required?

LMR38010-Q1: LMR38010FS-Q1: Poles and zeroes of Bode Diagram

Alex L
Prodigy 60 points
Part Number: LMR38010-Q1
Other Parts Discussed in Thread: LMR38020

Hi ,

I found out using Webench that the LMR38010FS-Q1 is easily put into instability (Phase margin < 45°), e.g. for too small an output capacitance.

What kind of response function does the LMR38010FS-Q1 have?
What are the poles/zeroes as functions of inductance, input/output capacitance, feed-forward capacitance, Vin\Vout, Iout ?

How can I be sure that LMR38010FS-Q1 doesn't become unstable in both the complete Vin range and the complete Iout range ?

Is there a region where phase margin is minimum? I found out empirically that this seems to be the case for lowest Vin and lowest Iout. Is that true? How do you justify this assumption?

It seems neither Pspice for TI nor TINA do have the LMR38010FS-Q1 model. How can I simulate the DC\DC converter?

Thank you very much in advance

Regards

  • 0
    TI__Genius 13735 points

    hi, Alex,
    Thank you for the posting. We have provide LMR38020 webench and spice model, you can refer to for simulation and calculation.

    Usually follow the DS calculation guide you will get a stabile application circuit cross all Vin and Iout range, if you use the LC value too large or too small conscious that will lead loop unstable which is not recommend.

    LMR38020/10 in PCM internal mode, you can look detail into DS about the peak current section.

    Elena

  • 0 in reply to Elena Gao
    TI__Genius 13735 points

    hi,

    Since I didn't see update here, please reopen this ticket or start a new one if you still have question .I will make it close first, thank you for undersanding.

    Elena