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CCS/SFRA: Surge on low frequency

Michael Koval27
Intellectual 990 points
Part Number: SFRA

Tool/software: Code Composer Studio

Hello! Could any expert give to me idea, why my device shows  so great surge on low frequency 0-2 Hz ?

It is usual full bridge buck booster .

here is full range in Compensation Designer:

  • 0
    TI__Mastermind 43730 points

    Michael,

    Your injection amplitude is fairly high for the 70-80dB gain you have at low frequency,

    you will need to use a lower injection amplitude.. if you cannot do that you will need to accept those values as noise

  • 0 in reply to Manish Bhardwaj
    Intellectual 990 points

    Manish, yes, we tried any injection, and what is interesting, this surge is seen in any our expriments with this scheme. And as you see, even we tried with low resolution ( 1-10 Hz). These surges never disappear. I ask only suggestions what is the case of them, may be you have experience, if not ones, then all OK, they do not bother us much.

  • 0 in reply to Michael Koval27
    TI__Mastermind 43730 points

    Michael,

    From a SW side the SFRA logic is solid, but possible causes can be

    1. Noise (note the lab environment also has noise from nearby equippment etc)
    2. Injection value
    3. Fixed point code, (we may be hitting some numerical limits because the gain is too high), if you have the choice you can select and see if the floating point code resolved these issues.
    4. Steps , we do have some limits the injection we generate and we could be running in some corner cases with such low frequency. (we will have some updated to SFRA lib in the future , not planned yet)

    I believe my best advice based on experience will be to ignore these spikes ,

    I am not sure if you have tried an external frequency response analyzer, but it will also have similar behavior with noise creeping in when doing FRA at such low frequency as the time period is large for noise to couple through..