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TPS40304: Loop compensation Web Bench vs spreadsheet?

Eric Hanisch
Prodigy 10 points
Part Number: TPS40304

Tool/software:

Trying to do a TPS4030 1.8V design and the online tool and the compensation spreadsheet seem to disagree with my values.  I am leaning towards believing the spreadsheet more than the online tool.  The online tool of course I cant put in my exact FETs and caps of course either still. 

 Trying to maybe provision for an EMI filter as well since we have to meet CISPR 25 Class 5 on most devices now.

 Basically, the online tool is saying phase margin is 30.41 with the below

 I am planning on using the spreadsheet tool values and everything seems fine:

 

  • 0
    TI__Guru 55230 points

     

    If you aren't able to find the right inductor and output capacitors, the excel spreadsheet is a good alternative, as long as you apply the derating factors, which is appears you have.

    The phase drop just above 10kHz looks a little low in the excel spreadsheet.  This is because the ESR damping on the L-C resonance is very low and the default ratio for the 2 Zeros with one zero at 2x the L-C frequency and one at the L-C frequency is a little too high, lowering the higher one to the L-C frequency will provide more phase boost at L-C resonance.

    If you would like to boost the phase there:

    1) Type in the existing Pole and Zero frequencies into the manually entered pole and zero frequencies lines next to them

    2) Reduce the manually entered  Fz_1 (Frequency of Zero 1) from 14469Hz to 8000Hz (the L-C resonance frequency

    3) Change the "manually enter Rs & Cs" selection to "No"

    4) Change the "manually enter Ps and Zs" selection to "Yes"

    The calculator will update the resistor and capacitor values for the manually entered Pole and Zeros and boost the phase at resonance.

    If you are thinking about adding a secondary filter after the main filter, I would recommend connecting the VOUT before the filter and the VOUT after the filter together with a resistor to the VOUT after the filter and an R-C in parallel to Vout before the filter.  That way you can regulate the DC voltage after the drop across the secondary filter while maintaining stability based on VOUT before the secondary filter by adjusting the R and C ratios.