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TPS40422: Compensation Suggestion

Allan Fan
Expert 6910 points
Part Number: TPS40422

Tool/software:

Hi expert,

Customer used TPS40422 for 12Vin to 0.88Vo/40A and use the calculation tool for compensation but find the phase/gain margin is not good. 

Would you please advise how to adjust the stability?

TPS40KType III Loop Stability kVenable_sluc263c-5420M setting.xls

Thanks,

Allan

  • 0
    TI__Expert 3650 points

    Hi Allan,

    I noticed that you had 20 A, instead of 40A for IOUT Max. I changed this in the spreadsheet and got some better margins. 

    Regards,

    Maha

  • 0 in reply to Maha Noor
    TI__Expert 6910 points

    Hi Noor,

    I'd like to clarify/update some parameters in the spread sheet. 

    Here is the schematic. 0.88V 40A 2phase TPS40422.pdf

    Customer used it as dual phase configuration. 

    Q1: for the PSU parameters, should we fill in per phase parameters or as a total dual phase perspective? Cause if we only increase the IOUT_max to 40A, the stability is still not good. 

    The example below is single phase perspective. Should we adjust current to total maximum 40A, Lout/2 = 0.18uH, 2x ECAP &6x ceramic cap Qty *2?  

    Now there are two ECAPs per phase, so total are 4 ECAPs for example.   

    Would you please help modify the spread sheet with minimum changes for a good stability to us as a good reference? So we can be more clear what changes we need to do.

    Thanks,

    Allan

  • 0 in reply to Allan Fan
    TI__Expert 3650 points

    Hi Allan,

    1. Fill in per phase parameters.

    2. The first issue is that the crossover frequency is set to 500 kHz. Also, the schematic shows 16V 47uF ceramic capacitors, which have an ESR of 3mOhms, not 0.3mOhms. Also, the ESR for the polymer capacitors seem low. Please make sure that is correct. After changing the crossover frequency to 60kHz, updating the capacitor ESR and the polymer capacitor quantity, I also updated the zeros and poles as well:

    - First zero: 7.5kHz (LC resonance)

    - Second zero: 10 kHz

    - First pole: 60kHz (estimate of ESR zero of the 470uF capacitor)

    - Second pole: 250 kHz (1/2 switching frequency)

    This shows about 50kHz of bandwidth and 57 degrees of phase margin. 

    Regards,

    Maha