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TPS53355: question about calculation tool

user021864
Intellectual 2145 points
Part Number: TPS53355

Hi, 

My customer is having some questions for the calculation tool: 

1. Can we change the load step setting if we want to have other load step for calculation? 

2. what is the unit of the output ripple in blow capture? Is it peak or peak to peak value? 

3. Can you tell us how to get the equation of the Cout transient in the tool? 

Great thanks for your help on this case! 

  • 0
    TI__Guru**** 191445 points
    Hi user,

    My design tool is significantly different. It does not calculate any of that. Where did you get the tool you are using? Can you forward it to me directly?
  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    Gary,

    That is different from the work sheet I have, but let me answer your questions. It will be a short version as the long version got erased.

    1. That cell is in output not an input. It is fixed 70% of Iout. If you want, you can unlock the sheet and change 0.7 to some other value.
    2. That is not really a ripple spec. It is the delta Vout allowed during the load step.
    3. I have seen a couple different equations for the capacitance needed to meet a load step. That one is different than what I have seen previously. I am reasonably sure it is a simplification of the rather complex equations shown in this app note:
    www.ti.com/.../slva874.pdf
    Also, in the spreadsheet there is a modifier to estimate dc bias on the capacitor. I will leave it to you to derive the equations if you feel the need.