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WEBENCH® Tools/TPS56C215EVM-762: WEBENCH efficiency calculation formula

Roy Chou
Prodigy 120 points
Part Number: TPS56C215EVM-762
Other Parts Discussed in Thread: TPS56C215,

Tool/software: WEBENCH® Design Tools

Hi all

I used the TPS56C215 recently and I did the efficiency simulation in WEBENCH designer and I changed all the part number the same as user guid TPS56C215EVM-762.

And the simulation results have around 3%~4% difference when output current is 1A~2A,and have 2%~3% difference when output current is 2A~3A and have 1%~2% difference when output current is 3A~4A. I would like to know why the difference become smaller wher output current larger. (I also test the real board-TPS56C215EVM-762, the results is similar to user guide so I think the problems occur in simulation)

So I would like to know how efficiency calulated by WEBENCH.(efficiency formula) and could you list the loss list which you have considered.(Like switching loss, conduction loss, PCB layout loss, DCR loss, iron loss, copper loss etc) Thanks.

Regards,

Roy 

  • 0
    TI__Expert 5745 points

    Normally the loss list WEBENCH consider show as below. For more detail, I'll reply you later after WEBENCH team give me the accurate results . Thank you!

  • 0 in reply to Vental Mao
    TI__Intellectual 1045 points
    Hi Roy,


    1. Usually Webench efficiency is within 3%(Maximum) mismatch compared to board efficiency.

    2. Below equation is used in Webench for efficiency calculation, with this equation efficiency displayed in “Opvals” table will match.

    Efficiency = Pout/(Pout+Pd) = (Vout*Iout)/((Vout*Iout)+Pd)
    Where Pd = Total power loss.

    Best Regards,
    Mahantesh
  • 0 in reply to Mahantesh Chanagoudar
    TI__Expert 5745 points

    Mahantesh：

    thank you for your help!

  • 0 in reply to Mahantesh Chanagoudar
    Prodigy 120 points
    Hi Mahantesh

    I also have a question about it. I clicked the Op vals button and it showed my Operating values like Vental showed. One confused point in it is I exported the Operating Values, the frquency showed in it is 800kHz ,but my mode pin is selected to 1.2MHz and the time domain was also 1.2MHz.
    So the efficiency chart's frquency was based on which frquency? Thanks.

    Regards,
    Roy
  • 0 in reply to Roy Chou
    TI__Intellectual 1045 points

    Hi Roy,

    Currently on Webench we have enabled only two frequencies .i.e 400kHz and 800kHz as highlighted in below image. Efficiency will be calculated for frequency displayed in Opvals. 

    Since 1.2MHz is not enabled on Webench it will show only 400kHz or 800kHz in Opvals table.

    Best Regards,

    Mahantesh

  • 0 in reply to Mahantesh Chanagoudar
    Prodigy 120 points

    Hi Mahantesh

    Thank you for your help. Also have two things would like to ask you.

    1. Could I simulate the other parameters(like Iin Average,root mean square) in Performance summary?

    2. When I saw the OP val, it showed the one of the Power dissipation is from IC loss.

    Could you tell me how the IC loss calculate or include? like switch loss, conduction loss, driver loss etc.

    Or you could provide me the formula. 

    Thanks.

    Roy 

  • 0 in reply to Roy Chou
    TI__Intellectual 1045 points

    Hi Roy,

    1. Currently we are not displaying parameters like Iin Avg, root mean square values in performance summary.

         However you can find Iin avg, Cin Irms and Cout Irms in Opvals as shown in below image.

       

     2.  IC Pd includes/calculated using below equation.

       a. If High side FET is on, below is the IC_Pd loss calculation equation.  

    IC_Pd = {Pdiss_IC_quiescent +  Pdiss_FetHS_Conduction+Pdiss_FetHS_GateCharge                                  +Pdiss_FetHS_Rise+ Pdiss_FetHS_Fall+Pdiss_FetHS_Coss+Pdiss_FetLS_ReverseRecovery }

    b. If Low side FET is on, below is the IC_Pd loss calculation equation.  

    IC_Pd = {Pdiss_IC_quiescent + Pdiss_FetLS_Conduction+Pdiss_FetLS_GateCharge +Pdiss_FetLS_Coss +Pdiss_FetLS_Diode +Pdiss_FetLS_Fall}

    Where, Pdiss= Power dessipation

                  FetLS= FET low side,FETHS=FET High Side.

    Best Regards,

    Mahantesh

  • 0 in reply to Mahantesh Chanagoudar
    Prodigy 120 points

    Hi Mahantesh

    I still have some question about  below formulas. Because there are having 2.5% difference between simulation and experiment.(experiment is good) May I ask you about the ic loss parameters(Rdson Ciss Coss Qg) about TPS56C215(12V→1.2V) output current 1.2A/2.4A/3.6A/4.8A or you can give me more detailed calculation. Thanks.

    IC Pd includes/calculated using below equation.

       a. If High side FET is on, below is the IC_Pd loss calculation equation.  

    IC_Pd = {Pdiss_IC_quiescent +  Pdiss_FetHS_Conduction+Pdiss_FetHS_GateCharge                                  +Pdiss_FetHS_Rise+ Pdiss_FetHS_Fall+Pdiss_FetHS_Coss+Pdiss_FetLS_ReverseRecovery }

    b. If Low side FET is on, below is the IC_Pd loss calculation equation.  

    IC_Pd = {Pdiss_IC_quiescent + Pdiss_FetLS_Conduction+Pdiss_FetLS_GateCharge +Pdiss_FetLS_Coss +Pdiss_FetLS_Diode +Pdiss_FetLS_Fall}

    Regards,

    Roy

  • 0 in reply to Roy Chou
    TI__Intellectual 1045 points

    Hi Roy,

    Internal MOS parameters and detailed loss equations are TI proprietary these can not be shared

    Best Regards,

    Mahantesh