• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 166 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

SYNC-BUCK-FET-LOSS-CALC: Questions Regarding Power Loss Calculation in SYNC-BUCK-FET-LOSS-CALC Tool

Malek Hattab
Prodigy 65 points
Part Number: SYNC-BUCK-FET-LOSS-CALC

Tool/software:

Hello Support Team,

I am trying to estimate the losses in a buck converter. I used to perform the calculations manually and relied on my own Excel sheet, based on the references listed below, to optimize the circuit design of the converter and select the appropriate MOSFET. However, I recently found the SYNC-BUCK-FET-LOSS-CALC sheet on the TI website, which is an excellent tool as it provides a database for TI MOSFETs and suggests the most suitable one. Many thanks for providing this tool.

https://www.ti.com/lit/an/slvaeq9/slvaeq9.pdf?ts=1742177768019

https://www.ti.com/lit/an/slpa009a/slpa009a.pdf

The sheet is based on the second reference mentioned.

While comparing my results with the ones from the sheet, I noticed two concerns:

1. Power Loss Calculation for the Control MOSFET: I believe the power loss of the control MOSFET may be calculated twice. Please refer to the image below for clarification.

2. Qrr Losses for the Low Side MOSFET: The reference sheets use a specific formula for estimating the Qrr losses of the low side, but in the Excel sheet, the output of this formula is multiplied by Iout/20. Could you please clarify this difference? Also, what is the most accurate expression to estimate these losses?

The excel sheet is attached for you reference.

SYNC-BUCK-FET-LOSS-CALC_Rev2.01.xlsm

Thank you for your help.

Best regards,
Malek

  • +1
    TI__Mastermind 36770 points

    Hello Malek,

    Thanks for trying out the tool and providing your feedback. I think you're right about the error in adding up the HS FET losses. I believe the Qoss calculations are correct but I added the LS Qoss loss to the HS total instead of the LS. It should be an easy enough fix for me to implement. For QRR loss, I followed the example from an earlier loss calculator done by another TI engineer. QRR is tricky to measure and varies with current and di/dt. Without that factor the QRR loss becomes dominant and I'm not sure that's correct. I've done some correlation to the loss calculations and data in the app note and it's pretty close. I also use Rds(on) max from the datasheet at the closest value of VGS used in the design. That's typically 25% higher than the typical datasheet value. The intent of the tool is to help compare and select TI FET solutions and the accuracy is "good enough". I'll fix the calculation error and get a new version onto TI.com as soon as I can. Please let me know if you have any additional questions.

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    Prodigy 65 points

    Hello John,

    Thank you for your support.

    This is truly a great tool, and I’m really glad I found it.

    Regarding Qrr, I completely agree with you. The result from the equation without the factor seems quite high, and I've often wondered about it, especially since many app notes suggest using this equation for estimation. I will go with your calculator.

    Once again, thank you very much, John.

    Best regards,
    Malek

  • 0 in reply to Malek Hattab
    TI__Mastermind 36770 points

    Hi Malek,

    You are welcome. Glad I could be of assistance.

    Thanks,

    John