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UCC28704EVM-724: UCC28704

Arvind Kumar
Prodigy 60 points
Part Number: UCC28704EVM-724
Other Parts Discussed in Thread: UCC28704

Tool/software:

Hi TI Team,

My design specification are same as EVM but output current is 2.5A for 5V. Please answer my below question

1) Can I use same transformer (750315841) for my application?

2) What changes do I need to do in existing EVM board to get desired output?

3) What is Power Rating of transformer, what is current rating of secondary side?

4) I have downloaded UCC28704 Design Calculator excel but seems like that prefilled data is not matching with EVM design, Can you please share Design Calculator or Calculations for EVM?

Thanks.

Arvind 

  • 0
    TI__Guru* 82536 points

    Hello,

     

    The EVM was design for 10 W and your design is for 12.5 W.  This is actually 25% more power than the EVM was design for.

    1. It could function in your application but I am not sure how the transformer will behave reliably in your design with increased peak and RMS currents. You might want to check with Wurth to see if the transformer can work with a 12.5 W output.

     

    1. Changes required to get the design to work reliably at 12.5 W.
      1. Transformer design for 12.5 W application, turns ratios would remain the same.
      2. All components would have to be changed to handle higher peak and RMS currents
      3. The size of the current sense resistor would need to decrease to control the correct peak current.
      4. The following link will bring you to an excel design tool that will calculate the peak and rms currents of all components used in the design. It will also calculate the power dissipation of the components used in the design.  You can use this tool to check/select the components used in your design.
        1. https://www.ti.com/tool/download/SLUC603

     

    1. The transformer was designed specifically for the 10 W EVM application. You might want to check with Wurth to see if it can handle more power. 

     

    1. The EVM was released 9 years ago. However, I thought it matched the EVM.  Could you tell me what is different?

     

    Regards,

  • 0 in reply to Mike O'
    Prodigy 60 points

    Hi,

    1) Can you please provide contact details from wurth electronics for this transformer?

    2) I found some difference in excel sheet and EVM data that I have listed below

      Input in Design Sheet Data from Datasheet Remarks
    VFDA 0.8V 1V For HD06-T bridge rectifier Vfa is 1V from datasheet
    Choosen Np/Ns 12 13 Chosen turn ratio from excel sheet are not matching with XFMR datasheet
    Choosen Na/Ns 3.3 4

    Regards,

  • 0 in reply to Arvind Kumar
    TI__Guru* 82536 points

    Hello,

    Presently I do not have a Wurth contact but found there contact information below at their web site.

    Contact Us via E-Mail: shopOnline@wurthusa.com

    Customer Service Phone: @ 1-800-WURTH-USA (1-800-987-8487)
    Our Customer Service hours are: Monday – Friday, 8am – 8pm EST

    In regards to the excel tool.  These are recommendations and the design should try to get close to them.   When it comes to transformers getting exact turns ratio to match the calculations are difficult. 

    The calculations for selecting Np/Ns and Na/Ns are correct in the excel tool.  It is recommended that you use a turns ratio in your design that equals the calculation or is less than what the tool calculates within reason.

    The designer of the EVM designer chose a transformer with a Np/Ns of 12 knowing that it was close to the calculated value and less than the calculated values. 

    The designer of the EVM designer chose a transformer with a Na/Ns of 3.3 knowing that it was close to the calculated value and less than the calculated values.

    Regards, 

  • 0 in reply to Mike O'
    Prodigy 60 points

    Hi ,

    1) Thanks for the contact information.

    2) Designer have chosen transformer with Np/Ns =13 and Na/Ns = 4. So that is not equal to the calculation or is less than what the tool calculates within reason.

    Thanks.