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UCC28700: SMPS

Raul Pelaez
Prodigy 20 points
Part Number: UCC28700

Hello,

Few Months ago I developed a Switch Mode Power Supply with the UCC28700, I followed the suggestions from the Datasheet to get a 5W 5V 1A as output, and it is working well. 

Now I want to get a 10W 5V 2A as Output with the same UCC28700 circuit I create before. is that possible? I don't know what to modify in the circuit to get those parameters. is there is any Information/Guide line about it that you can share with me?

See attached the schematic I used for my my first SMPS.

Thanks in advance...

Raul.pdf

  • 0
    TI__Mastermind 40350 points
    Hello Raul,

    I'm glad that you had success with your 5-W design.

    A 10-W design will have the same topology, however several components will have to change to accommodate the increased power level.
    You will not be able to "stretch" most of the existing components because the current stresses have doubled.

    The best way to design this is to follow the design procedure in the UCC28700 datasheet as you have for the 5-W design, except with higher Iout. A convenient calculator tool is available at www.ti.com/.../sluc408
    Also, consider refering to PMP4351 reference design for insight into the design.
    And you can try using Webench to generate a design.

    The main areas of concern will be:
    a) new transformer
    b) input bulk cap sizing,
    c) Main MOSFET size
    d) replace input R3 (10-ohm fusible resistor) with a real fuse
    e) output cap sizing
    f) main MOSFET snubber design (due to higher leakage inductance energy)
    g) current sense resistor R13
    h) possibly a bigger VDD cap C7

    A few other minor parts may have to change value as well, but the above list are the big items.

    I hope this helps you, and good luck with the new design.
    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    Prodigy 20 points

    Thank you so much for the information. I have a few questions for you which I'd be grateful if you can help me.

    I'm using the calculator you suggested me. But I don't understand some things.

    the first what I did was to change 1A to 2A in the design parameters. Then there are some values that I don't understand if I have to change it or I can leave it as it comes. (The values that come in yellow cells) And if I have to change it from where I have to take them.

    With those values I went to the Wurth Elektronik web page to see what transformer is the one that works for my design, but there they ask me for an Vaux which I don't know how calculate it.

    I'm following the SLUA653C Application Report, but there some values that were just assumed.

    As you can see I'm a rookie on SMPS designs. 

    If you have any other information you share to me that can help me through this process please don't hesitate to send it to me. I will be grateful to you. 

  • 0 in reply to Raul Pelaez
    TI__Expert 6080 points

    Hello Raul,

    The Aux voltage can be calculated based on your Nas and Vout and SLUA653C is a good starting point for your application design. I can help you understand specific equations which you do not understand.

    On the excel tool, every cell in yellow can be modified but if you do not know values like ripple or load step you can leave the original values but for example in Input capacitor section: row 6 is the calculated output cap value based on your output spec and you will have to reflect that in Row12 which is your chosen output capacitor.

    Regards,

    Sonal