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UCC28780: Maximum switching frequency

Niclas Samuelsson
Intellectual 490 points
Part Number: UCC28780

Hello TI-team,

I am planning on using the UCC28780 for an upcoming design. What exactly will set the upper limit on the flyback switching frequency? In the design examples for this IC, GaN switches are used, and are switched at around 400-500 kHz. I will use Si MOSFETs instead, so perhaps I should try to keep the maximum switching frequency a bit lower. What do you think? 


BR

  • 0
    TI__Guru 73475 points
    UCC28780 device itself frequency limit is 1MHz.

    UCC28780 converter fsw is variable depending on line and load. A better switching frequency,fsw, estimation for a converter can be done on MathCAD design file, that can be downloaded from www.ti.com/.../sluc644.

    A quick estimation for off-line universal ac input, low line full load to high line full load, fsw changes from low to high, about 1 to 2. The highest fsw is at high line with load when entering burst.

    For Silicon MOSFET, we suggest design low line (say 90Vac) full load fsw about 150kHz to 170kHz, then at full load high line (264Vac) fsw will be about 290kHz and 300kHz, and fsw at burst entering should be about 450kHz. We have a 45W EVM (UCC28780EVM-021) using Silicon MOSFET that can be referenced.

    Besides, an Excel design tool can be used for a design. The Excel design tool can be downloaded at www.ti.com/.../sluc664. In this tool, you can specify the low line and full load fsw.