Hi, I'm Jiyeon Choo. I have a question about PMP21495. This DC DC converter has a resonant frequency at 500kHz. The switching frequency you set is 300-700kHz. Is there a reason you set it like this?
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We set the resonant frequency and switching frequency high mainly because we want to shrink the board dimension to increase power density. Detail design considerations of this design can be found in the following Power Supply Design Seminar presentation.
When LLC resonant converter has large Lm/Ls ratio, the input/output voltage gain curve will get flat. In order to cover the gain range you need, you will have to have a wider operational frequency range. This is common in LLC resonant converter with high resonant frequency.