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LM5155EVM-SEPIC: What to consider when LM5155EVM-SEPIC choosing switching frequency?

Part Number: LM5155EVM-SEPIC

As we can see on the user's guide. The switching frequency is 2.2MHz,

In the datasheet, the frequency can be 100kHz or 2.2MHz.

I want to know why does EVM choose this 2.2MHz? Is there any benefit or limitation of EVM or LM5155-SEPIC?

  • Hello Josh,
    Thanks for reaching out to us via e2e.

    Our EVMs are often built for a use case where many customers are interested in.
    This does not mean that the device itself would have any limitations in other constellations.
    The EVM is just an example application.

    A higher frequency allows for smaller external components but on the other hand it shows more switching losses / a lower efficiency.
    The user will need to define which parameters (output current/power, space, efficiency / thermal conditions, etc.) are most important.
    Also, EMI reasons or e.g. automotive applications (AM radio band) may limit which frequencies can be used.

    Best regards

  • Thanks for your reply.
    I have another question why flyback evm FSW is much lower(250kHz) than SEPIC (2.2MHz). Is that most customers prefer to using low frequency flyback?
    Or is there any benefit or limitation?

  • Hello Josh,

    In case of a flyback, the losses in the transformer and also the losses in the clamp (R-C-D network on the primary side of the transformer) are the limiting factor. So, for the flyback you may go up to around 440kHz, but above that, the losses will usually be too big.

    Best regards