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I have a kind of an open-ended question.

If I'm designing a board with a buck converter and have picked out my peripherals, and say for example I want to run my CAN FD interface at 1MHz baud and maybe a SPI signal at 1MHz, and I am now looking at power supply design.

I am looking at a buck switching regulator which has a switching frequency at 1.4MHz. Is there any big EMI issues with having the switching frequency so close to the frequency of my other signals running through the board? Should I aim at either a higher or lower frequency?

Pretty open-ended question, but I never really thought of it until I ran into it.

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  • \$\begingroup\$ This question is too open. If you have no coupling between the switching freq. and SPI, then it does not matter. But if you have a coupling, it might be best to keep the frequencies apart as far as possible. So what could be a good advice here? \$\endgroup\$
    – Stefan Wyss
    Commented Jun 23, 2020 at 17:46
  • \$\begingroup\$ @StefanWyss Hmm, maybe I can expand. The power from the buck converter would be used on the power plane to power both a microcontroller and peripheral devices. Expected stackup is sig - gnd - power - sig. \$\endgroup\$
    – Punchki
    Commented Jun 23, 2020 at 17:52
  • \$\begingroup\$ How much filter attenuation do you have inside that power distribution? \$\endgroup\$
    – Stefan Wyss
    Commented Jun 23, 2020 at 17:56

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If the regulator were that bad it'd screw up the board operation no matter what.

If you had a radio in there, then having a regulator switching at the RF frequency or a sub-multiple of it could be an issue (as could having a microprocessor clock close to a frequency you care about). But CAN and SPI aren't going to notice anything that won't generally make the whole board unable to function.

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