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MC33063A: Query about EMC conducted emission

Michele Galliano
Prodigy 10 points
Part Number: MC33063A
Other Parts Discussed in Thread: TPS54336A,

We are using your DC / DC converters. Code MC33063A in some case and TPS54336A in others. Input voltage + 24VdC. Output voltage + 3.3Vdc

Regarding the EMC conducted emission immunity it's more suitable a single dc / dc converter stage (+ 24Vdc -> 3.3Vdc) or an intermediate voltage level is required? (+ 24VDC -> 6Vdc -> 3.3Vdc) using for example an LDO at 3.3V as final output chip?

Thanks in advance.

Note:

Due to the pandemic, our working hours have changed. All the company staff is divided into 2 shifts. This week my team works in the morning 06-14 (Rome time UTC+2) so there could be some delays in the answers.

  • 0
    TI__Guru 59825 points

    Hello Michele,

    There is not a answer like one or the other is better in this case. It is totally dependent on the converter you are using, especially topology, power need, layout and so on and so forth.

    E.g. using a bunch of different capacitor values and sizes on the 24V input, the conducted emission on the input will normally reduce.

    Best regards,
    Brigitte

  • +1 in reply to Brigitte
    Prodigy 10 points

    Hallo Brigitte,Thanks for your reply,

    I agree on the importance of component placement, their value and type and the shape and length of the tracks on the pcb. I asked the question in that term because I have had schemes that apply an LDO after the DC/DC converter and others that instead use only the DC/DC converter, and I would have liked to know, in general, and assuming a pretty good layout in both cases, which of the two methods tend to provides better results, in reference to the EMC conducted emission

    Best regards,

    Michele

  • +1 in reply to Michele Galliano
    TI__Guru 59825 points

    Hello Michele,

    Really, I do not see how this question could be answered correctly. It depends on all the mentioned points which cannot be the same if you use only a DC/DC converter or a DC/DC converter and a linear regulator behind it. It is possible that the power needed from the mains is somewhat lower for the pure DC/DC converter solution as an LDO is dissipating the voltage difference times the current which could be pretty bad.

    Nevertheless, there is no answer which solution is the better one.

    Sorry, but power supply design and especially EMI design is an area where only the test in practice give the final answer. But this is then only for the one specific setup or requirements you are testing.

    Best regards,
    Brigitte