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TPS55010RTER Conducted Emmision

Kenneth Wood
Intellectual 490 points

Hi,

I am using the TPS55010RTER for a +5V galvanic isolated CAN bus supply. The transformer is generating an enormous amount of switching noise and I fail MIL-STD-1275 EMC test due to it. Is there a way to snub the transformer noise at all?

Thanks
Ken

  • 0
    TI__Mastermind 25570 points
    Hello Ken
    Lots of things can contribute to the EMI signature - here are a few things you can check

    Ground the core of the transformer to an AC ground on the primary or secondary - you need to experiment here. Copper foil with a conductive adhesive and a short lead to the ground point works well.
    Add a 'belly band to the transformer.
    Put the core gap on the centre leg only - gapping all three legs (which is cheaper of course) allows fringing flux to 'escape'
    Wind the transformer so that the 'quiet end' of the winding is at the outside - the 'noisy or switched' end is screened somewhat by the quiet end of the winding
    Minimise the leakage inductance of the transformer - reduce the source of the noise.
    Pay very careful attention to the layout - minimise any stray inductance which can cause ringing
    RC or RCD snubbers on the primary of the transformer can reduce the noise generated - at the expense of a loss of efficiency
    Arrange the layout so that the EMI filter is not 'bypassed' - transformer should be as far from the input to the filter as possible.
    PCB traces into the filter inductor should not form a capacitive bypass path - by running beneath the filter core for example
    Add a 'y' capacitor - from input to output - this will allow common mode noise to circulate within the PSU rather than having to take an external path.
    There is useful information on transformer design at www.ti.com/.../slua418a.pdf

    Regards
    Colin