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LM5009 Conducted EMI

David Anderson78
Prodigy 50 points

At high Vin >70V it is not possible to use tantalum capacitors at the Vin pin to control conducted EMI, what solutions are recommended ?

  • 0
    TI__Intellectual 2320 points
    Hello David,
    You can probably try reduce the SW node slew rate and reduce the SW node spike by adding the resistor in series with the boot capacitor. This should help in controlling the conducted emission to an extent as high dv/dt of the SW node (high di/dt of the inductor current) and the SW node spike both contribute to the EMI.

    You can simply use an input filter if there is no constraint on the component count.

    Regards,
    Sourav
  • 0 in reply to Sourav.Sen
    Prodigy 50 points

    I am already using some input filtering as it is also required for immunity.

    I have tried delaying switch-on rise time  with a snubber across the catch diode which has reduced the EMI.

    Please indicate the acceptable range of values for a resistor in series with the bootstrap capacitor. Too slow a switch-on time will increase the switch dissipation significantly, and I also assume there is a circuit maximum limit for the effective ESR of the boot capacitor.

    The diode recovery time also seems to be relevant - the suggested part ES3D is around 20nS. Are there any diodes known to have better or worse EMI performance  with this IC or general recommendations for diode selection for high Vin/Vout ratio converters (in order to minimize diode recovery current) ?