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LM5146-Q1-EVM12V: EMI filter

Part Number: LM5146-Q1-EVM12V
Other Parts Discussed in Thread: LM5146-Q1

I checked EMI filter in LM5146-Q1 datasheet and the one implemented in LM5146-Q1-EVM12V board with CISPR25-C5 requirements (around 63dBuV)

Can you confirm two pi stages (the one for diff mode and the second for common mode?)

For the second stage, the 33uF polarized doesn't respect the Cd > 4*Cin.

Globally, could you give explanations with this EMI filter please?

Thank you for your help

  • Hi Romain,

    The damping cap should be 3-4 times the derated value for ceramic capacitance (where effective capacitance decreases with voltage - check the capacitor datasheet or vendor inline modeling tool (e.g. simsuring from Murata).

    More generally, the DM stage provides LC filtering of the fundamental and lower order harmonics. Meanwhile, the common-mode choke attenuates common-mode noise. The ferrite bead also provides high-frequency attenuation from a DM standpoint. For more detail, see parts 15 and 16 here:

    See also this e-book on EMI for further context: