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ADE7912 / ADE7913 EMC layout recommendations for appliances

Question asked by rthinman on Apr 12, 2017
Latest reply on Apr 20, 2017 by Godson

We are designing an appliance with integrated power monitoring and I would appreciate some suggestions for meeting EMC and safety requirements (EN55014 and IEC60335-1).

 

I have read your AN-1332 and admire the PCB-integrated stitching capacitor: it is low inductance and inexpensive, as long as you are OK with a 4-layer board.  However, I'm not convinced I can use it in my application.  I don't have access to the IEC6052-31 standard being designed to in the application note, but from the application note I gather that a 0.4mm separation is sufficient insulation thickness for energy meters.  In my reading of IEC60335-1, which applies to appliances, the insulation thickness between AC mains and the low voltage side (reinforced insulation) must be >= 2mm.  That requirement cannot be satisfied on a conventional 1.6mm thick 2-layer PCB, much less a 4-layer one.  So the two ground planes cannot overlap to create a capacitor.

 

Some options I am considering are:

  1. Using a discrete Y2-rated stitching capacitor.  My dilemma is that SMT capacitors are not that long so I question whether they meet clearance requirements, but radial through-hole capacitors probably don't have the kind of high frequency performance needed to suppress those 383 MHz and 766 MHz emissions peaks.
  2. Putting the whole thing in a metal box.  Right now it is in plastic.
  3. Both of the above.

 

Do you have any recommendations based on tests you have run with the IC?

 

Thanks,

Rod

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