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ADM2687 Emission Problem

meir.mardechayev@phnx.co.il
on Jun 29, 2015

Hello ,

My name is Meir and I am DFAE.

One of my customers use the ADM2687 - Signal and Power Isolated RS-485 Transceiver.


They have an emission issue on ~180MHz frequency and 360MHz frequency (the second harmony) and they can't to pass the EMC/EMI sertification.

We suppose that this emission is a result of the oscillator of integrated Isolated power supply that his frequency is 180MHz.


Please see the attached files:

Schematics, PCB Layout, Radiated emissions results.

With the special probe we saw that the emission come from the chip.


Appreciate if you could help us to solve this problem.


Thanks a lot,

Meir


attachments.zip
  • 0
    •  Analog Employees 
    on Jun 30, 2015 10:04 AM over 5 years ago

    Hi Meir,

    We have some updated layout guidelines, with an application note released in the last 2 weeks. Please see the attached application note AN-1349.
    http://www.analog.com/media/en/technical-documentation/application-notes/AN-1349.pdf

    AN-1349 describes a number of EMI mitigation techniques, which are easier for the customer to implement.

    AN-1349 provides EMI mitigation techniques & layout advice specifically for the ADM2582E/87E.

    We recommend similar EMI mitigation techniques for the ADM2682E/87E, but the ADM2682E/87E will also have two additional ferrite components when compared to the ADM2582/87E.

    The attached ADM2687E layout sketch example shows the Ground 2 plane (green) connected outside the ferrites L1, L2, L3, L4.

    The ADM268E/87E has not been fully investigated and analyzed yet, but these notes should help.


    Best Regards,

    Richard

    attachments.zip