ADM2687 Emission Problem

Document created by RAnslow Employee on Jul 3, 2015
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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,



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.


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,



This FAQ was generated from the following discussion: ADM2687 Emission Problem