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