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Can you clarify the EMI filtering of the ADUM5412?

Question asked by gvellet@west on Nov 28, 2017
Latest reply on Dec 4, 2017 by gvellet@west

Hi,

 

I refer to the ADuM5412 datasheet on page 26, figure 32. There is a ferrite bead in serie with the isolated GND of pin 13. What is not clear is where to connect the other isolated ground pins #16 and #23. In the figure 32, it looks like pin 13,16, and 23 are connected with a trace. But they are also connected to the ground plane named GNDiso. If I do that, I will effectively short the ferrite and nullify its reason to exist.

On the other hand, lets say the figure 32 is wrong, and I proceed to connect instead pin #16 and 23 on the right side of the ferrite which is the plane GNDiso. Now It may be wrong too !!, because on page 18 it is clearly said that pin #13, 16, and 23 are internally connected and they should be connected to a common ground.

I tried to make some sense of this situation by referring to a similar device  which is the ADM2582. In its Application notes AN1349 page 3, figure 2,  there is a very clear layout  that shows a solution somewhat in the middle on my 2 options where only 2 ground pins are shorted together, and the third one connects to the right side of the ferrite which is the ground plane. But nothing guaranties that the internal circuit of the ADM2582 is similar to the ADuM5412 and that the solution could be used.

 

Can someone help clarify what should be done for EMI filtering?

 

Thanks for your help

G. Vellet

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