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EMI problems with ADM2682E

Question asked by mike1100 on May 28, 2014
Latest reply on Jun 6, 2014 by mike1100

Hello

 

i implemented in our new product about 10 nodes with the ADM2682E.

The bus we use is a 4 wire bus full-duplex and terminated at it's ends with 120ohm.

 

EMI tests on the system shows that we have big problems around 400MHz.

AN-0971 and also AN-1109 were read after the first prototype was ready,

so i followed only the recommendations which were given in the datasheet (figure 41 REV B)

 

So my problem now is how should i go on.

First steps that i will try :

- implementing a 5V to 3,3V supply for the ADM2682E

- stitching capacitor but the calculation result of this will only be 27pF due to the fact that i've no place on the pcb

- pcb itself is a 4layer, is it better to change to a 6 layer

 

At the EMI measuring institute we try to solve it with Y-capacitors between GND and ISOGND, 5V and 3V3ISO.

The capacitors have 150pF, the result was good. But for the series it is not a solution.

 

Could you give me any advice ?

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