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ADuM140x EMI

Question asked by ezmbi on Mar 20, 2013
Latest reply on Mar 21, 2013 by DaveC

Hello ADI support,

By comparing table 4-5 (1 Mb/s, 3.3V) with 6-7 (10 Mb/s, 3.3V) of AN-1109, emissions from the ADuM140x scale up with channel bit rate like:

 

30--230 MHz

45-28=17 dB/dec for the standard board

(45-16)-(28-11) = 12 dB/dec for the optimized board

 

230 .. 1000 MHz

53-36 = 17 db/dec for the standard board

(53-24)-(36-7) = 0 dB for the optimized board

 

1. If I am not wrong in interpreting the results, it looks like the optimized board does a better job at higher frequencies (> 230 MHz) than at lower frequencies, where common mode emissions dominate.

Can you explain this behaviour?

 

2. The optimized board barely meets CISPR 22 class B limits at 10 Mb/s in the lower frequency range. Now the ADuMx can reach 90 Mb/s.

Should emission levels scale up as stated above in the 30-230 MHz range, is it at all possible to meet class B EMC specifications with bit rates higher than 40 Mb/s up to the specified limit? Do you have any measurement data for these cases?

 

Best regards,

Maurizio

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