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SN65HVD1781-Q1: EMC CE current test fail

Chase Jeong
Mastermind 7455 points
Part Number: SN65HVD1781-Q1

Tool/software:

Dear TI experts,

My customer failed EMC CE current test of their product using SN65HVD1781-Q1.

1) Average and peak values are exceeded in measuring CE Current in 80~90MHz bandwidth.

2) Max exceeded value of peak is -6dB, max exceeded value of average is -6dB (did not save measured data)

3) Exceed values are disappeared if RS485 communication is disabled.

4) Customer uses extended cable for RS485, and symtoms are different regarding to the location of cable.

5) Communication setup : 115200 baud rate, 200ms communication period.

Here are my questions;

1) Is there any specific guidelines for EMC CE current test?

2) Could you advice for have more margins to pass the test?

I attach the test results and schematic.

CE-S_Add signal line, Add GND.pdf

CE-S_Add signal line, Remove GND.pdf

CE-S_All bandwidth.pdf

Best regards,

Chase

  • 0
    TI__Guru 72771 points

    Chase,

    I'm not too famillar with the testing you are doing but how long is the cable they are transmitting across?

    Do you have a block diagram of their bus?

    Potentially I would think a common mode choke on the transmitting node may help a little bit if the issue is related to EMC but can you explain a little bit more on what EMC CE current testing is?

    Other potential things that can help for emissions is split termination to help stabilize the common mode voltage. 

    -Bobby