AD2428 A2B Bus I/O Filtering

Hello,

I am currently working on a consumer audio project using the AD2428. My question relates to the large EMI filtering section on the A2B Bus I/O sections (in the picture below). Are these filters only necessary because they are running in a car system, presumably alongside many other electronic systems, not to mention power lines, all of which create high frequency electromagnetic noise? Or are these filters necessary regardless of the application for coupling/decoupling or consistency do the potential requirement of having 15 m between nodes? If these filters aren't necessary to have for a non-noisy environment, it would be nice to shed the weight because it would reduce board size, complexity, and cost.

A follow up question to this would then be, if these filters aren't just for the high noise automotive environment but are in fact necessary no matter the end application, is the filter section circled below (from the EVAL-AD2428WD1BZ schematic) tuned to an input of 8 V, which is the output of the LTC3121 without the jumper installed? Or would a DC input of ~5V work.

Any help would be greatly appreciated.

Thank you,

Alex

  • 0
    •  Analog Employees 
    on Sep 29, 2020 2:19 PM 2 months ago

    Hi Alex,

    Apologies for the slow response.

    You are absolutely right. The current A2B filter network is optimized for automotive applications, tuned well to work with unshielded twisted pair cables of long length running in the car.

    For consumer applications, it is certainly possible to optimize the filter design (or even remove some too) and yet meet the target requirements. However, we’ve neither designed a dedicated filter network for such use case, nor validated it with some specific tests.

    If you could share more details regarding your use case: number of A2B nodes, cable lengths, overall A2B network length, etc., we could look into recommending some filter changes, while minimising EMC risks.

    The decision to remove/incorporate the various filter elements would be driven by the EMI/EMC requirements. Furthermore, it´s important to note that these requirements vary from use case to use case, and therefore, a “one size fits all” approach is not applicable. The circuitry that we propose by default, and that we expect customers to adhere to, is designed to meet the most stringent Automotive EMI/EMC requirements.

    I hope this helps.

    Best regards,

    Maikel

  • Hello,

    Thank you for your response and sorry for my late response. 

    The current use case is going to be for a home audio system. At spec there would be 3-4 A2B nodes that could be utilized in a surround sound manner. There would be up to 4 amplifier slave peripherals connected at each A2B slave node. I wouldn't think that the distance between nodes would be much more than 30 feet.

    The reason I ask about removing the EMI filtering is because a home environment is likely to be far less noisy than a car environment, so I am not sure if much EMI filtering would be necessary, and if some is necessary I would think a more basic filter would suffice.

    Thank you,

    Alex

  • 0
    •  Analog Employees 
    on Oct 14, 2020 9:43 AM 1 month ago in reply to ABatts

    Hi Alex,

    Thanks for the additional details. We will contact you privately via email to share possible EMI/EMC filter optimization recommendations to better match your system requirements. 

    Best regards,

    Maikel