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AMC1305L25: Noise coupling to the digital output of the IC

Arash Nejad
Prodigy 10 points
Part Number: AMC1305L25

Tool/software:

We are seeking technical support regarding the Sigma-Delta modulator IC "AMC1305." We are experiencing a noise issue in one of our products that we believe is related to this IC. It is being used to digitize three-phase 480V voltages. Intermittently, we observe noise coupled to the output of this IC.

Our questions are as follows:

  1. Does the AMC1305 have any inherent noise immunity features? Given that this IC operates in a fairly noisy environment, what are the best practices for decoupling noise from it? Are there any specific layout recommendations?
  2. If noise couples to the DVDD pin, what impact would this have on the IC's digital output?

We can provide additional measurement data to help further clarify the situation upon request.

  • 0
    TI__Expert 6405 points

    Hi Arash,

    Thank you for your question.

    Generally, the suggested layout examples for the AMC1305 can be found in the device's datasheet and EVM user's guide. Please see below. If noise couples on the power supplies, this could be seen on the output and lead to incorrect output values. To mitigate this, it is important to select proper decoupling capacitors. We include example decoupling capacitors in these documents for the power supplies that should be suitable for most applications. Have you confirmed noise on the DVDD pin?

    Could you please provide more background on your observed noise issue? Do you have schematics and/or layouts? What is the input signal?

    Please let me know so I can further help debug.

    Best regards,
    Eva

  • 0 in reply to Eva Mason
    Prodigy 10 points

    Thanks for confirmation,

    AS a matter  of fact, I was very much concerned about coupling of noise into the DVDD pin (and AVDD to some extent). Although we have the same layout that you have proposed, however, I'm still concerned the noise might have coupled to the AVDD/DGND pins due to large copper loop that has formed to provide 3.3v on the board. 
    We have used a 100nF decoupling cap in parallel with 2.2uF capacitor, both ceramics. 
    I would perform measurement on the AVDD and DVDD pins and will let you know if the same noise signature exists on those signals or not.

  • 0 in reply to Arash Nejad
    TI__Expert 6405 points

    Hi Arash,

    Great thank you for getting those measurements, please let me know what they look like. Do you have a schematic/layout we could check the copper loop you mention?

    Best regards,

    Eva

  • 0 in reply to Eva Mason
    Prodigy 10 points

    I would provide measurement of the DVDD and AVDD pins as soon as I captured those.
    Thanks

    Arash