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ADS8588S: AGND and DGND

Y.Ottey
Mastermind 6145 points
Part Number: ADS8588S

Dear all,

I would like to ask a question about AGND and DGND.

Is AGND and DGND of ADS8588SIPMR separated internally?

Our customers want to know about the above when designing with this device.

Best Regards,

Y.Ottey

  • 0
    TI__Mastermind 45785 points

    Hi Y.Ottey,

    There is no connection between AGND and DGND on the device. As described in Layout Guideline section in ADS8588S data sheet, using a single common ground plane is strongly recommended. For designs requiring a split analog and digital ground planes, the analog and digital ground planes must be at the same potential joined together in close proximity to the device. 

    Thanks&regards,

    Dale

  • 0 in reply to Dale Li
    Mastermind 6145 points

    Hi Dale

    Thank you for your reply.

    I would like to ask additional question about your answer.

    "For designs requiring a split analog and digital ground planes, the analog and digital ground planes must be at the same potential joined together in close proximity to the device. "

    Regarding the above sentence, what are the concerns in designing the analog and digital ground planes separately in the following cases?

    1. When each ground plane has a different potential
    2. When each ground plane is not close to the device

    Best Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Mastermind 45785 points

    Hi Y.Ottey,

    You should connect the AGND and DGND to the same voltage potential +/-0.3V, otherwise you will violate some of the maximum voltage ratings of the product and potentially damage the device, a back-back schottky diode between AGND and DGND can be used to meet the requirement. If your each ground plane is not close to the device or the joint point is far away from the device, the analog and digital signal currents will have to take a longer path to return back to the device, they may interfere with each other, the sensitive analog circuity can be affect by the digital return currents, you will not be able to achieve the specified performance, also may violate the maximum voltage rating of the device.

    For more information on this topic, take a look at this FAQ thread: 

    [Resolved] [FAQ] PCB Layout Guidelines and Grounding Recommendations for High-Resolution ADCs - Data...

    Regards,

    Dale