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ADS1294: High density PCB design with Digital and Analog Grounds

Prodigy 150 points

Replies: 2

Views: 60

Part Number: ADS1294

I'm interfacing a CC2652RB (digital) with the ADS129X (analog). Ideally, from a signals and manufacturing perspective, I would be able to place these chips on the same top layer and connect my digital and analog grounds through a single line, but I don't think that's possible given my application size constraints. Assuming I can reflow chips onto each side of the PCB, would my best approach to PCB layering be:

  1. Top: Digital signal
  2. Layer 2: Digital Ground Plane
  3. Layer 3: Analog Ground Plane
  4. Bottom: Analog signal

The only other option would be to place the chips on the top layer, and place their supporting circuitry (capacitors, resistors) on the bottom using vias. What would you recommend?

  • Hi Matt,

    Instead of having analog and digital ground plane on 2 different layers, you can have both of them as a single ground plane on Layer 2 (see below) and use Layer 3 for your power supplies routing. 

    1. Top: Digital signal
    2. Layer 2: Analog/Digital Ground Plane
    3. Layer 3: Analog/Digital Power Supply 
    4. Bottom: Analog signal

    I would recommend to have all the critical input signal path components on the same layers. Please refer to ADS1298 datasheet (section 12) and the  ADS1298 EVM User Guides for layout examples. 

    The following threads may help as well :

    https://e2e.ti.com/support/data-converters/f/73/t/723695?tisearch=e2e-sitesearch&keymatch=%20user:359756
    https://e2e.ti.com/support/data-converters/f/73/t/764514?ADS1298-Decoupling-Bypassing

    Thanks.

    -TC

  • Hi Matt,

    I totally agree with TC about the grounding. I just dropped in to add one important issue, the clock input for your CC2652RB. I prefer to put the crystal next to the microcontroller and possibly away from the edges of the PCB. Additionally, the ADS129X is not totally analog. It is a mixed-signal IC. I prefer to use the PCB layout recommended by the user manual for better performance.  

    Good luck

    Mes 

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