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analogue & digital on opposite sides of PCB ?

Discussion in 'Electronic Design' started by Adam Seychell, Feb 8, 2010.

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  1. I'm designing a 120A 4 phase step down power supply, and require a 6
    layer 2OZ PCB to meet current carrying capacity requirements. There will
    be a mix of sensitive analogue and digital in my purpose built
    multiphase controller consisting a mixture of op-amps, discrete
    transistors, high speed comparators, ADC, DAC, programmable logic & a
    microcontroller.

    Is it feasible to separate analogue and digital components so they are
    placed directly on opposites sides of the PCB, and use separate
    non-isolated ground planes ?

    I am speculating that return currents from digital lines should only
    flow in the adjacent ground plane layer, and not interfere with
    subsequent ground and signal layers. For a 6 layer stack I am considering:


    [analogue components]
    --------------------------
    L1 analogue signal
    L2 ground
    L3 power (analogue)
    L4 power (digital)
    L5 ground
    L6 digital signal
    ------------------------
    [Digital components]


    L2 and L5 will be connected only in limited locations.


    Adam Seychell
     
  2. With bus bars for Vin, GND and Vout. After much head scratching, I
    decided on hand soldering 2 x 12mm copper bus bars in close vicinity to
    the power components. A single hole at end of each bus bar will provide
    termination to 25mm^2 cable lugs and the like.

    The gate driver ICs are right up against the MOSFETs, allowing logic
    level PWM signal to go off to the controller circuit some distance away.

    The power and signal stuff are physically separated by 2", but are on
    the same PCB. I was concerned about laying the digital components on the
    opposite side to analogue components in the power supply controller section.
     
  3. I think he needs to move his Analog Power layer(L3) to the Top (Or
    Bottom). Inner layers for high power stuff results in higher copper
    temps, he may wind up delaminating the board. Plus, mounting the Buss
    bars may be easier.

    Cheers
     

  4. [analogue components]
    --------------------------
    L1 analogue signal
    L2 ground (digital)
    L3 power (analogue)
    L4 ground
    L5 ground
    L6 power (digital)
    L7 ground (digital)
    L8 digital signal
     
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