DAC isolation

Discussion in 'General Electronics Chat' started by Jim_2.0, Oct 11, 2007.

  1. Jim_2.0

    Thread Starter Well-Known Member

    May 14, 2006
    51
    0
    another question for you guys, been one of those days :( I have this DAC circuit, it is a MAX532 DAC. As you can see the DGND is connected to AGND and it seems that this must be the case. Except I want my +/-10V analogue output to be Isolated from my digital signals. How on earth can i achieve this? the reason for doing so is that the analogue output is powering transducers, which have the potential to introduce noise onto my digital lines.
     
  2. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    A small resistor or ferrite bead can help. But mostly you need to look at the return current flow from the transducer and make sure it doesn't pass by your sensitive signals. You can use a star ground or split plane method and have only one connection point between the grounds-- at the power source.
     
  3. John Luciani

    Active Member

    Apr 3, 2007
    477
    0
    If you want your analog and digital circuits to be *completely* isolated you
    can use opto-isolators on the digital lines and a separate power supply for
    the analog circuits. Are you sure you need that much isolation?

    As was mentioned you need to look at the return path for your currents and how
    much current is flowing. A large ground plane will have a very low resistance
    and will produce only small voltage drops. Keep your paths to ground short.

    (* jcl *)
     
  4. Jim_2.0

    Thread Starter Well-Known Member

    May 14, 2006
    51
    0
    I thought about using the opto isolator. I do have a seperate power supply available. the problem is that my clock for the SPI might run up to 1MHz, I dont think an opto will do this will it?

    I want the isolation because our analog out signal is directly controlling Variable Speed Drives for large motors. these units are notorious for noise and we have had problems in the past, I want all my digital circuitry completely isolated from the outputs. It is going into a heaby duty industrial situation where all sorts of gremlins may exists on the outputs.
     
  5. Jim_2.0

    Thread Starter Well-Known Member

    May 14, 2006
    51
    0
  6. John Luciani

    Active Member

    Apr 3, 2007
    477
    0
    Those Fairchild optos should work. There are quite a few choices for 1MHz signals.

    (* jcl *)
     
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