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AD5429: DAC does not start up correctly sometimes

I have a problem that AD5429 can not start up correctly. The start up fails once or twice every 10 times power up.

In that case, DAC output does not change even tough applying any command and power up command. Does not respond to program (Clear DAC output to zero scale - 0xBXXX) and hardware reset (~CLR pin to 0). DAC use both channels: 1) as a programmble gain element; 2) standart unipolar mode. If DAC start correctly, work both channels, reset and correctly responds to commands from the microprocessor. Please refer to the attached my schematic and let me know if there are anything that need an improvement.

  • Hi ,

    Few questions:

    1) Can you please specify the power sequence used during power up? (VDD, VREFB, RFBA)

    2) When the device does not start up properly, what are the outputs of the two DACs? are they are zero scale?

    3) What is the range of Vin applied to RFBA?

    4) Have you tried testing if not applying Vin and disabling will result to consistent and successful power up?

    5) When the device does not start up properly, have you tried checking if readback function works? Just want to make sure that the communication block works.

    Cheers,

    Ivan

  • 1) Vref from High Precision Reference (+2.5V). +5V supply shown in scheme below.

    2)

    • On the 1st output DAC symmetrical impulse with range from +12V to -12V or midscale (pin VrefA).
    • On the 2nd output DAC zero scale or midscale.

    3) Symmetrical impulse with range from 1V to -1V.

    4) Tried, it does not start.

    5) Readback function doesn’t work.

  • Hi ,

    Can you please make sure that VDD is applied first, followed by reference voltage on VREFB, then lastly Vin on RFBA. If this is followed, please do observe if this still happens.

    Does your answer to my second question mean that when the problem happens, the outputs of the 2 channels could power up at different voltages?

    On my fourth question, what I was trying to say was starting from no power applied to DAC, just supply VDD then VREFB (no RFBA) then observe it eh problem still occurs.

    Cheers,

    Ivan

  • In case of incorrect start the outputs of the DAC have 3 values: 0, 128, 255. The both outputs power up at same voltages.

    Another moment. I have 2 identical boards, on which there is one chip DAC. There are cases: 1) when both DACs are not turned on 2) one of the two DACs is turned on 3) both DACs are turned on correctly.

  • Hi ,

    I gave 2 suggestions above, were you able to try them out? What were your observations?

    In case of incorrect start the outputs of the DAC have 3 values: 0, 128, 255. The both outputs power up at same voltages.

    Sorry I was not able to understand what you meant here, can you please clarify?

    Additionally, when debugging, can you make sure that only one DAC is connected to the system please?

    Cheers,

    Ivan

  • I tried both solutions:

    • VDD is applied first, followed by reference voltage on VREFB, then lastly Vin on RFBA;
    • start from no power applied to DAC, just supply VDD then VREFB.

    DAC starts incorrectly sometimes.

     

    In case of incorrect start the outputs of the DAC has one of three values: zero-scale, midscale and full-scale.

     

    If only one DAC is connected, the problem persists.