• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 46 subscribers
  • Views 283 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC9881: Not generating the correct output voltage

Moritz Speidel
Prodigy 20 points
Part Number: DAC9881

Hi,

i am using the DAC9881 to generate 0V-10V DC signals.

Attached you can find my schematics.

When sending 0x0570a  to the device and activating LDAC (Negative pulse with 10us length), the output changes from 0V to approx 150 mV. (Should be 0.5V?).

If i send 0x03f0a3 to the device, the output voltage does not change. If i send 0x00000, the output changes back to the initial value (approx. 0V).

Also attached are two screenshots from the oszilloscope for both codes != 0.

Do you find any problems in my schematic which could explain this behaviour?

Best regards,

Moritz

  • 0
    TI__Guru 53453 points

    Hi Moritz,

    I do not see anything obvious.  Can you confirm that the VREFHF pin measures 5V? Can you confirm that all of the supplies are the correct voltage. Can you iterate through some major carry codes and see if there is a pattern in the voltage response? E.G.:

    0x00010

    0x00020

    0x00040

    0x00080

    0x00100

    ..etc...

    0x20000?

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 20 points

    Hi Paul,

    thanks for your reply!

    I triple checked all supply voltages at least at the corresponding caps as the pins are rather tiny. All of them are correct. Also the REFH-S is at the correct voltage (something around 5.02V).

    The image shows the codes and corresponding voltages.

    I dont really see a pattern except the voltage step.

    Also the Voltage is rather instable. (In the 0.1 mV range)

    Am i missing something obvious?

    As per my configuration, i tried to read out the last code in the register and it was always the same as the one i sent.

    Thanks,

    Moritz

    Edit 1:

    This is the footprint on the board:

  • 0 in reply to Moritz Speidel
    TI__Guru 53453 points

    Can you ensure that the RST, LDAC, and PWDN pins are at the expected voltages? I see you have the MCU connected to the SDO pin.  Can you read back the register to see if you are successfully reading back the voltage?

    A common problem is that the SDO and SDI lines get reversed.  Note that when our DAC documents names pins as SDO or SDI, we mean serial-data-in and serial-data-out (sometimes also slave-data-in/out).  Make sure that you that you have connected SDI to MOSI or SIMO, and SDO to MISO or SOMI.

  • 0 in reply to Paul_Frost
    Prodigy 20 points

    The SDO1-Line referes to the MOSI Pin of the MCU (a PI-Pico-board) and is connected to the SDI-Pin of the DAC, the SDI1-line is connected to MISO and should therefore be correct.

    I allready tried to read back the last code send to the DAC and it is correct. (I used an oszilloscope for this).

    RST is at 3.3V.

    LDAC is at 3.3V and PWDN is at GND (confirmed and also directly connected to GND)

    The Scope-screenshots show first sending 0x03039 (just a random code) and then sending 0 to read it back with the next clock cycles.

    For me the code seems fine, only the voltage level when reading back is a bit low (1.5V).

    I also measured LDAC pulse width and it is 21.2 us.

  • +1 in reply to Moritz Speidel
    TI__Guru 53453 points

    Is this on just one board? Have you tried a second board? Could something be damaged?

  • +1 in reply to Paul_Frost
    Prodigy 20 points

    Hi Paul,

    In the meantime i checked the second DAC on my board, it works fine. I thougt i fried it and therefore i did not check it...

    Thanks a lot for your help!

    Best regards,

    Moritz