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DAC8830: Voltage drops in VREF and CS in the DAC8830.

Santiago Sierra Rios
Prodigy 20 points
Part Number: DAC8830
Other Parts Discussed in Thread: TIDA-01504

"I need help with the grounding connection of the DAC8830, as when connecting it to a microcontroller, I experience voltage drops in VREF and CS. Additionally, Vout shows no variation. I analyzed the data frame I sent via SPI using a logic analyzer, and it's correct. I suspect my issue is with grounding. What recommendations could you suggest?"

  • 0
    TI__Genius 9410 points

    Hi Santiago,

    Do you have a schematic you can show us? The DAC8830's AGNDF, AGNDS, and DGND should all be connected.

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 20 points

     

    I have used this configuration joining the grounds, I also tried separating the analog grounds from the digital grounds as a second option, leaving the GND of the MCU with the GND of the DAC, and the analog grounds separated, but I have not had any results, when I check the reference voltage It falls in half and does not present a variation when I send the data via SPI.

    In this image I can see the data that I am sending via SPI, which correctly reaches the DAC, but I do not get voltage variation

    "If you have a schematic of the connections, I would greatly appreciate it."

  • 0 in reply to Santiago Sierra Rios
    TI__Genius 9410 points

    Hi Santiago,

    Definitely keep all 3 of the grounds tied together. The signal you're sending looks good, and I don't see anything wrong with your schematic. Could you describe more the issue you're having with the reference voltage? The reference voltage should be supplied externally, so that collapsing could suggest a problem with your setup, since the device would not have that effect. In addition, when you say you verified that the data reaches the DAC, did you probe the pins? I would suggest probing with both the DAC ground and the MCU ground to make sure the grounding is not different.

    Here is an example schematic from the TIDA-01504 reference design.

    Thanks,
    Erin

  • 0 in reply to Erin Bowrie
    Prodigy 20 points

    My problem with the reference voltage has been solved. I switched to powering the DAC with an external power supply, and the voltage remained at 2.5 volts. But now my issue is that the CS doesn't rise to 3.3 volts, which is the voltage of the MCU output pins when high. If I measure the voltage of this output without connecting it to the DAC, it stays at 3.3 volts. As soon as I connect it to the DAC, the voltage drops to half. But there are no more elements between them, only the resistor you suggested in your diagram.

  • 0 in reply to Santiago Sierra Rios
    TI__Genius 9410 points

    Hi Santiago,

    When you measure the CS pin of the DAC without connecting the MCU, what do you get? From your schematic, it should be pulled up to 5V. The voltage going to 1.7V sounds like there's an extra resistor divider somewhere that you didn't intend. 

    If you're able to change it, I would recommend pulling CS up to 3.3V instead of 1.7V, so that your MCU and CS don't fight over the voltage. If your CS line is push pull, though, you can also remove R41 and see if that changes the voltage to 3.3V.

    Thanks,
    Erin