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DAC80501：Using the DAC80501 as a DAC signal output,

bo zeng
Prodigy 10 points
Part Number: DAC80501


Tool/software:

Using the DAC80501 as a DAC signal output, the output signal is at the volt level. After a 1000x attenuation, the attenuated signal is affected by interference from the chip's control SPI signal. How should this interference be addressed appropriately?

  • 0
    TI__Mastermind 42273 points

    Hi Bo, 

    This issue is usually related to the PCB layout. How are you doing the 1000x attenuation? Do you notice noise on the DAC output before the attenuation? 

    Best,

    Katlynne Jones

  • 0
    Prodigy 10 points
    What are the specific requirements for PCB layout? Can you provide corresponding layout and routing examples? The attenuation is achieved using a resistor voltage divider, with 1MΩ and 1001Ω resistors. The noise amplitude before attenuation is about 10mV, and after attenuation, it is about 3mV.
  • 0 in reply to bo zeng
    TI__Mastermind 42273 points

    Hi Bo, 

    We do not have specific requirements, but there are best practices to avoid crosstalk/noise. Key recommendations are to have a solid ground plane, separating digital and analog traces when routing. This device only has one ground pin, but separating the traces while routing is still important. These two articles talk a little bit about it. 

    Grounding in mixed-signal systems demystified, Part 1

    Grounding in mixed-signal systems demystified, Part 2

    Microsoft PowerPoint - 5-Crosstalk on PCB Layouts

    It is also important for you to determine where the noise is entering the circuit. If the noise was only on the DAC output, then the 10mV would also see a 1000x attenuation. Given that is not the case you also have noise entering at or after the resister divider.

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Prodigy 10 points

    Modifications were made to the circuit by using a common ground for connections and incorporating the SPI signal lines into the inner layer for shielding, but there was no improvement in the output signal interference. The internal reference voltage of 2.5V was measured, and this reference voltage already exhibits strong SPI signal interference, with the interference reaching about 20mV. The reference voltage is also affected by interference from the SPI control signals. How can power supply interference be resolved? Should an external reference voltage chip be added? Or should appropriate signal filtering be applied?Looking forward to your expert advice.

    Best regards.

    Bo zeng

  • 0 in reply to bo zeng
    TI__Guru 55003 points

    Hi Bo,

    Could you consider using 2x DAC channels here? Any glitch on GND or the reference would be common to both channels, so if you use a differential output with a divider between them, you could see some improved digital feedthrough.  Ultimately, you need to impedance match your SPI and even consider using 50Ω termination to fully reduce the glitch.  In your case, I would probably implement external fitering to better improve your performance.  Is your signal dynamic? I would recommend that you route you output differentially with GND, then implement strong filtering, even if you critically dampen the DAC output (using a very large capacitance, like 10µF).

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 10 points

    Based on actual testing, it was found that the issue was caused by interference from the remote SPI on the DAC chip. The controlling microcontroller is located on another circuit board, and the two boards are connected via an FPC cable. After adding an anti-interference ferrite bead to the FPC cable, the interference in the DAC section was significantly reduced.