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Need Help Selecting DAC

David Miller12362
Prodigy 10 points
Other Parts Discussed in Thread: DAC1220, PCM4104, PCM1795

I am designing a servo that requires >20-bit DAC resolution. I see there are many "audio" DACs that have this capability, but I am concerned about DC levels since often audio signals are high-passed. The servo just runs a basic PID loop so for me, being able to maintain a non-zero DC level is important. Should I be concerned about using "audio" dacs for this application? Are there audio DACs that could work?

 

I've looked at the DAC1220 which is the only 20-bit DAC not listed under the audio heading, but it has a 15ms settle time, and I need to update my DAC at ~30kHz.

  • 0
    TI__Guru 60826 points

    Most of TI's audio DACs use Delta-Sigma technology, which achieves high resolution through high oversampling rates (which distributes (and shapes) the quantization noise of the actual conversion over a large frequency band (many multiples of the audio band (Nyquist Fs/2)).
    One inherent aspect of this technology renders it sub-optimal for control applications: latency due to digital filtering: This varies by DAC model and can make it unsuitable for a PID loop (the latency is not part of the standard specification because it is not important for audio applications).

    If the interpolation filter latency of a delta-sigma DAC is acceptable, then the PCM179x series and PCM4104 products may be a good fit. The PCM4104 can be operated with an external precision +5V DC reference to improve output offset and drift, if desired.  

    If cost is not a critical factor, the PCM1704 may be a worthwhile candidate to consider. The PCM1704 is not interpolated and has no noise shaping. Settling time is also fast (200ns).

  • 0 in reply to Dominik Hartl11
    Prodigy 20 points

    Hello!

    I have a similar application as TS (servo steering, at least 20 bits, about 10 kHz), but now the recommended DAC (PCM1704) is discontinued. The suggested replacement is PCM1795. Is this circuit also an acceptable choice for servo control? And also, is there a reasonable way to connect it to an FPGA?

    Thanks in advance!

    /Camilla