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Low Speed Audio DAC For 24-bit control loop

John Westmoreland43
Guru 13935 points
Other Parts Discussed in Thread: DAC1282

Hello,

I was over in:  http://e2e.ti.com/support/microcontrollers/c2000/f/171/p/303479/1059565.aspx#1059565 and it was suggested I ask the question in a couple of the other forums.

You can refer to the above link for background -  question is achieving 24-bit resolution and accuracy for a control loop - in this case for an EFC for an OCXO.  

Is there a low-speed Audio DAC that would work?  In the past the Burr-Brown PCM61P was used in this design - that was only 18bits but that design had a manual pot also for that reason I suppose.

I have looked at the available DACs - some are nice in that they have a glueless interface to the 28069 (McBSP) - but is it a good way to control a noise sensitive circuit like an EFC for an OCXO?

Alternatives are PWM (don't think the real bit resolution can be 24 with the 28069) and putting two 16-bit DACs together with the proper weighting for the resistors through a summing op-amp.

 I should add that the output voltage should be a held DC mode like the DAC1282 has.  

Suggestion appreciated.

Thanks,
johnw 

  • 0
    TI__Guru 63036 points

    Audio codecs are optimized for audio frequencies. They achieve their resolution by spreading quantization noise out of the audio band through oversampling (many times the actual sampling rate, like 128x). There are several issues for control applications (non-audio), among them delay through the converter and some may have artifacts at very low frequencies (close to DC).

    It may be possible to use an audio DAC for your application but please keep in mind that they are not designed or tested for uses other than audio (you must take care of out of band noise).

  • 0 in reply to Dominik Hartl11
    Guru 13935 points

    Hello D. Hartl,

    Yes - I was looking for 'DC Modes' in some of those - and didn't really expect to find any.  The PCM61P I believe is used in a design that is similar - I think that DAC did have some kind of DC mode - I haven't really been able to find a datasheet on that part since it has been discontinued.  Just curious to see how that would have worked.

    Thanks,
    John W.