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ADAU1772 DC coupled DAC and ADC inputs

Question asked by rpmarchand Employee on Jul 18, 2016
Latest reply on Sep 28, 2016 by DaveThib

I have a question in regards to the ADAU1772.  I want to use the codec in a DC coupled application with the converters.  What I am trying to do is use the talkthrough mode of the part to pass the input from ADC0 to DAC0.  I’ve made a few modifications to the board (eval board) too which include:

 

  • Removing and shorting C2, C1
  • Removed C34, R41
  • Open J11

 

The idea was to remove the MICBIAS and use a DC coupled input with a 2.0V to 0V sensor.  This looks like it should be well within the ADAU1772 ADC range with 0dB gain on the PGA; from the datasheet it looks like with VDD=3.3V it should be 2.54Vpp.  For the purposes of experimentation I’m using a static 0.85V supply to drive the input of the ADC.

 

I am trying to output this to DAC0 (which I’m guessing is HPOUTLP/LOUTLP).  I configured the part in SigmaStudio to be in talkthrough mode.  I made no other changes to the ADAU1772 DAC output (it looks like I shouldn’t need to). 

 

I can’t seem to get anything out of the DAC.  Did I miss something obvious; attached is my SigmaStudio program.  I expected with the gains all set to 0dB on the PGA, and 0dB on the DAC that I should see basically the same input from the ADC back on the DAC (with some added errors but still pretty close). 

 

Any feedback into what i have missed is apprecaited.

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