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Custom design with ADAU1701

Question asked by cmoreno_uw on Apr 6, 2017
Latest reply on May 1, 2017 by KJBob

Hi,

 

Planning to use an ADAU1701 as an active crossover (3-way) as a first project.  I have several questions:

 

1)  What is the work flow when designing one's own custom board with an ADAU1701?  From the evaluation board schematics, it looks like I could simply place a 10-pin header connector exactly like J8 in the evaluation board (is it enough to connect only pins 1,3, 6, and 10?).  Is this a good approach for hobbyist projects?  I do have an evaluation board, so I have the USBi interface.

 

1-b)  What about just programming the EEPROM independently and then move it to the target board?  Would I need to design a separate board that only has the EEPROM and connects to the USBi?

 

2)  Do I need to bother with the WB (write-back) pin?  It's not clear from the manual (either the ADAU1701 or the ADAU1701-EVAL) whether I need to deal with it.  My design will be fixed and "set in stone" as far as the operation of the device goes  (I could still one day decide that I want to change some parameters, add more functionality, etc., but I would then connect it to my PC to reprogram it with the new design from SigmaStudio --- then, it will be again "set in stone").

 

3)  What's with the ADC_RES and the sampling rate?  I have no clue about why the resistor value depends on the sampling rate.  With the evaluation board, I just changed the sampling frequency from its default 48kHz to 96kHz, and then even to 192kHz and compiled and downloaded --- I didn't notice any change in the level (the volume) of the signal.

 

4)  The suggested low-pass reconstruction filter after the DACs has cutoff frequency of 50kHz.  If I'm using 48kHz sampling rate, doesn't that leave all of the out-of-band contents from 24kHz up?   I'm thinking that maybe the DAC oversamples, maybe all the way up to 192kHz, regardless of the sampling rate of its input data?  The datasheet does not say anything about this.   I would probably like to set 192kHz sampling frequency for my designs, but I'm not sure whether this will be feasible once I start adding more "non-trivial" processing blocks?

 

Thanks for any comments or suggestions!

 

Carlos

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