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AD7194EBZ interface to external ADC

Question asked by Afgncaap on Apr 29, 2011
Latest reply on May 2, 2011 by LucaV

I'm trying to evaluate performance of the AD7192 in a sensor application.  I've  built a prototype board with my sensors and the ADC on it, with a SPI output. I'm trying to connect this board to the EVAL-AD7194EBZ that I have, which  should allow me to get data from the evaluation software, but I consistently get  a SPI error.


I submitted a question about this to ADI's technical support, and all I got back was "Due to differences in register configuration, the AD7192 evaluation board  should be used."  I then looked into the registers myself, and I found that, for the most part, all the registers are completely identical.  The only differences pertain to the AD7194 having more input channels, and no BPDSW.  Since I'm only using one differential channel, and I'm not using the BPDSW, it doesn't seem like this should be an issue.


I scoped the SPI lines on the eval board and on my board, doing an ADC reset.  The difference is that when using the eval board's ADC, the DOUT line responds periodically, and stays high most of the time.


On my board, the DOUT line stays low most of the time, and gives an occasional high blip not in tune with the clock (about 100us long, every 20ms), with or without running anything on the SPI.  The graphs below are what I recorded on the scopes for the two boards.  Line 1 is the clock, line 2 is the DIN line, and line 3 is DOUT.  [Edit: Line 4 on the second graph is the chip select.  It remained low on both boards, so that's not the issue.]


Obviously, I checked out the power supply, and everything seems normal on my board. My next step will be to try replacing the ADC on my board.  I'm not sure how I could have broken it, but I'm running out of options and I highly doubt the issue here has anything to do with the registers being different between the chips.


Any other suggestions?