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ADS8584S: Conversion and part speed

Part Number: ADS8584S

I am using the ADS8584S in a high speed analog acquisition system.  

The ADS8584S is set up with CONSTA and CONSTB tied together, CS and RD tied together, 5V power, parallel data mode and +5 and -5 input scale.

The ADS8584S works good and all channels are working.  I do have one concerning problem.  I am not able to get a data though put faster than 37KHz.  If I speed up faster the data from the channels gets shifted over so CH1 is 0 CH2 gets CH1 data and CH4 is lost.  I need to collect data at 20KHz and need some averaging behind the data as well so the ADS8584S was attractive with over a 300KHz bandwidth.

I have delays in clock cycles to ensure correct timing and have them set to the minimums that allow proper operation.

I would like to discuss why the throughput of the ADS8584S is so low.

    Definitely this ADS8584S ADC can support 330-kSPS sampling rate per channel with parallel interface, can you please show me your timing plot including CONVSTA/B, BUSY, /CS&RD and FRSTDATA? thank you.

    Best regards,
  • Dale, I am following the timing diagram for the parallel mode with CS and RD tied together.

    As for timing.  I am using a 18F87K22 running at 64MHz.  to make it work, I have to initiate the conversion like this:



    CONVSTA and CONVSTB are tied together, this seems backwards from the timing diagrams shown as they say to toggle low to start the conversion, but when I do that my data is shifted one channel over.  Same for if I remove the 15 cycle delay above, chan1 is moved to chan2 and so on and ch4 is lost.  I do not understand that.  

  • Also, to start the conversion and read in four channels is taking my processor 22uS. if I speed that up any, the data is shifted so chan1 is reported for chan2 ect. Not sure why this is. but 22uS is only 45KHz rate. no where near the 330KHz claimed in the datasheet.
    It will be good and clear to check if you can show me the timing plots with and without delay. Also, are you using dedicated parallel interface or GPIOs on this controller? Thanks.