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ADS8694: ADS8694

Part Number: ADS8694
Other Parts Discussed in Thread: ADS8689

Tool/software:

I am putting ADS8694 in one of my design.

The input is bipolar from -2V to 2V. and i am using the internal reference 4.096V with input range setting 0.625 x 4.096= +/-2.54V.

out of 18 bit data output 16 bit are changes as per input changes. but the 2 bits remains unchanged as input varies.

I am not getting why these two bits remains unchanged.

Please suggest the solution.

As per the last discussion, 

I am attached here, the schematic and the logic analyzer plot for the 2.255mV and 1500mV input for your reference.

In the logic analyzer data channel 0 is SDO, Channel 1 is SCLK, Channel 3 is SDI.

Please let me know which 18 bits should I consider as data.

 

  • Hi Swapnil,

    Can you please include the /CS line with the logic analyzer?

  • Hi Tom,

    See the attached logic analyzer plots with CS line at channel 4, SDO at channel 0, SCK at channel 1 and SDI at channel 3 for the voltage -0.4960 V and 0.5024 V.

    Please let me know which 18 bits should I consider as data output.

  • So...

    What mode are you trying to use with the ADS8689?  You have 3 16-bit transfers on MOSI with data on the 3rd 16-bit transfer that I don't understand.  On MISO, it looks like the ADS8689 is responding to what it thinks is a NOP command with SDO starting on the first clock of the second 16-bit transfer.  There appears to be a glitch on MISO (@19.5uS) as well.