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ADS8327 - unlinear response - shifts within narrow input voltage ranges.

Other Parts Discussed in Thread: ADS8327, TMS320F2808

We are currently experiencing some problems with the ADS8327 16 Bit 500KSPS Serial ADC.

They work perfectly for a period of time, after a while some of them exhibit small shift in their voltage-to-digital response.

For example - If the input a is a very linear voltage ramp - at some point, the digital output will exhibit a small rapid change (like if one bit was toggeling inappropriately), i.e. shift out of spec, and come back on tracks after a few millivolts increase on the input.  

Has anyone already experienced this kind of problem? 

 

  • Hi Jean-Philippe,

    Welcome to the Precision Data Converter forum!  Can you possibly tell us where you see this linearity jump on the ADS8327?  If you could provide the digital codes (conversion results) from the linear sweep that would be great.  If you can also provide the details of the top side marking on the device, we could check over the QC logs to see if anyone has had a similar experience.

  • Please find below acquisitions before and after the ADS8327, i.e. analog signal acquired with a 6 ½ digit meter and the related ADC output.

    Both signals are roughly put to scale (in Newton as we are measuring the output of a force sensor, 1200N/4096mV for input, 1200N/216 for output) to be plotted on the same graph.

    Although the input is linear, the output exhibit variations of about 80 ADC values.

    It is no shown on the graph, but as the input is decreasing further, the output jumps back to the initial trend.

    Acquisition rate is 5 kHz. SPI clock is 5 MHz. Acquisition is done through a TMS320F2808.

    Replacing the ADC solves the problem, but does not give the reason why.

    The ADC step amplitude is different among the three ADS8327 showing this behavior.

    On one of them, the problem appears 2 times within its range.

    http://e2e.ti.com/cfs-file.ashx/__key/CommunityServer-Discussions-Components-Files/73/8865.ADS8327-problem.docx

    The impacted chips are marked TI ADS 8327I 826H 

     

     

     

     

     

  • Hi Jean-Philippe,

    Let me know which package option for the ADS8327 (the TSSOP or the QFN) you are using and I'll send you some replacement devices.