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ADS8326: Do you know any cause of a phenomenon that a DOUT data range is not output?

Kazuya Nakai59
Guru 20100 points
Part Number: ADS8326

 Hello guys,

 One of my customers is evaluating ADS8326 for their next products. They found very strange phenomenon in the evaluation. The phenomenon that  any data between 16242(3F72h)~16383(3FFFh) are not output from DOUT regardless the input voltage ("+IN" voltage - "-IN" voltage) as the attached graph. Also any data between 49024(BF80h)~53247(CFFFh) are not output but the graph is not attached. 

 They are using the circuit same as Figure 44 on page 27 in the device datasheet(SBAS343C). Also their evaluation conditions are that "-IN" terminal voltage is 0V^0.5V, "+IN" terminal voltage is less than "REF" voltage +"-IN" voltage, "REF" voltage is about 4.0V and VDD is 5V.

 Do you know any cause of this phenomenon? If you know, could you give me your reply?

 Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.

 ads8326_output_code_problem.pdf

  • 0
    TI__Mastermind 36170 points
    Hello Kazuya,

    I have not seen anything quite like this. However, if IN+ < IN-, then the output code will read back 0000h.

    Did the customer use the ADS8326EVM, or their own design? Can you provide a schematic that shows the input amplifiers, reference, and ADC?

    Also, the attached data appears to be a histogram. Can you explain how this data was generated? Is this a histogram generated from an input AC waveform? Would it be possible to provide a DC sweep, from 0V to Vref, to see if there are still missing codes?

    Thank you,

    Keith N.
    Precision ADC Applications
  • 0 in reply to Keith Nicholas
    Guru 20100 points
    Hello Keith,
    Thank you for you rreply.
    I see. I will ask them to give us the shematic and DC sweep test result.

    When the customer took DOUT data for the attached graph data, they input voltages which expected DOUT codes are about 16160~16430.
    In other words, though the customer input a voltage which expects 16300, the DOUT code is not 16300. I'm not sure what DOUT code is at the condition. But the DOUT code was not in the range of 16242~16383. They took DOUT data at the various input voltage in range of about 16160~16430 and made the graph.

    Thank you again and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 36170 points
    Hello Kazuya,

    So the output codes seem to get stuck when B14 changes from 0->1. This may indicate either a bad part or possibly a timing violation on the digital interface.

    1. Has the customer tried taking the data with a different ADS8326 device?
    2. Can the customer provide waveforms for /CS, DCLOCK, DOUT?
    3. Also, if they are reading data from the DOUT pin on the falling edge of DCLOCK, is the minimum 5nS hold time adequate for the controller (MCU, FPGA) they are using?

    Thank you,

    Keith N.
  • 0 in reply to Keith Nicholas
    Guru 20100 points
    Hello Keith,

    I asked them your questions. but I didn't get any answer from them at this moment. I will inform you when I get any answer from them.

    Thank you and best regards,
    Kazuya Nakai.