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ADC128S022: Data Anomaly on IN0

Cedrick
Expert 8270 points
Part Number: ADC128S022

Hi,

Good day.

Our customer is using the ADC128S022 and they notice this behavior on IN0:

"The problem we are facing with the component is that when we apply 1VDC and above on IN0 of the component, all the other analog I/O values are being pulled up by roughly 10-30mV. 

This does not occur if voltage is applied to any other pins at IN1-IN7.

The component is correctly decoupled.

Voltage was applied directly onto IN1. PCB routing is ruled out.

During our standard mode of operation, the chip select pin is periodically turned off and on.

Attached is a screenshot of our schematic."


Looking forward to your inputs.


Regards,

Cedrick

  • 0
    TI__Mastermind 31655 points

    Hi Cedrick,

    Does the customer measure the voltage at the input pins externally to determine this new offset, or do they just see the result in the ADC codes for the IN1-7 inputs? What is being used to apply the signal to the input pins? Are all of the input pins being supplied a signal when the shift in the inputs is recorded? Does the amount of the offset change if the VA voltage is increased or decreased? Does the size of the voltage on IN0 affect the offset seen by the other input pins?

    Thank you,

    Scott

  • 0 in reply to Scott Cummins
    TI__Expert 8270 points

    Hello Scott,

    Thank you for your response.

    Here's their feedback:

    "We measured the input pins and it did not show this offset.

    It is only showing on the ADC codes for IN1-7 inputs.

    A 1VDC voltage is being applied to the input pin.

    All of the input pins are grounded through a RIS resistor. Our tests ran  up to 3VDC on the input. RIS is a 1.3kΩ resistor.



    We have VA tied to VD at the moment.

    The voltage offset increases as the voltage on IN0 increases. 1VDC on IN0 pulls the other inputs up to 15-20mVDC. 0.3VDC pulls up the other inputs up to 5mVDC.


    Regards,

    Cedrick

  • 0 in reply to Cedrick
    TI__Expert 8270 points

    Hi Scott,

    I would like to follow up o this request. Can you please let us know if there's any progress? Thank you.

    Regards,
    Cedrick

  • 0 in reply to Cedrick
    TI__Mastermind 31655 points

    Hi Cedrick,

    Thanks for your patience. I was out of the office at the end of last week, and I will get back to you on this tomorrow.


    Regards,

    Scott

  • 0 in reply to Scott Cummins
    TI__Mastermind 31655 points

    Hi Cedrick,

    I'm in the process of getting some additional help from a colleague with this. I expect to have some additional feedback this week.


    Regards,

    Scott

  • 0 in reply to Scott Cummins
    TI__Mastermind 31655 points

    Hi Cedrick,

    The FAEs involved with this opportunity have contacted me through email, and we are continuing the conversation there. I will update this thread once we've reached a resolution.


    Regards,

    Scott