This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS7128: outputs when component not powered

Part Number: ADS7128

Hi Experts,

May I ask for your confirmation? Our customer have issue with ADS7128. Customer said:
"This GPI extender is used for control of DC-DC in our design.
We added external pull-up resistor for AIN0/GPIO0 pin (100k).
We found that the ADS7128 brings the output down (LOW) when unpowered regardless of the pull-up resistor.
Please confirm that this component has it's outputs low whenever unpowered."

I hope you can help us. Thank you.

Kind regards,
Gerald

  • Hello Gerald, 

    I will look into this, I will have to check this on the EVM, thus give me some time. 

    I do not believe that the behavior of the ADC when the device is not powered is looked into. Looking at the datasheet, the analog inputs have ESD diodes that will turn on when the analog input voltage is higher than the AVDD voltage. From your description, it sounds as if this is what is occurring, as you mention that you "powered off" the device. when this occurs, the ESD will redirect the current the AVDD source. 

    How is the device being powered off? 

     

    Regards

    Cynthia 

  • Hello Gerald 

    I tested this on the EVM using AIN7/GIO7, see schematic below. When the EVM was not connected to anything, no power supply, and a DC signal was provided at the high side of R19, the voltage held, it did not get pulled down. I will note though that there an increase in voltage measured at AVDD. 

    The device defaults the input pins to AINP, which means at start up, after you power it down, all 8 input will behave as analog inputs until they are programmed otherwise. 

    My suggestion is to not power down the device. 

    Regards

    Cynthia

  • Hi Cynthia,

    Thank you so much for your detailed responses and help. I will forward this to our customer and will let you know if we need further help.

    Kind regards,
    Gerald

  • Gerald, 

    Quick question, are they using an isolator in the system?

    Regards

    Cynthia

  • Hi Cynthia,

    I still have not received any response from our customer and will confirm once I hear again from them. Thank you.

    Regards,
    Gerald