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TMS320F28022: AIO voltage impact on other ADC pin

Strong ZHANG
Expert 3960 points
Part Number: TMS320F28022

Hi Team,

My customer are using ADCINB2/COMP1B/AIO10 for AIO function as output and ADCVINB3 for ADC function, they found that the output voltage of AIO10 will impact the voltage of another pin ADCVINB3 as below show, the peak voltage on ADCVINB3 is 1.7Volt and have similar waveform as that of AIO10, the waveform are measured when pin ADCVINB3 is float, if connect pin ADCVINB3 to a pull down resistor, then there will no this issue, question is why the AIO10 output will impact the voltage of pin ADCVINB3 without pull down resistor?

customer also did a test that using one GPIO pin for output, there is also have no this issue on pin ADCVINB3 when it is float.

ADCINB2/COMP1B/AIO10

  • 0
    TI__Guru 62975 points

    Strong,

    I assume that there is noise coupling between ADCINB2 and ADCINB3. This is not uncommon for floating input pins because very little energy is required to influence the charge on a floating pin. Coupling is more prevalent between pins that are near each other, and between pins that share resources such as reference supplies.

    Do note input pins with passive pulls enabled are not considered to be floating when not driven. Both internal and external pulls can provide a path for the coupled energy to be dissipated.

    I am not aware of any defined behavior for floating input pins on this (or any other C2000) device, and I would not consider this experiment to be significant.

    -Tommy