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TMS320F2808: Is there a internal pull-up resistor on the ADC pin？

Seven Han
Intellectual 600 points

Part Number: TMS320F2808

hello，After the sensor connection is disconnected，ADCINB0 is equivalent to connect to the outside pull-down 3M resistor，Ideally, the ADC conversion value should be close to 0 at this point，But  there is a voltage of 0.5xxV on this resistor，I don't know whether this describ is right？Can you tell me how i get 0.5xx Voltage and how do you make ADC get 0? Is it caused by initialization?

Thank you.

  • 0
    TI__Guru 62975 points
    Seven,

    There is no pull-up on the ADC pin. 3MΩ is a fairly large resistance. Are you allowing sufficient time for the net to discharge before sampling with the ADC?

    Another factor to consider is that the internal ADC S/H capacitor may have some carryover charge from the most recent ADC conversion. You can mitigate this by converting a channel that is connected to GND (to discharge the S/H capacitor) before sampling the disconnected sensor net. Increasing the ACQ_PS can also give the S/H cap more time to discharge through the 3MΩ resistor.

    -Tommy
  • 0 in reply to tlee
    Intellectual 600 points
    Ok，thankyou。