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CCS/TMS320F28054F: The typical resistance to GND for the ADC port A0

Arrow Wu
Intellectual 530 points
Part Number: TMS320F28054F


Tool/software: Code Composer Studio

Hi,

I'm using TMS320F28054F for HVAC system.

I use the A0 port for NTC sensor sampling. The NTC temperature sensor strategy is just a resistance divider to the ADC port.

However I found the A0 port's resistance to ground is not high impendance as other ADC ports.

Do the A0 port has a typical resistance to ground?

and is there anything for me to considering for using A0 port as a normal ADC port?

best regards

Arrow

  • 0
    TI__Guru 62975 points

    Arrow,

    The generic pin impedance characteristics are covered by the +/- 2uA Input current parameter in the table below. Note that the crossed-out pulldown and pullup conditions are incorrect. This will be updated. The typical ADC leakage is under 1uA.

    I believe that you are seeing the effects of RPD that is part of the VREFOUT Buffered DAC module on A0:

    RPD has a typical resistance of 20kΩ to VSSA.

    -Tommy