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TMS320F280041: F28004x - unconnected ADC inputs

Jens G
Intellectual 2765 points
Part Number: TMS320F280041

Hi TI Team,

I have a question regarding the unused ADC pins. In older devices it was necessary to connect a resistor to this pins which are not used. In new F28004x devices it is possible to let this open (see screenshot). Please can say something about the advantage and disadvantage of "no connect" and "tie to VSSA though...".

From PCB space and layout perspective the advantages of "no connect" is clear, but what are the side effects? What is with respect to floating effect to be aware of?

Thanks in advance and best regards,

Jens

  • 0
    TI__Expert 5050 points
    Jens,

    There is no problem to leave these floating, though there is one consideration. These pins have an AIO input functionality (as well as an internal pull up which can be enabled). If these pins are left floating then the AIO input function should NOT be selected (it is not by default). If the AIO was turned on and the input floating then there could be crowbar current on the input buffer which needlessly consumes a variable current. Note, if the internal pull up was also turned on in that case, then there would not be a problem either.

    So there is a dependency on software configuration of the device. If you do not have full control over the software implementation then the more conservative approach would be to use a resistor here. However since most applications do have control over their own embedded software, you can save board space by omitting these pull resistors.

    On other C2000 devices you may have used there were also AIO's in parallel and the same consideration would apply there, the specific device datasheet would need to be consulted.

    Best regards,
    Jason