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ADS7955: Floating NC Pins?

bondk
Prodigy 30 points
Part Number: ADS7955
Other Parts Discussed in Thread: ADS7953, ADS7951

On pg. 7 of the ADS7955 datasheet, there is a note for the NC pins that states "Pins internally not connected, do not float these pins". Should these pins be tied to ground or some other known voltage? It seems strange that a pin labeled "not connected" would need to be connected to something.

  • 0
    TI__Expert 3175 points
    Hi bondk,

    We are in the process of updating the ADS7955 datasheet and will be clarifying the NC pin description, but here is the short answer:

    For the best design practices the NC pins and unused channels should be connected to ground.

    These pins are marked as no connect because they are input channels on higher channel count devices. This makes design changes, i.e. increasing the number of input channels, very easy because different channel count and/or resolution ADCs can be swapped out with no or minor PCB changes (e.g. switching the ADS7955 with the ADS7951 or ADS7953).
  • 0 in reply to Evan Sawyer
    Prodigy 30 points
    Hi Evan;

    Thank you for the clarification. If these pins are left floating, what effects will this have on the behavior of the ADC?
  • 0 in reply to bondk
    TI__Expert 3175 points
    Hi bondk,

    I would not expect leaving the pins floating to have any impact on the behavior or performance of the ADC. However, grounding the pins to the analog ground (AGND) helps to prevent any cross-talk between channels.