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ADS1292: What happens if unused analog inputs float? Why the recommendation to tie them to VDD?

Eamon Egan
Prodigy 50 points
Part Number: ADS1292
Other Parts Discussed in Thread: ADS1291,

I am doing a circuit with ADS1292 where I don't know if the second channel will be used.

In case it is used, I would rather not add extra parts and add trace length to the input nets, just to pull the pins up if they aren't used.

Anyway, whether they are used will depend on what the board is connected to.

What (bad things) might happen if I leave IN2N/P or IN3N/P floating instead of connecting them to AVDD?

(See datasheet page 12, note 1)

Thanks,

Eamon Egan

  • 0
    TI__Guru 66246 points
    Hello Eamon,

    Generally, we recommend tying unused inputs to some supply voltage in order to minimize any leakage current to/from the device. It also reduces the possibility of unwanted noise from coupling into the part. In most cases, I think the effects of leaving the pins floating are relatively minimal, but we recommend this as a best practice to ensure the optimal performance of the device.

    As we've discussed earlier, you can still write to the CH2SET register, even if you are using ADS1291 instead of ADS1292. In that case, I would recommend that you at least configure the MUX for channel 2 as an input-short when the inputs are not used.

    The IN3P/IN3N pins are shared with the respiration modulation signals that are generated in the ADS1292R version. For ADS1291 and ADS1292, this feature is permanently disabled, so you must write 0x02 to the RESP1 register.

    Best Regards,