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ADS1115 Unused ALERT/RDY pin

Tim Wucher
Prodigy 20 points
Other Parts Discussed in Thread: ADS1115

Good day,

I would like to ask the following two questions regarding the ADS1115 ADC:

1) Due to space limitations our application does not allow the use of the ALERT/RDY pin. If this pin is unused, can it be left floating, must it be connected to VDD or GND and if so what resistors are suggested?

2) The ADS1115 is to be used to measure the output of a Wheatstone bridge (R = 2500 Ohm) with output levels of +-100 mV. Can the ADS1115 be used to amplify and convert this signal without pre-conditioning op-amps?

Your advice is much appreciated!

Thanks,

Tim

  • 0
    TI__Guru** 113765 points

    Hi Tim,

    The ALERT/RDY pin is an output pin, so you can safely let this pin float. As to making the bridge measurement, you can make the measurement as long is you have not violated the absolute input range for the ADS1115.  However, there are a couple of things that may work against you.  One is the low impedance of the inputs at high gain.  At maximum gain (+/-256mV) the input impedance drops to 710k ohms.  This current path will introduce a small error in the measurement, but may not be much at the 16-bit level.  The bigger issue may be total noise/drift in the measurement as the measurement itself cannot be made ratiometric (where noise/drift effects cancel).  Again, this may not be that significant at the 16-bit level, but it is of something to be aware.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points

    Hi Bob,

    Thanks a lot for your help. Your professional advice is much appreciated!

    Regards,

    Tim