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VREF setting on ADS1296 when using +/-2.5V supplies

Eduardo Rey17
Prodigy 230 points
Other Parts Discussed in Thread: ADS1296

Hello I am using the ADS1296 with bipolar supplies +/-2.5V.   So AVDD = +2.5V, AVSS = -2.5V.  There are 2 possible settings for the ADS1296 voltage reference (VREF) in CONFIG register 3 bit 5.  

a) If bit 5 is 0 = VREFP is set to 2.4V

b) If bit 5 is 1 = VREFP is set to 4V (use only with a 5V analog supply)

Questions:

Q1) Which setting should I be using to maximize the input dynamic range of the AFE?

Q2) When the datasheet says 5-V supply, do they mean +/-2.5 or 5V?

  • 0
    TI__Mastermind 38745 points

    Hello Eduardo,

    Great questions!

    1. The input referred noise level dictates the smallest signal that you can measure and with the ADS1296, it will not change with the reference voltage. The largest input voltage that you can measure is the reference voltage. Since dynamic range is defined as the ratio of largest to smallest signals, a higher reference voltage provides for more dynamic range.
    2. The +/-2.5 V bipolar supply qualifies as a 5 V supply. Basically the reference circuit is powered by the analog power supply and for the reference buffer to be able to generate 4 V with respect to AVSS it needs a 5 V power rail.

    Regards,

    Brian Pisani 

  • 0 in reply to Brian Pisani
    Prodigy 230 points
    Thanks for your responses, see clarification questions below:

    1. Ok thanks for clarifying
    2. Since the +/-2.5V supplies qualify as 5V supply can I use the 4V reference option or can I only use the 2.4V?
  • 0 in reply to Eduardo Rey17
    TI__Mastermind 38745 points
    Eduardo,

    Yes the 4 V reference is measured with respect to AVSS so you may use it with the bipolar option.

    Brian