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ADS1241 sampling an input signal range over 5 volts

john winans
Prodigy 20 points
Other Parts Discussed in Thread: ADS1241, ADS1220

I am having trouble understanding the external voltage reference and its relation to the ACR's RANGE bit on the ADS1241.  I want to sample a voltage source that ranges from 0 to 5V.

I power the chip at 5V.  Seems to me that I'd want to set -Vref to Agnd and +Vref Avdd.  But page 12 of the data sheet says I *MUST* set RANGE to 1 for this.  Would not that limit me to 2.5V input signals?

Maybe I should ask the simpler question... How do I configure the chip to let me sample values from 0 to 5V?

-John

  • 0
    TI__Guru** 113765 points

    Hi John,

    This device is limited as you have discovered. Basically you will need to set AIN- to 2.5V and measure the difference and add 2.5V to the measurement.

    You could also take a look at our latest device the ADS1220.  This part will work more as you expect, but only has 4 single ended inputs.  You might find that two devices take up less space and can take data more quickly as it is single cycle settling.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points

    Bob,

    Thank you for the fast response.  That new device looks nice.  But I would have to have a pair in hand this week to make my deadline.  I don't see any stock anywhere.

    I and OK staying with the 1241s I have now as long as I can make them work.  I can conjure up 2.5V.  So... what then do I want to set the Vref values and RANGE to if I do that?

  • 0 in reply to john winans
    TI__Guru** 113765 points

    Hi John,

    You should be able to get ADS1220 devices from sample stock by clicking on samples on the device landing page.

    As far as the ADS1241, use 2.5V for reference (also can be used to connect to AIN- input) and Range 0.

    Best regards,

    Bob B