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ADS1257 Single ended measurement

Piotr Koziol
Prodigy 20 points
Other Parts Discussed in Thread: ADS1257, ADS1256, ADS1255

Hello,

I have a question about single ended measurement with ADS1257. I know this ADC is very fresh, maybe this is the reason it has a basic pdf datasheet.

1) Which input pin is supposed to be used as a 'ground' reference for single ended measurement ? AIN3 ? In ADS1256 you have been advising to use AINCOM for this purpose. 

2) Can the differential method can be used with one input pin shorted to ground ? (AIN0 - input ,    AIN1 - ground          ||||  AIN2 - input, AIN3 - ground). Will it influence the measurement's accuracy ?

I assume all the digital communication and registers are the same as in ADS1256, am I right? 

I'm forced to use QFN because of the limited space on board.

Thank you in advance,

Best regards,

Peter

  • 0
    TI__Mastermind 44680 points

    Hi Peter,

    Welcome to the TI E2E Forums!

    Yes, this is a relative new device and an updated datasheet should be available within the next month or so. Feel free to use the ADS1255/6 datasheet as a reference in the meantime, as these are very similar devices.

    1) You can reference any input pin you like for the "ground" reference. Simply configure the positive and negative inputs pins in the MUX register. Performance-wise, it shouldn't matter which pin is your common reference...(For differential measurements, you might find that the AIN0/1 and AIN2/3 input pairs are ever so slightly better matched, but even then I doubt this will have an observable effect on the results.)

    2) Using differential measurements on AIN0/1 and AIN2/3, with AIN1 and AIN3 grounded should work just fine! You are only able to accept 2 single-ended measurements this way (compared to the maximum of 3 single-ended inputs), but there should be no effect on performance... As you said, even your "single-ended" measurement is still measured "differentially" - the only limitation is that the positive input is not able to go negative, so you never get any of the negative output codes (with fully-differential inputs you have potentially twice the dynamic range at your disposal).

    3) Correct, the communication and register settings are the same. The only difference is that you do not have as many inputs and GPIO settings to choose from in the MUX and IO registers.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    Prodigy 20 points

    Thank you Mr. Chris for resolving my doubts.

    Best regards,

    Peter

  • 0 in reply to Piotr Koziol
    TI__Mastermind 23275 points
    Hi Peter,

    I wanted to let you know that the complete datasheet of ADS1257 is online now.
    I hope you are still happy with the ADS1257 and are making good progress with your development.

    Regards,