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a simple question about the ADS1259 evaluation board

You li
Prodigy 170 points
Other Parts Discussed in Thread: ADS1259, PGA280, ADCPRO

I have one question about the 24bit ADC ADS1259 evaluation board. I plan to use it to measure the output of my DAC. However, my DAC output is from -5 V to 0 V, the ADS 1259 working is from 0 to 5 V.  So can I use this evaluation board to measure my DAC?  Is there any problem in hardware or software? thanks a lot!

  • 0
    TI__Mastermind 44680 points

    Hi You Li,

    Welcome to the TI E2E Forums!

    You would need to level shift the DAC signal to 0V to 5V in order to measure it with the ADS1259EVM.

    If you have a -5V supply rail, you could use it as the ground reference for the ADS1259EVM, which effectively performs the level shift operation. You would also need to use the 0V supply as the ADC's analog supply (0- -5 = 5V) and a -1.7V supply (-1.7- -5 = 3.3V) for the ADC's digital supply. This can be done, but you would need to be very cautious not to accidentally over-voltage any of the components on the ADS1259EVM or MMB0.

    A safer option would be to reference everything to a common voltage potential and use a buffer to level-shift the DAC output voltage!


    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    TI__Mastermind 44680 points
    Hi You Li,

    My apologies...I forgot about the PGA280 on the ADS1259EVM. My above response only applies in the case that you want to bypass the PGA280 and connect your DAC directly to the ADS1259.

    However, if you connect to the PGA280, then it will provide the level-shifting function and you can use a common ground reference. (Note you'll need to provide additional +/-10V supplies to the ADS1259EVM).

    Please let me know if you have any additional questions!

    Best Regards,
    Chris
  • 0 in reply to Christopher Hall
    Prodigy 170 points

    Hi Chris,

    Thanks a lot for your reply!

    In my application, we want to bypass PGA280 and directly connect to the input of ADS1259. It is because our measurement is for a high precision DAC (20bit 1 ppm accuracy) and the linearity of PGA280 is less than 1.5 ppm. 

    I would like to use the AVDD=0, AGND=-5V, and -1.7V digital supply for the ADS1259EVM.   If I change the power supply for both ADS1259EVM and MMB0, there is no over-voltage problem for any component,  right?

    What's more, do you think there is any other problem if I use ADS1259EVM to measure my 20bit DAC? Or any other better suggestion? e.g. any other type of device which is better to do my measurement?

    Thank you very much!

    Best Regards,

    You Li

  • 0 in reply to You li
    TI__Mastermind 44680 points

    Hi You Li,

    If you're careful to maintain the proper voltage potentials between all connections made to both the MMB0 and ADS1259EVM, then you shouldn't over-voltage any components. Still, I recommend looking at the MMB0 schematic to see how the MMB0 supplies power to the ADS1259EVM. You can find the MMB0 schematics here:

    I don't see an issue with trying to use the ADS1259EVM to measure your DAC, though it would be more ideal if both devices were located on the same PCB. Connecting multiple PCBs together can add significant parasitic impedance and have higher than normal noise performance. Try to keep connections between the PCBs as short as possible!

    It would be good if you were able to use the same reference voltage source for both the DAC and the ADS1259; however, due to the way you're planning to bias the ADS1259EVM, this may not be possible, since connecting the reference voltage directly may provide an over-voltage to the ADS1259.

    Note that, even though you are not using the PGA280, you may still need to supply the +/-10V supplies for the ADS1259 EVM to operate. However, these would need to be -15V and +5V (to be properly referenced to your -5V AGND supply). Oddly enough, the ADCPro software may not communicate with the MMB0 without these supplies. Removing the PGA280 from the ADS1259EVM and NOT applying these supplies may work; however, I'm not sure what exactly the software checks for when it starts-up. Just be aware that this may add additional complications!

    Best Regards,
    Chris