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ADS1263: AINCOM level shifter output

Rachael Parker
Prodigy 30 points
Part Number: ADS1263


Tool/software:

I am designing with the ADS1263 and want to you the level shift feature to output the (AVCC-AVSS)/2 on the AINCOM pin. I write to the POWER register to enable the level shift bias circuit (bit 2 = 1). I expect to see ~2.5V for 5V supply at the AINCOM pin but I do not. The pin appears to be floating. What am I doing wrong?

thanks, Rachael

  • 0
    TI__Guru 53796 points

    Hi Rachael Parker,

    The VBIAS behavior is pretty straightforward, so are you sure the command is executing correctly? Have you confirmed that you have successfully set other register settings, and it is just this particular bit that is not working? I assume the ADC is powered correctly and has either an external clock or the CLKIN pin is grounded to use the internal oscillator?

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 30 points

    Hi Bryan,

    I am using the Waveshare AD hat which I know is not supported by TI. I wrote code to read all registers so I can confirm I am writing them properly. I am using 5V supply and internal 2.5V reference for both REFP and REFN. I have tried TDAC input and results make sense. I have collected 100k reads with inputs floating and I see an input referred noise histogram centered at zero Vdiff. (Picture below)  

    Based on this I believe I am reading and writing correctly and the chip is functioning. I wanted to measure resistor thermal noise by connecting two resistors from AINCOM to AIN0 and AIN1 so I enabled the level shift bias  and set the input mux accordingly. When I probe the AINCOM pin I do not get 2.5V. I disconnected the jumper on the AD hat that shorts AINCOM to AVSS and I am probing the ADS1263 package pin just to rule out the AD hat board. I do see 2.5V when I probe the REFOUT package pin. 

    thanks, Rachael

  • 0 in reply to Rachael Parker
    Prodigy 30 points

    I found a big in my code. AINCOM is showing 2.5 V now. Thanks.