• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 48 subscribers
  • Views 474 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

ADS1261: ADS1261

ADS1261: ADS1261

Ram Ch
Prodigy 120 points

Part Number: ADS1261

Hi Bryan,

I am using below register configuration for ADS1261 in my application.

MODE0: 1200 SPS, sinc 1

MODE1: Normal mode, CONVERT=Pulse, DELAY=17.8 ms

REF: REFENB=Internal Ref Enabled, RMUXP=Internal Positive, RMUXN=Internal Negative

PGA: PGA Mode, GAIN=1(=000)

INPBIAS: VBIAS Enabled

AVDD and AVSS are connected to 5V and Gnd respectively.

1) with above configuration I tried to measure the voltage between 'Internal (AVDD - AVSS) / 4' positive and 'AINCOM'. i.e., the INPMUX Register value is 0xC0.

         (AVDD - AVSS) / 4 = (5-0) = ~1.25V

         AINCOM =  (AVDD + AVSS) / 2 (when VBIAS enabled)

                        = (5+0)/2 = ~2.5V

        I would expect -1.25V as the ADC count value but I am always getting ~0.625V. 

        Now, I reverted the INPUMUX register configuration i.e., 0x0C. here also I am getting the ADC count value ~0.62V.

        I am always getting positive value and also not the expected value. 

        Could you please tell me the reason behind this?

        Also, I changed the Internal reference to AVDD internal and AVSS internal. repeated the above  experiment. here also I got value as ~0.625V. 

2)  In INPMUX register, what should be selected in Negative Inpux MUX value for single ended measurements? 

Thanks,

Ram.

        

        

  • +1
    TI__Guru 59361 points

    Hi Ram,

    To successfully read back 'Internal (AVDD - AVSS) / 4', you should select the INPMUX channels as per the highlighted image below. In other words, do not select AINCOM as one of the channels. Please try the settings highlighted below and let me know if this results in the correct reading (~1.25 V).

    For single-ended measurements: the ADC always reads differentially between the two selected channels in the INPMUX register. So you would need to connect one of the analog inputs to ground and then select this channel as MUXN in the INPMUX register.

    -Bryan

  • 0
    Prodigy 120 points

    Thanks Bryan. I was able to see the reading as ~1.25V with this configuration.

    -Ram.