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ADS1261: ADS1261

Yong Zheng
Prodigy 100 points
Part Number: ADS1261

Hi,

We plan to use ADS1261 in our design.There are 10 analog single-ended signals with voltage range from 0 to 4.5V. We plan to connect them to AIN0 through AIN9. AVDD will be powered at 5V and also used as reference voltage. After reading the datasheet, I come up a few questions and hopefully you can help me clear them up:

1. Should AINCOM be connected to analog ground? Could it be left floating? Does each of analog input have to use AINCOM as its ground reference?

2. Could we use ADS1261 internal PGA with its gain set to 1 or have to bypass it in our case?

3. Since the internal 2.5V reference voltage is not use, could we leave REFOUT pin open without 10uF capacitor?

4. Are there any other things we have to pay attention?

Thank you!

Yong

  • 0
    TI__Mastermind 44680 points

    Hi Yong,

    I'm sorry for the delayed response. I can help you with these questions...

    1. AINCOM is not different for any of the other analog input pins, in that any analog input can be used a common reference for multiple single-ended inputs. However, by convention (and by name) AINCOM is often used for this purpose.

      If AINCOM is not used it can left-floating.


    2. Assuming AVSS = GND = 0V, if the PGA is enabled and set to a gain of 1, then the PGA will not allow for input voltages below 0.3V. When the input voltage is within 0.3V of either AVDD or AVSS the PGA output will be saturated and you'll see an error in the conversion result.

      Therefore, if you need to measure below 0.3V, then the PGA will need to be bypassed, OR you'll have to use different voltages for AVDD and AVSS to satisfy the "Absolute input voltage" recommended operating conditions (see pg 7 of the datasheet).


    3. Yes. The external capacitor is only necessary when using the the internal reference.

      If you do try to enable the internal reference and do not have this capacitor, then the internal reference may become unstable.


    4. The ADS1261 measures everything deferentially (even when measuring single-ended inputs). Therefore, make sure that there is a low-impedance connection between AINCOM (if you use this pin as the negative input) and the ground reference voltage for all of your single-ended signals.

      To avoid saturating the PGA, you may need consider level-shifting your input signals or adjusting the AVDD/AVSS supply voltages. You can use the ADS1261 Design Calculator to check your input voltage conditions and see if they satisfy the ADS1261 input range requirements.

  • 0
    Prodigy 100 points

    Thanks Chris for the help!