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Original question:

ADS1261: Reference divider, two load cells with the same AC-excitation, single-ended resolution

ADS1261: FS Range and Single Ended Configuration

ismail polat1
Intellectual 255 points
Part Number: ADS1261
Other Parts Discussed in Thread: TIDA-060020

Hi,

What should I do to use single ended 10 channels of ADS1261.

According to related thread, we should use one of the inputs to connection of gnd. Can I use AINCOM pin for gnd connection and other 10 pin for analog input?

I want to use internal reference. If I use single ended configuration, what will be input FS range? (+-2.5V, 0-2.5V or 0-5V)

  • 0
    TI__Mastermind 35241 points

    Hi Ismail,

    Your comments are correct, you can connect any pin to ground and then select the other analog inputs to perform a single-ended measurement. Note that the ADS1261 PGA cannot be enabled for a true single-ended measurement (referenced to ground).

    The ADS1261 has a bipolar input range (-FS to +FS). So if you use the internal reference (2.5V) and a gain of 1, the full-scale range extends from -2.5V to +2.5V (differential). Since you will only be measuring from 0 to 2.5V, you are only using half of the full-scale range. You can always apply 2.5V to one of the analog inputs instead of ground, and then measure your input signal against this fixed 2.5V input. This would be more useful if your input signal is centered around the bias voltage e.g. 0V to 5V.

    -Bryan

  • 0 in reply to Bryan Lizon86
    Intellectual 255 points

    Hi Bryan,

    Thanks for your helpful response. I would like to know why PGA cannot be enabled for single ended signal? I want to make a input module for 4-20mA current loop with this adc and there is an TI evaluation module (TIDA-060020). Current input front-end of this evaluation module has 3 resistors and measurement signal is not referenced to ground. Is reason related with a PGA problem that you mentioned or another thing?

  • 0 in reply to ismail polat1
    TI__Mastermind 35241 points

    Hi Ismail,

    You can reference Equation 5 on page 31 in the ADC datasheet to see why you cannot measure a single-ended signal the ADS1261 PGA enabled (when AVSS = 0V). You would either need to bypass the PGA or use a bipolar supply e.g. AVDD = 2.5V and AVSS = -2.5V

    When you measure a 4-20mA signal using three resistors (assuming you are measuring across the middle resistor), then the measurement is differential, not single-ended. Under these circumstances you could enable the PGA, just make sure you respect the requirements set by Equation 5 in the ADS1261 datasheet.

    -Bryan