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ADS1261EVM: First Time ADC User In Need Of Simple Advice

Part Number: ADS1261EVM
Other Parts Discussed in Thread: ADS1261

Hi. I was wandering if someone can give me some quick tips for using the ADS1261EVM. I'm not completely new to the concept of AD converters, but it's my first time actually using one and trying to get it to work.

I have successfully installed the drivers, the support package and the Delta Sigma software and I have the board properly connected to my PC.

I'm now trying to receive a signal and view the data in the software. But I only see static noise and no real values. I have a precision DC powersupply connected to ground to ground and I connected the positive wire to different connectors. I have the slight feeling that I'm doing something fundamentally wrong in how I connect my source.

My questions:

  • Do I have to wire the ground of my supply to the ground on the EVM?
  • Does the software automatically detect which pin is connected and which isn't?
  • Could the problem be that the EVM only measures differentially, and I need a reference signal to compare my supply voltage to`?

I hope my questions aren't to silly and I've provided enough information but I couldn't find a post about how to properly set up the EVM. I've read through both the manuel for the EVM and the software but I couldn't find anything regarding connection a source. In the end I hope to connect something like a shunt or a thermal probe of some kind to build a small explample circuit.

Greetings,

Martin

  • Martin,


    Because you've been able to install the device drivers and Delta Sigma software, and then run the software to take some data, I think you're pretty close to getting some real data. However, let me address some of your questions.

    1. The ground of the supply should connect to the ground of the EVM. Normally the input must have some DC common-mode voltage that is in the input range of the device. The input voltage should not float.Also make sure that the inputs do not go above 5V if you are using 5V for AVDD. Over voltaging the inputs may be destructive to the device. If your power supply is capable of putting out high voltages, or can source significant current, you may want to add some series resistance to reduce the risk of damage to the device and board.

    2. The software does not automatically detect which pin is connected to the ADC. You must manually select which pin is AINP and which pin is AINN. You will be able to select these inputs with the INPMUX bits in the register map. Additionally, you will need a reference for the ADC. I would start by enabling the internal reference and using that for the ADC reference. You can set that up in the REF bits in the register map.

    3. The ADC only makes differential measurements, measuring the value of AINP-AINN. Additionally, the PGA has a limited input range that varies with the gain. Even with PGA=1, the input is limited and neither AINN and AINP can be connected to ground. If you need to make measurements with respect to ground, then you should bypass the PGA, disabling it. This way ground is within the input range of the ADC (as long as gain=1 is fine).

    After you check the above points, take some measurements again. If everything goes correctly, you should be able to verify the input voltage based on the output code and the reference voltage.

    Hopefully this was some help for you. I would definitely consider the input selections for AINP and AINN, and then make sure that the ADC is making a comparison to a reference that is enabled.


    Joseph Wu
  • Hey :) Thanks for the great advice. I knew I had some configuring to do, but wasn't quite sure how. Thanks to you I got it running now with some small quirks I can't quite figure out myself. But thanks so much!

    I've selected AIN0 as my positive input and used the intertal vcom as my negative reference:

    I've then enabled the Internal reference function just as you suggested and kept the rest of the settings at default:

    Now I've managed to get a first measurement. I set my external power voltage supply to 3.5V (Iout,max is rated as 0.8mA) and I got this result:

    The only thing I can't quite rap my head around is the fact that I only get a value somewhat close to my set inputvoltage if I set VRef in the Data Analysis Tab to 5V. If I don't, I simply get a fraction of the estimated value. If I set it to 2.5V I get halfe of what I expect. I'm not quite sure why this is happening, but I think I simply don't understand the concept of the reference yet. I'm gonna do some more digging in the manuals and datasheets.

    Can you maybe elaborate some more on how using different settings for the referencing affects my measurement?

  • Hi Martin,

    I noticed that you're are configuring the ADS1261 to measure the differential voltage between AIN0 and Internal VCOM, and for the reference voltage you are selecting the differential voltage between AVDD and the internal REF N.

    Please note that "Internal VCOM" is connected to a mid-supply voltage (~2.5V). Therefore, the ADC is measuring the differential voltage between AIN0 and 2.5V. This is probably why you are only measuring half of the voltage you are expecting.

    For the reference configuration, I would recommend setting RMUXP and RMUXN to either be connected to the internal 2.5V reference OR the internal ~5V supply reference. Whichever one you select will set the maximum input voltage you can measure (you can never measure a differential input voltage that is greater than VREF / PGA).You must then also tell the GUI if the ADS1261 is connected to the 2.5V or 5V reference so that it can properly scale the voltage correctly on time-domain plot.

    I hope that helps!

    Best regards,
    Chris