ADS1220: Using ADS1220 in single ended mode - Proper connections

Ahmet,

Below are my answers to your questions in green.  

1. As my voltages are beyond 2.048V internal reference, I have to use external 5V reference. Is this true or although the reference is 2.048 I can measure for example 4.5V?
   1. Using an external reference will allow you to measure voltages up to the reference voltage (gain = 1, PGA bypassed). Assuming you are using a 5V reference, you will be able to read 0V to 5V with a single ended configuration.  You may consider getting the EVM to verify all of your different system requirements.
2. My inputs are connected to AIN0 and AIN2. Is it better to connect AIN1 and AIN3 to GND, and make differential measurements between AIN0&AIN1 and AIN2&AIN3 than single ended measurement? Which one can give better performance in general, single ended or differential?
   1. Differential can be useful if the negative input is at a non-zero voltage.  For example, if your system GND connections has a voltage gradient across it then a differential reading can measure the “GND” at the measurement point and correct for any non-zero GND signal.  If you are confidant that you have minimal voltage difference in you GND plane than connecting AVSS to AINn will allow you to measure more channels.  Please look at figure 38 to understand how AVSS is connected to AINn.
3. Datasheet states that single ended measurements can be made by connecting AINN to AVSS externally or by connecting them to AVSS through software (through MUX). AINN are AIN3 and AIN1 (?), Then actually in total, I can measure two analog voltages in single ended mode, right (because the others are connected to AVSS and cannot be used)?
   1. You can measure all the channels (AIN0, AIN1, AIN2, AIN3) in single ended configuration with respect to AVSS using the internal connection. Please look at figure 38 to understand how AVSS is connected to AINn.

I hope this helps clarify things. 

Best regards,

Art