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ADS1298 Single-Ended Input Range
Part Number: ADS131E08S
I would like to ask about the single ended input range of the ADS131E08S, if I use a unipolar power supply of Avdd=5V and use the internal Vref=2.4V, and set INN=0 V, what is the allowed voltage range at the INP? can it varry varry between -0.3V and 2.4V? taking in to consideration the limit imposed by the Avdd?
What if I use a bibolar power supplu -2.5 to 2.5 V, and use the internal Vref=4V, set INN=0V, Is the allowed voltage range at the INP varry between -2.8V and 2.1V? taking in to consideration the limit imposed by the Avdd?
Hello Mahlet, Thanks for your post! In the first scenario that you describe AVDD = 5V, AVSS = 0V = INN, Vref = 2.4V. You are correct that it can vary from -0.3V to 2.4V, however I would recommend that you limit the signal to 0 to 2.4V. In the second scenario INP can swing from -2.5V to 2.5V, however since you are using a 4V reference you will not be taking advantage of the full scale range. It makes more sense to use the 4V reference in the first scenario, giving you an INP range of 0 to 4V and 2.4V reference in the second scenario giving you an INP range of -2.4V to 2.4V. This setup will allow you to take advantage of the full scale range of the device. Additionally, all of this is assuming a PGA gain of 1. These input ranges are all divided by the gain since these parameters are the input limits of the ADC.
Alex SmithApplications Engineer | Precision Delta-Sigma Converters
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In reply to Alexander Smith:
Thanks again! What I am wondering is how the input common mode range affects the fullscale that is allowed in the INP pin, because for Vref=4V, AVDD=5V, AVSS=0V ,the CM is given as, 2.7<Vcm<2.3 using the equation below.
Looking at the datasheet page18, it seems that I can not use the INN pin at gnd, for this scenario because for the pseudo diffrential (single ended) mode it should be kept at mid supply, this means 2.5V? Right?
And from the above picture and explanation, what I understood is the InxP can only vary 400mVpp around the common mode voltage =2.5V, this seems extremely small value in my opinion, It would be great to hear your explanation regarding this.
In reply to Mahlet Zewde:
Sorry for that. here is the question with the attachment again.
And from the above picture and explanation, what I understood is the InxP can only vary 400mVpp around the common mode voltage =2.5V, this seems extremely small value in my opinion, It would be great to hear your explanation regarding this. Does this mean INN=2.5V and InP can varry between CM+Vref/2 and CM-Vref/2(0.5V-4.5V)?
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