Hi Xiang,
Thank you for your post, I can help you. It is recommended to connect REF to mid-supply because it will increase your output dynamic.
However, we have a calculator tool where you can enter your supplies, gain, reference and common mode voltage (VCM), and the calculator will let you know if you are operating linearly. For example, I chose the INA129, 10V single supply, 1V/V gain, 0 reference, and 5V VCM. The allowable differential voltage range is 0.8V to 55V to yield an output voltage of 0.8V to 6.55V:
You can download the calculator here: https://www.ti.com/tool/ANALOG-ENGINEER-CALC
Click on Amplifiers & Comparators -> and then click on INA VCM v VOUT:
Thank you
I have tried to use the tool, but I not succeed in entering the parameters. The Device name seems not be able to be selected. It always prompts the above message.
Your results seems that it is ok if Ref connects the GND. （the VCM is 5V)
Why the average of the 2 white lines is slightly above the green line? I think 2 white lines and the green line should have the same cross point.
"No rail to rail" here means that the inputs and outputs of the three internal OPAmps go unevenly into saturation when approaching the supply rails:
Which would look for an ideal OPAmp like this:
Kai
Thank you.
Does the following figure means I should tie REF to 5V (1/2 of the supply power) or increase the gain so that the output is obviously larger than 0.8V? The output relative to V- (GND in this application) is 0.8V minimal? Is the following table the evidence?
Does the following figure mean the VIN- and VIN+ should not aproaching V+ and V-. Does the allowed range is listed in the following table? In the following table, the common does not mean (VIN- + VIN+)/2, but rather VIN- and VIN+, doesn't it?
In the tool I can not select device. It is grey. Is the VCM in the page the REF voltage?
However, if I choose another tab. It is ok to select device.
Hi Xiang,
Does the following figure means I should tie REF to 5V (1/2 of the supply power) or increase the gain so that the output is obviously larger than 0.8V? The output relative to V- (GND in this application) is 0.8V minimal? Is the following table the evidence?
Yes. But you don't need to connect midd-supply to the REF pin. Another suited potential could also do.
Does the following figure mean the VIN- and VIN+ should not aproaching V+ and V-. Does the allowed range is listed in the following table? In the following table, the common does not mean (VIN- + VIN+)/2, but rather VIN- and VIN+, doesn't it?
Yes.
In the tool I can not select device. It is grey.
It works for me:
Kai
