Hi,
I'm getting error result with single power supply.
Vin+ : 2.1V
Vin- : 2.0V
Gain: 9
Vout observed: 1.5V
Vout expected: 0.9V
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Hi,
I'm getting error result with single power supply.
Vin+ : 2.1V
Vin- : 2.0V
Gain: 9
Vout observed: 1.5V
Vout expected: 0.9V
Hi Sadashiva,
I can help you. It looks like we are actually running into input common mode voltage limitations. As you have it now, the input differential voltage (Vd) is 100mV and the common mode input voltage (VCM) is 2.05V. The VCM range on the INA849 is 2.5V from either supply. The second stage difference amplifier also has VCM limitations. We've created a calculator tool that allows a designer to quickly analyze these inputs / outputs.
The calculator tool is called Analog Engineer's Calculator. Please download this and click on "Amplifier and Comparators" and then click on "INA VCM v VOUT". From here, select INA849 from the drop-down menu and click "OK".
Enter the supplies, gain, reference voltage, and common mode voltage, and then click "OK". I created the following plot for you, but I changed the input common mode voltage from 2.05V to 5.45V. You can see from the image below that the allowable input differential voltage range is 22mV to 1.03V, to yield a linear output of 0.2V to 9.3V.
Here is your new circuit with the VCM change.
Thanks for prompt response and technical details. Analog calculator tool is useful and I was not aware of this tool earlier.
I somehow missed to look at common mode voltage associated with INA849.
I tried to simulate with the following spec.
Vin+ : 3.5V
Vin- : 3.4V
Gain: 9
Vdiff: 100mV
VCM: 3.45V
Getting output voltage 1V. Any clue?