Input Common-Mode Range of INA331

Hi Pete,

Thanks for the information.

What wil be the common mode range for INA331 when powered by 5V and ground and the reference pin is tied to ground. Input voltage on the negative input will be 110mV and the positive input will be 100 to 300mV. Gain is approx 22.

According to the datasheet, Input common mode range is 0.55V to 3.8V for Vref = Vs/2.

But in our application we have tied Vref pin to GND as below. Will there be any change in the Vcm..

I will do some analysis and provide you with a response by late tomorrow. 

Attached Powerpoint should answer all of your questions and will provide you with a TINA_TI SPICE model to try your application out in.  The included INA331 DC and Comon Mode model will flag you if you violate any input or output condition of the INA331.  The short answer to your question is that for your condition of Vref=0V, Vcc=5V, Vee=0V, the only allowed input comon mode range is: 0.55V < Vcm < 3.8V.  And remember Vout swing (Vin_differential * gain) is limited as you change Vcm.  Your Application will not work since your Vcm is near 100mV! Use attached to adjust your application Common Mode Input and Vref to make the INA331 work or consider an alternate instrumentation amplifier, such as INA326.  Also in your schematic your R2 and R1 resistors look like they are in the wrong place for a gain of x20.34.

Rev A of powerpoint attached to fix some erros in labeling the models.  No change in technical content.

Rev B powerpoint attached fixes resistor values of 10K and 40k which where swapped on previous posting.  Your main problem remains the same as prevoius posts.  You cannot use INA331 on 5V without moving input common mode to 0.55V to 3.8V range. 

Hi Pete,

Thanks for the information.

I ran the simualtion file and the results are in sync with the explanation provided by you.

I ran the simulation for different input voltages (Common mode voltage) and Reference voltages.The results were not matching with the graph provided in page 5 of INA331 datasheet.

Is this graph is for application where reference voltages > 0V. According to the graph the input common mode range will increase from 0V to 3.8V for Vref = 0V.For Vcm = 550mV, Vdiff = 10mV and Vref = 0V, the simulation results is showing an output voltage of 2.34V which is not matching with the graph shown below.

Graph is for Vdiff = 0V.  Then Vout = Vref for the Input Common Mode range shown.  Use attached revised Model which will show you the linear areas you can operate in without gettign into trouble.  We are workign on new tools and dat sheeet modifications to help make this easier to understand.