INA331: Why the output of INA331 should be less than VDD-1.2V

Hao,

It is NOT the output but rather the reference voltage that must be 1.2V below positive rail:  "The output is referred to the reference terminal, which must be at least 1.2V below the positive supply rail."  This is due to the fact that the input common-mode voltage range extends only 1.2V below positive rail. 

These INA type products have internal node limitations depending upon Input CM voltage, REF voltage, Gain, and differential input voltage.
This link will allow you do download a powerful INA Calculator that can check to see if you are operating your design in a linear region of operation.

www.ti.com/.../ina-cmv-calc

I get it, Thank you

when i simulate the INA331 in TINA, i find that the gain is not 100 but 175， so Do my simulation has some error?

My simulation of TINA just as attachment. 

look forward for your help INA331.TSCThank you.

Thank you

when i simulate the INA331 in TINA, i find that the gain is not 100 but 175， so Do my simulation has some error?

My simulation of TINA just as attachment.

look forward for your help

Thank you.5315.INA331.TSC

i get it, thank you very much