Part Number: INA333
I am using the INA333 in-amp in an analogue board to amplify a sensor signal before AD conversion. Below is the schematic of the prototype board and the outline of the copper pathways on the PCB. The names and values of the elements are on the schematic.
The in-amp is powered with -0.231V on the negative power terminal and 3.3V on the positive power terminal. I have checked these multiple times. According to the data sheet, the amp should be able to provide outputs between -0.225V and 3.25V, however what actually happens is presented on the screenshot below (blue is input signal, yellow is output pin of in-amp). The signal can reach the negative rail, but it is capped at 0.45V when driven towards the positive rail. Furthermore, for sufficiently large signals I can see that the output can still be pulled up beyond that sudden “cap”. It is as if the in-amp works in two distinct linear regions: one between -0.23V and 0.45V and one above 0.45V. This is visualized on the oscilloscope screenshots below as I am increasing input signal amplitude.
The RG is 390 ohm, which should provide a gain of 256. The range measured when testing the circuit is similar, and this does not seem to be a problem. Reference is set to ground and I have been driving the in-amps directly from a signal generator. The result was the same whether the signal generator was grounded to the board or not.
I get the same result for all three amplifiers which can be directly connected to the signal generator. Please ignore the part of the circuit that incorporates the multiplexer.
I would greatly appreciate help in solving this issue. Thank you.
