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Re: Welcome to the Iron Circuit Design Contest!
@Matt, I am working with a pressure transducer that outputs 0-30mV and am having some trouble. I have a gain = 65x and when the pressure outputs 15mv x 65 gain = ~1V the INA333 appears to saturate. It will no longer bump up the voltage beyond this 1v (really is ~916mV). The input supply is 3.3V and the pressure sensor is the RTOP100A7 from Sensortechnics (http://www.sensortechnics.com/download/DS_Standard-RTO_E_11714_A.pdf). The INA333 is tied to an MCP3421 ADC. Any help on trouble shooting this would be appreaciated.
The symptoms you are desribing sound suspiciously like an input common mode saturation problem. With higher gain and larger input difference voltages, a lower common mode voltage (i.e. below 1/2 supply) will not allow sufficient swing margin for the output of VOA1 to keep from saturating. My guess is that your common mode voltage is in the range of .5-.7V when this happens. You can fix this by inserting a resistor in between the supplies and ground as shown. This will keep the common mode voltage mid supply which will allow you to use more gain if necessary.
I hope this helps.
Matt, dude you are the man! I was about to throw this design to the "junk pile" and along you came to save the day. I really appreciate your quick response. I was about to start looking at other suppliers but you really sealed the deal here to stay with TI. Please tell management to keep this "beta forum" going, I had a help ticket in and wasn't expecting to hear back at all on this for a few more days.
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