• Locked Locked
  • Replies 2 replies
  • Subscribers 44 subscribers
  • Views 469 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Re: Welcome to the Iron Circuit Design Contest!

Ryan O'Hara
Prodigy 20 points
Other Parts Discussed in Thread: INA333

@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.

  • TI__Expert 7185 points

    Ryan,

    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

  • in reply to Matthew Hann
    Prodigy 20 points

    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.