• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 50 subscribers
  • Views 835 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.

OPA2320: Output abnormal when zero input

George Zhao
Intellectual 1635 points

Part Number: OPA2320

Hi team,

The schematic as follows, AD8539 is replaced by OPA2320. The circuit is used to measure current IB+.

The problem is that when zero input, the output can be observed as following picture:

I wonder why the output can look like this? what may causing the periodical spikes?

Thanks and Looking forward to your reply!

George Zhao

  • 0
    Guru 140200 points
    Hi George,

    nice Moiré pattern... :-)

    If TP10 isn't connected to anything, the OPAmp might oscillate. R7=100k is too high for a voltage follower. In combination with the input capacitance of OPAmp a phase lag will be introduced which erodes the phase margin and make the OPAmp oscillate.

    Is TP10 intended to be connected to GND? Which connection is made at TP10?

    Kai
  • 0 in reply to kai klaas69
    TI__Guru 55466 points
    Hi George,

    OPA2 is connected as a difference amplifier with gain=100V/V. The OPA2 circuit is stable with 88 degrees of phase margin (this is assuming TP10 is grounded). The OPA1 (follower) is stable with 79 degrees of phase margin.
    Note, If the input signal IB+ is at zero volts and TP10 is connected to GND, the output of the amplifier should be at the rail; since the output swing of the amplifier is limited to approximately ~10mV-~20mV from GND.

    -What is the input voltage range expected on IB+? and what voltage is TP10 connected to?
    -Can you verify the input voltage at IB+ with oscilloscope when the issue occurs?
    -What voltage is driving the OPA1 (buffer input AAD4) when the issue occurs?

    Thank you and Regards,
    Luis
  • 0 in reply to Luis Chioye
    TI__Genius 11135 points
    George

    We have not heard back from you so we will close this thread. Please reply if further discussion is needed.

    Thanks
    Dennis