Abnormal use of parts LM8261M5/NOPB

Please show an oscilloscope trace of the input and output voltages.

Hi Daniel,

don't let the inputs of unused OPAmps float. Connect the unused OPAmps as voltage followers with the +inputs connected to GND.

Then, OP2B and OP4B should have a resistor from the +input to GND to provide a path for the input bias currents.

Also, mount an isolation resistor at the output of each LM8261. See section 7.2 of datasheet.

By the way, why have you mounted two voltage followers in series? Wouldn't be one OPA140 sufficient?

Kai

Hello Daniel

What is the purpose of the relays?

1. After replacing the abnormal parts, it can be tested normally
2. The boards with other batch numbers are all normal in the client test
Therefore, the circuit problem in this area is ruled out.

Daniel,

Are you are satisfied with the part replacement solution on this board?

I believe your application design depends on OPA140 op amps having a unidirectional IIB current flow such that the output will rail so it won't pickup any signal. The data sheet specification shows possibility of both IIB polarities in the same device. However, I have very little information about the test setup mentioned in the first post.