Hi Everyone,
we need some help concerning the setup attached as file:
OPA454 is used in a constant current measurement set up for high resistor values > 1MOhm. Without attaching a resistor (Rx) everything is fine. A quiescent current of round about 4mA @100V can be measured for each opamp as stated in the datasheet.
But after inserting a resistor power consumption increases more than I would expect. Normally I would expect a current of more ore less quiescent current plus current flowing through load which is defined by Uri/Ri in our case.
That would mean a max. current of additional 10uA@100V when selecting lowest measuremt range (160k).
But when I take a look at my current meter I can see a current consumption of round about 7mA for each OPA454. That seems to me much too high for that case. With respect to the information in the datasheet I cannot find a good explanaition for this issue.The only one I could think of is that internal power consumption of OPA454 increases by this even when driving very high impedance loads but I cannot belive that this is true.
I also removed ectrenal protection circuits and the additional OPA141 and the analog switch to be sure that this has no influece but nothing changed. So it must have to do with the Opamp and external circuit itself.
Any idea what goes wrong ??
Any help is very appreciated
Thanks, Christian