Part Number: OPA192
Other Parts Discussed in Thread: TL081H, , OPA191, OPA189, OPA994
Hi,
I have a DC Precision Application (think DVM). In trying to understand a DC Offset problem (possibly oscillation), I've encountered another issue. As an input signal travels through the opamps CMR range, any load on the opamp's output - changes the input to output offset voltage.
Most of the applications are unity gain non-inverting buffers, But I do have a few "inverting" buffers to.
To solve this, I want to use a typical two opamp solution.
OPA192 TL081H COMPOSITE AMP.TSC
The precision front end is the OPA192 and the power "output" stage is a general opamp TL081H. The output opamp is inside the loop. The TI-Tina file is attached.
So, I'm using a composite opamp topology.
I was reading the Ron Mancini (TI) app note "Two Opamps can ruin the stew".
Two op amps can ruin the stew Ron Mancini.pdf
To ensure loop stability, the opamps must have GBWs 5 times different from each other. That is why my TL081H (5MHz) and OPA192 (10MHz) oscillate.
I'm using two opamp types in my design. For general Purpose, the TL081H (extremely low cost). For precision, the OPA189 (For low input impedance) and for high impedance inputs, the OPA191 or OPA192.
I'm prefering SOT-23-5. I have mulitple supply rails of 5V, +/-5V and +/-12V. Its all DC with a loop frequency little greater than 1khz.
What matters very much to me is the DC offset drift versus temperature. I can cancel out DC offset. A few of the functions will have very high imput impedance (100M ohm). Most will drive 1mA to 2mA bipolar loads.
The opamp combination will be used in say 15 locations around the project.
This question must have been asked before and there is probably a TI recomended/preffered solution.
Is there a opamp combination that you can suggest that will work? Or an alternative solution?
Thanks
Peter
