OPA392: Temperature drift of OPA392 at high temperatures

Conor

Part Number: OPA392
Other Parts Discussed in Thread: OPA928

Hi,

We are evaluating OPA392, but drift occurs at high temperatures of 120℃. At room temperature, it operates normally and no drift occurs.

The cause is probably a leak between the sensor's input signal line and GND. This can be reproduced by inserting a resistance of less than 1GΩ (gigaohm) between the input signal line and GND in the simulation.

The OPA392 is hand-mounted on the universal board, and the jumper connection is made as short as possible to the input stage of the charge amplifier.
However, there is a limit to the shortest wiring, and I don't know if it is due to the influence of the jumper's inductor or the stray capacitance of the universal board, but we are unable to suppress drift due to leakage. Or it could simply be the temperature characteristics of the input bias current.

Is it possible to get some advice or comments?

Thanks,

Conor

11 months ago

0 Art Kay 11 months ago

TI__Mastermind 22297 points

Conor,

The OPA392 is a good device for low input bias current. However, at high temperature there will be some increase in bias current. The maximum specification for IB is 30pA at 125C. For a 1GΩ input impedance this translates into an offset of 30pA x 1GΩ = 30mV. Is your drift on this order?
The OPA928 is a new device that is in preview, but EVM and samples are available. This device is actually tested at high temperature and has a very low IB at 85C (0.02pA). The advanced information doesn't include a graph for IB to 125C, but based on the 85C specification it should have much better Ib drift over temperature. You should look at this device and see if it may work for your application.
I think in your case the issue is likely related to Ib drift. However, the low IB applications can be very challenging and there are many possible issues that can impact accuracy. Below is a really nice article series on the subject. You should read through the series and see if there is any accuracy consideration you have not looked into.

https://www.edn.com/design-femtoampere-circuits-with-low-leakage-part-one/

https://www.edn.com/design-femtoampere-circuits-with-low-leakage-part-2-component-selection/

https://www.edn.com/design-femtoampere-circuits-with-low-leakage-part-3-low-current-design-techniques/

Best regards,

Art

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OPA392: Temperature drift of OPA392 at high temperatures