OPA189: OPA189 impedance value issue

Hi Raj,

The OPA189 is an auto-zero op amp that uses active switching in the input signal path to adjust the input voltage offset as close to zero volts as possible. The average input bias current is very low, but there are much higher, short duration current pulses produced due to charge transfer that occurs during switching, and this will result what your observed with the large feedback resistors (result in larger input voltage offset - bias current through the very large resistances for a given voltage gain).

I do not recommend using an auto-zero op amp for this application. Instead, choose a non-autozero or chopper op amp such as the OPA192. It is a CMOS op amp having a more conventional, non-switching design where the input current is very low and relatively constant. Here's a link to the OPA192 datasheet:

https://www.ti.com/lit/ds/symlink/opa192.pdf

Enclosed is a previous resistor matching post for the difference amplifier for your reference. 

https://e2e.ti.com/blogs_/archives/b/thesignal/posts/difference-amplifiers-the-need-for-well-matched-resistors

If you have additional questions, please let us know. 

Best,

Raymond

Hi Raj,

The OPA192 products are in stock. If you are looking for specific package, it may be out of stock current, see the information and link below. OPA192-Q1 is the automotive version of OPA192 part. 

https://www.ti.com/product/OPA192?utm_source=google&utm_medium=cpc&utm_campaign=asc-amps-null-prodfolderdynamic-cpc-pf-google-wwe&utm_content=prodfolddynamic&ds_k=DYNAMIC+SEARCH+ADS&DCM=yes&gclid=Cj0KCQiAnaeNBhCUARIsABEee8Wonn1Xk3gtRQqQYM4eNa3G8kv_nCUVHXpRF9ycmqtk9IcpNr9MuCgaApDUEALw_wcB&gclsrc=aw.ds#order-quality

so please can u suggests the some other IC part no.

You may also try OPA197. If the application does not require >10MHz BW, you may try OPA191 and/or OPA196 (up to 2.5MHz BW). 

If you have additional questions, please let us know. 

Best,

Raymond