OPA3S2859: Max gain resistor value

Hi Kuwahara,

Considering OPA3S2859 is built on top of a high-speed op-amp (presumably OPA859), you can use higher gain resistors like 1MΩ. However do keep in mind with higher gain resistors, there will be tradeoffs such as slower settling time, lower slew rate and prone to noise and output voltage offsets (due to resistor rating and input bias, which is minimal in this case, 50pA * 1M = 50uV). 

Regards,
Adam Zahanuddin

Hi Kuwahara-san, 

I have attached a similar query below, where difference between the 3 channels is explained in detail.

https://e2e.ti.com/support/amplifiers-group/amplifiers-internal/f/amplifiers-internal-forum/1429305/opa3s2859-fiberhome-feedback-resistor-for-opa3s2859

For the max Rf limit, I think Adam has explained it very well. If you want to check the effect of Rf (or any other input parameter) on output parameters like: settling time, noise, offset error, etc. The value of Rf resistor also decides the stability of the OpAmp, as Rf and inverting input capacitance of the OpAmp will form a pole in feedback loop. Higher the value of Rf, the OpAmp is closer to instability.

Please have a look at our TIA tool as well as current sensing tool: Analog circuit design studio where you can insert all the input parameters as per your need and check the output parameters accordingly.

Please try out the tool and let me know what do you think.

Another query regarding the same question of difference between 3 channels: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1219902/opa3s2859-ep-opa3s2859-ep-clarification-for-datasheet-specs

Regards,
Aditya