Other Parts Discussed in Thread: INA290, TINA-TI, INA190
Dear E2E Staff,
in using the INA118 to measure the current flowing into a sensing resistors, we noticed that the Vos effect on the current read-out does change with Vdiff at the input of the INA. The overall effect is compatible with a Vos which depends from Vdiff. The Vos vs. Vdiff modulation is evident for Vdiff values close to the Vos values published on the data sheet. As a consequence, we concluded that a minimum Vdiff is needed at the input of the INA in order to guarantee linear operations. Such Vdiff(min) seems to be of the order of the Vos(typ) published on the datasheet.
I did not find any comment in the data sheet and/or in specific app notes on such effects. Notably, I have found this comment in the INA290 data sheet:
The linear range of the output stage is limited to how close the output voltage can approach ground under zero-input conditions. The zero current output voltage of the INAx290 is very small, with a maximum of GND + 25 mV.Make sure to apply a sense voltage of (25 mV / Gain) or greater to keep the INAx290 output in the linear region of operation.
I am wondering if something like that does apply to the INA118 and, more in general, to all instrumentation amplifiers. In our application, we have to measure current in the sub-uA range, so such behavior comes into action. It would be very useful to have a plot of Vos vs. Vdiff and/or any plot showing the Vdiff vs. Vout trend for very low Vdiff values, in the range of tens of Vos, where the classic gain equation seems to fail.
Thank you so much for your help and support.
Best,
Alberto