Internal OpAmp and ADC sample time

v_ · ‎2013-08-08

Posted on August 08, 2013 at 12:28

I need to adjust the STM32F303 ADC sample time to fit to the internal OpAmp. I can't find any specification of the OpAmps output impedance to take it in account as R AIN for the sampling time table #66 in the data sheet of the MCU.

My only guess would be to take the max. output current of 600 µA assuming that this current will flow at a max. V out = V ref (in my case 3 V) and thus indicating an impedance of 5 kOhm (which would be pretty high for an OpAmp output and as an ADC input source).

Does anyone know the typical value? Is there any STM recommendation for the sample time when using the internal OpAmp-ADC path?

John F. · ‎2013-08-09

Posted on August 09, 2013 at 09:27

No one has replied so here are my thoughts. Use the longest sampling time your system can tolerate. Alternatively, apply a known voltage via the OpAmp and test the accuracy of the measurement at various sample times. This will give you an experimental guide to acceptable times although process and other variations will add uncertainty. You have probably already thought of these. I also looked over the Reference Manual and Application Notes for the part and could not find any useful information about this.

ST should be able to comment. Perhaps this will encourage them to help.