STM32G474RE opamps bias

[avbotz]

Hello,

I am thinking of buying an nucleo-g474re for 3-channel DMA sampling from the ADCs. Before I acquire one, I'd like to know if it can fit my use case. There are three analog input sources. Each one ranges from -100mV to +100mV. Is it possible for me to use 3 opamp pins to offset the negative voltages to positive and subsequently amplify to 3.3V? I know it is possible to use the DAC to set the input voltage offset with at least one pin, but I would like to know if this can be done for three. Once I offset, can I route directly to the ADC pins? Can I do this all internally, with no external wires, resistors, and boards?

Thank you for your help

[MasterT]

Configure 3 OPA's as inverting  Gain = -15, non-inverting input's internaly routed to DAC's (have to use 3 of them) pre-set bias is +100mV. Than external signal +100mV translates to output as +100mV, and -100mV to +3100mV.

[TDK]

> Each one ranges from -100mV to +100mV.

No, this isn't possible. The OPAMP can't accept inputs below VSS.

[avbotz]

Hello MasterT,

    Thank you for your response. Would the OPAMP be able to read negative voltages in inverted mode? This is in reference to TDK's comment that the OPAMP can't accept inputs below 0. 

Thanks

[MasterT · Accepted solution]

Yes, inverting mode accepts negative voltage, since input signal is driving resistive matrix and OPA inputs stay at +100 mV.  There is schottky diodes on any inputs of the IC, including digital and analog inputs, but I think all should be fine for about -200mV, if more negative voltage is presents than external R is a cure in series with inverting input. Gain 'd be different, but easy to calculate /recalibrate