ST STM32F301 6 Series Reference Manual page 306

Operational amplifier (OPAMP)
15.3.7 OPAMP modes
The operational amplifier inputs and outputs are all accessible on terminals. The amplifiers
can be used in multiple configuration environments:
•
Standalone mode (external gain setting mode)
•
Follower configuration mode
•
PGA modes
Important note: the amplifier output pin is directly connected to the output pad to minimize
the output impedance. It cannot be used as a general purpose I/O, even if the amplifier is
configured as a PGA and only connected to the ADC channel.
Note: The impedance of the signal must be maintained below a level which avoids the input
leakage to create significant artefacts (due to a resistive drop in the source). Please refer to
the electrical characteristics section in the datasheet for further details.
Standalone mode (external gain setting mode)
The external gain setting mode gives full flexibility to choose the amplifier configuration and
feedback networks. This mode is enabled by writing the VM_SEL bits in the OPAMPx_CR
register to 00 or 01, to connect the inverting inputs to one of the two possible I/Os.
1. This figure gives an example in an inverting configuration. Any other option is possible, including
comparator mode.
Follower configuration mode
The amplifier can be configured as a follower, by setting the VM_SEL bits to 11 in the
OPAMPx_CR register. This allows you for instance to buffer signals with a relatively high
306/874
Figure 83. Standalone mode: external gain setting mode
STM32
VP0
VP1
VP2
VP3
VM0
VM1
RM0366 Rev 5
+ +
OpAmp p p
- -
RM0366
ADC
MS19226V1