
DocID024597 Rev 5
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RM0351
Operational amplifiers (OPAMP)
699
23
Operational amplifiers (OPAMP)
23.1 Introduction
The device embeds two operational amplifiers with two inputs and one output each. The
three I/Os can be connected to the external pins, this enables any type of external
interconnections. The operational amplifier can be configured internally as a follower or as
an amplifier with a non-inverting gain ranging from 2 to 16.
The positive input can be connected to the internal DAC.
The output can be connected to the internal ADC.
23.2
OPAMP main features
•
Rail-to-rail input and output voltage range
•
Low input bias current (down to 1 nA)
•
Low input offset voltage (1.5 mV after calibration, 3 mV with factory calibration)
•
Low-power mode (current consumption reduced to 30 µA instead of 100 µA)
•
Fast wakeup time (10 µs in normal mode, 30 µs in low-power mode)
•
Gain bandwidth of 1.6 MHz
23.3
OPAMP functional description
The OPAMP has several modes.
Each OPAMP can be individually enabled, when disabled the output is high-impedance.
When enabled, it can be in calibration mode, all input and output of the OPAMP are then
disconnected, or in functional mode.
There are two functional modes, the low-power mode or the normal mode. In functional
mode the inputs and output of the OPAMP are connected as described in the
Section 23.3.3: Signal routing
23.3.1
OPAMP reset and clocks
The operational amplifier clock is necessary for accessing the registers. When the
application does not need to have read or write access to those registers, the clock can be
switched off using the peripheral clock enable register (see OPAMPEN bit in
APB1 peripheral clock enable register 1 (RCC_APB1ENR1)
The bit OPAEN enables and disables the OPAMP operation. The OPAMP registers
configurations should be changed before enabling the OPAEN bit in order to avoid spurious
effects on the output.
When the output of the operational amplifier is no more needed the operational amplifier can
be disabled to save power. All the configurations previously set (including the calibration)
are maintained while OPAMP is disabled.