DocID024597 Rev 3 595/1693
RM0351 Operational amplifiers (OPAMP)
602
The user is able to switch from ‘factory’ values to ‘user’ trimmed values using the
USERTRIM bit in the OPAMP_CSR register. This bit is reset at startup and so the ‘factory’
value are applied by default to the OPAMP trimming registers.
User is liable to change the trimming values in calibration or in functional mode.
The offset trimming registers are typically configured after the calibration operation is
initialized by setting bit CALON to 1. When CALON = 1 the inputs of the operational
amplifier are disconnected from the functional environment.
• Setting CALSEL to 1 initializes the offset calibration for the P differential pair (low
voltage reference used).
• Resetting CALSEL to 0 initializes the offset calibration for the N differential pair (high
voltage reference used).
When CALON = 1, the bit CALOUT will reflect the influence of the trimming value selected
by CALSEL and OPALPM. When the value of CALOUT switches between two consecutive
trimming values, this means that those two values are the best trimming values. The
CALOUT flag needs up to 1 ms after the trimming value is changed to become steady (see
t
OFFTRIM
max delay specification in the electrical characteristics section of the datasheet).
Note: The closer the trimming value is to the optimum trimming value, the longer it takes to
stabilize (with a maximum stabilization time remaining below 1 ms in any case).
Table 117. Operating modes and calibration
Mode
Control bits Output
OPAEN OPALPM CALON CALSEL V
OUT
CALOUT
flag
Normal operating
mode
1 0 0 X analog 0
Low-power mode 1 1 0 X analog 0
Power down 0 X X X Z 0
Offset cal high for
normal mode
1 0 1 0 analog X
Offset cal low for
normal mode
1 0 1 1 analog X
Offset cal high for
low-power mode
1 1 1 0 analog X
Offset cal low for
low-power mode
1 1 1 1 analog X
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