RM0440 Rev 4 615/2126
RM0440 Analog-to-digital converters (ADC)
724
The calibration is then initiated by software by setting bit ADCAL=1. Calibration can only be
initiated when the ADC is disabled (when ADEN=0). ADCAL bit stays at 1 during all the
calibration sequence. It is then cleared by hardware as soon the calibration completes. At
this time, the associated calibration factor is stored internally in the analog ADC and also in
the bits CALFACT_S[6:0] or CALFACT_D[6:0] of ADC_CALFACT register (depending on
single-ended or differential input calibration)
The internal analog calibration is kept if the ADC is disabled (ADEN=0). However, if the ADC
is disabled for extended periods, then it is recommended that a new calibration cycle is run
before re-enabling the ADC.
The internal analog calibration is lost each time the power of the ADC is removed (example,
when the product enters in STANDBY or VBAT mode). In this case, to avoid spending time
recalibrating the ADC, it is possible to re-write the calibration factor into the ADC_CALFACT
register without recalibrating, supposing that the software has previously saved the
calibration factor delivered during the previous calibration.
The calibration factor can be written if the ADC is enabled but not converting (ADEN=1 and
ADSTART=0 and JADSTART=0). Then, at the next start of conversion, the calibration factor
will automatically be injected into the analog ADC. This loading is transparent and does not
add any cycle latency to the start of the conversion. It is recommended to recalibrate when
V
REF+
voltage changed more than 10%.
Software procedure to calibrate the ADC
1. Ensure DEEPPWD=0, ADVREGEN=1 and that ADC voltage regulator startup time has
elapsed.
2. Ensure that ADEN=0.
3. Select the input mode for this calibration by setting ADCALDIF=0 (single-ended input)
or ADCALDIF=1 (differential input).
4. Set ADCAL=1.
5. Wait until ADCAL=0.
6. The calibration factor can be read from ADC_CALFACT register.
Figure 89. ADC calibration
t
CAB
ADCAL
ADC State
CALFACT_x[6:0]
0x00 Calibration factor
ADCALDIF
0: Single-ended input 1: Differential input
MSv30263V2
OFF Startup Calibrate OFF
Indicative timings
by S/W by H/W
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