ST STM32F301 6 Series Reference Manual page 242

Analog-to-digital converters (ADC)
Note: The VBATEN bit must be set to enable the conversion of internal channel ADC1_IN17
(V ).
BATEN
12.3.31 Monitoring the internal voltage reference
It is possible to monitor the internal voltage reference (V
evaluating the ADC V
The internal voltage reference is internally connected to the input channel 18 of the two
ADCs (ADCx_IN18).
Refer to the electrical characteristics section of the STM32F3xx datasheet for the sampling
time value to be applied when converting the internal voltage reference voltage.
Figure 69
Calculating the actual V
The V
DDA
not precisely known. The embedded internal voltage reference (V
data acquired by the ADC during the manufacturing process at V
evaluate the actual V
The following formula gives the actual V
Where:
•
VREFINT_CAL is the VREFINT calibration value
•
VREFINT_DATA is the actual VREFINT output value converted by ADC
Converting a supply-relative ADC measurement to an absolute voltage value
The ADC is designed to deliver a digital value corresponding to the ratio between the analog
power supply and the voltage applied on the converted channel. For most application use
cases, it is necessary to convert this ratio into a voltage independent of V
applications where V
the following formula to get this absolute value:
For applications where V
reference and V
the actual V
formula:
Where:
•
VREFINT_CAL is the VREFINT calibration value
•
ADCx_DATA is the value measured by the ADC on channel x (right-aligned)
•
VREFINT_DATA is the actual VREFINT output value converted by the ADC
•
FULL_SCALE is the maximum digital value of the ADC output. For example with 12-bit
resolution, it will be 2
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voltage level.
REF+
shows the block diagram of the V
DDA
power supply voltage applied to the microcontroller may be subject to variation or
voltage level.
DDA
V
DDA
is known and ADC converted values are right-aligned user can use
DDA
V
CHANNELx
value is not known, user must use the internal voltage
DDA
can be replaced by the expression provided in the section
DDA
voltage using the internal reference
DDA
V
CHANNELx
12
- 1 = 4095 or with 8-bit resolution, 2
sensing feature.
REFINT
voltage using the internal reference voltage
voltage supplying the device:
DDA
= 3.3 V ₓ VREFINT_CAL / VREFINT_DATA
V
DDA
------------------------------------ - ×
=
FULL_SCALE
voltage, resulting in the following
×
3.3 V VREFINT_CAL
= ------------------------------------------------------------------------------------------------------- -
×
VREFINT_DATA
RM0366 Rev 5
) to have a reference point for
REFINT
) and its calibration
REFINT
= 3.3 V can be used to
DDA
DDA
ADCx_DATA
×
ADCx_DATA
FULL_SCALE
8
- 1 = 255.
RM0366
. For
Calculating