STMicroelectronics RM0365 Reference Manual page 354

RM0365
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 VDDA voltage using the internal reference
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
Note: If ADC measurements are done using an output format other than 12 bit right-aligned, all the
parameters must first be converted to a compatible format before the calculation is done.
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
V
CHANNELx
12
- 1 = 4095 or with 8-bit resolution, 2
DocID025202 Rev 7
voltage using the internal reference voltage
voltage supplying the device:
DDA
= 3.3 V ₓ VREFINT_CAL / VREFINT_DATA
V
DDA
×
= ------------------------------------ -
FULL_SCALE
×
3.3 V VREFINT_CAL
= ------------------------------------------------------------------------------------------------------- -
×
VREFINT_DATA
Analog-to-digital converters (ADC)
) and its calibration
REFINT
= 3.3 V can be used to
DDA
DDA
ADCx_DATA
voltage, resulting in the following
×
ADCx_DATA
FULL_SCALE
8
- 1 = 255.
. For
Calculating
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