ST STM32L4 5 Series User Manual

Analog-to-digital converters (ADC) RM0351
578/1830 DocID024597 Rev 5
Calculating the actual V
DDA
voltage using the internal reference voltage
The V
DDA
power supply voltage applied to the microcontroller may be subject to variation or
not precisely known. The embedded internal voltage reference (V
REFINT
) and its calibration
data acquired by the ADC during the manufacturing process at V
DDA
= 3.0 V can be used to
evaluate the actual V
DDA
voltage level.
The following formula gives the actual V
DDA
voltage supplying the device:
V
DDA
= 3.0 V x VREFINT_CAL / VREFINT_DATA
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
DDA
. For
applications where V
DDA
is known and ADC converted values are right-aligned you can use
the following formula to get this absolute value:
For applications where V
DDA
value is not known, you must use the internal voltage
reference and V
DDA
can be replaced by the expression provided in Section : Calculating the
actual VDDA voltage using the internal reference voltage, resulting in the following formula:
Where:
• VREFINT_CAL is the VREFINT calibration value
• ADC_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
12
- 1 = 4095 or with 8-bit resolution, 2
8
- 1 = 255.
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.
V
CHANNELx
V
DDA
FULL_SCALE
-------------------------------------
ADCx_DATA×=
V
CHANNELx
3.0 V VREFINT_CAL ADCx_DATA××
VREFINT_DATA FULL_SCALE×
--------------------------------------------------------------------------------------------------------
=

ST STM32L4 5 Series Specifications

General

Brand	ST
Model	STM32L4 5 Series
Category	Microcontrollers
Language	English