Все сказано в datasheet. В RM тоже должно упоминаться. Если корпуса малоногие, в качестве Vref используется Vdda.

всё сказанно в гугле/RM/PM/даташите..... ожидаемый ответ. Я просил ткните носом в даташит, номер страницы, глава.... где это сказано? Я не нашел.

Я же нашел когда-то. И вы найдете.

ADC (analog-to-digital converter)
A 12-bit analog-to-digital converters is embedded into STM32L100C6 and
STM32L100R8/RB devices with up to 20 external channels, performing conversions in
single-shot or scan mode. In scan mode, automatic conversion is performed on a selected
group of analog inputs.
The ADC can be served by the DMA controller.
An analog watchdog feature allows very precise monitoring of the converted voltage of one,
some or all selected channels. An interrupt is generated when the converted voltage is
outside the programmed thresholds.
The events generated by the general-purpose timers (TIMx) can be internally connected to
the ADC start trigger and injection trigger, to allow the application to synchronize A/D
conversions and timers. An injection mode allows high priority conversions to be done by
interrupting a scan mode which runs in as a background task.
The ADC includes a specific low-power mode. The converter is able to operate at maximum
speed even if the CPU is operating at a very low frequency and has an auto-shutdown
function. The ADC’s runtime and analog front-end current consumption are thus minimized
whatever the MCU operating mode.

Поиск Vref по pdf файлам запускали?

Процессор STM32L100RBT6TR. Ткните носом в даташит/RM - где сказано о Vref? Как выбирается источник Vref?

Куча примеров в инете.... разжёвано, как заюзать АЦП... но все примеры заканчиваются считыванием кода АЦП.... результат преобразования равен 0x0123. И что? Сколько вольт на ноге?
Опытным путём на живой плате выяснил, что Vref = 3,3. Ткните носом в документацию, где это сказано?

4.1.1 Independent A/D and D/A converter supply and reference voltage
To improve conversion accuracy, the ADC and the DAC have an independent power supply
which can be separately filtered and shielded from noise on the PCB.
● The ADC and DAC voltage supply input is available on a separate VDDA pin.
● An isolated supply ground connection is provided on pin VSSA.
When available (according to package), VREF- must be tied to VSSA.
On 100-pin packages
To ensure a better accuracy on low-voltage inputs and outputs, the user can connect a
separate external reference voltage on VREF+. VREF+ is the highest voltage, represented by
the full scale value, for an analog input (ADC) or output (DAC) signal. The voltage on VREF+
can range from 2.4 V to VDDA.
On 64-pin packages and packages with less pins
The VREF+ and VREF- pins are not available, they are internally connected to the ADC
voltage supply (VDDA) and ground (VSSA).

Написано в Reference manual RM0041 (не в Data Sheet).