Datasheet

DocID022265 Rev 6 19/121
STM32F051x4 STM32F051x6 STM32F051x8 Functional overview
26
3.10.3 V
BAT
battery voltage monitoring
This embedded hardware feature allows the application to measure the V
BAT
battery voltage
using the internal ADC channel ADC_IN18. As the V
BAT
voltage may be higher than V
DDA
,
and thus outside the ADC input range, the V
BAT
pin is internally connected to a bridge
divider by 2. As a consequence, the converted digital value is half the V
BAT
voltage.
3.11 Digital-to-analog converter (DAC)
The 12-bit buffered DAC channels can be used to convert digital signals into analog voltage
signal outputs. The chosen design structure is composed of integrated resistor strings and
an amplifier in non-inverting configuration.
This digital Interface supports the following features:
• Le
ft or right data alignment in 12-bit mode
• Synchronized update capability
• DMA capability
• External triggers for conversion
Five DAC trigger inputs are used in the device. The DAC is triggered through the timer
trig
ger outputs and the DAC interface is generating its own DMA requests.
3.12 Comparators (COMP)
The device embeds two fast rail-to-rail low-power comparators with programmable
reference voltage (internal or external), hysteresis and speed (low speed for low power) and
with selectable output polarity.
The reference voltage can be one of the following:
• Ex
ternal I/O
• DAC output pins
• Internal reference voltage or submultiple (1/4, 1/2, 3/4).Refer to Table 24: Embedded
internal reference voltage for the value and precision of the internal reference voltage.
Both comparators can wake up from STOP mode, generate interrupts and breaks for the
tim
ers and can be also combined into a window comparator.
3.13 Touch sensing controller (TSC)
The STM32F051xx devices provide a simple solution for adding capacitive sensing
functionality to any application. These devices offer up to 18 capacitive sensing channels
distributed over 6 analog I/O groups.
Capacitive sensing technology is able to detect
the presence of a finger near a sensor which
is protected from direct touch by a dielectric (glass, plastic...). The capacitive variation
introduced by the finger (or any conductive object) is measured using a proven
implementation based on a surface charge transfer acquisition principle. It consists in
charging the sensor capacitance and then transferring a part of the accumulated charges
into a sampling capacitor until the voltage across this capacitor has reached a specific
threshold. To limit the CPU bandwidth usage, this acquisition is directly managed by the
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