Ultra-Low-Power Comparators And Reference Voltage; System Configuration Controller And Routing Interface; Touch Sensing - STMicroelectronics STM32L151RE Manual

STM32L151xE STM32L152xE
3.13

Ultra-low-power comparators and reference voltage

The STM32L151xE and STM32L152xE devices embed two comparators sharing the same
current bias and reference voltage. The reference voltage can be internal or external
(coming from an I/O).
•
One comparator with fixed threshold
•
One comparator with rail-to-rail inputs, fast or slow mode. The threshold can be one of
the following:
–
–
–
Both comparators can wake up from Stop mode, and be combined into a window
comparator.
The internal reference voltage is available externally via a low-power / low-current output
buffer (driving current capability of 1 µA typical).
3.14

System configuration controller and routing interface

The system configuration controller provides the capability to remap some alternate
functions on different I/O ports.
The highly flexible routing interface allows the application firmware to control the routing of
different I/Os to the TIM2, TIM3 and TIM4 timer input captures. It also controls the routing of
internal analog signals to ADC1, COMP1 and COMP2 and the internal reference voltage
V .
REFINT
3.15

Touch sensing

The STM32L151xE and STM32L152xE devices provide a simple solution for adding
capacitive sensing functionality to any application. These devices offer up to 34 capacitive
sensing channels distributed over 11 analog I/O groups. Both software and timer capacitive
sensing acquisition modes are supported.
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 of
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. The capacitive sensing acquisition only requires few external components to
operate. This acquisition is managed directly by the GPIOs, timers and analog I/O groups
(see Section 3.14: System configuration controller and routing
Reliable touch sensing functionality can be quickly and easily implemented using the free
STM32L1xx STMTouch touch sensing firmware library.
DAC output
External I/O
Internal reference voltage (V
DocID025433 Rev 8
) or a sub-multiple (1/4, 1/2, 3/4)
REFINT
Functional overview
interface).
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