STM32L151XE datasheet(27/136 Pages) STMICROELECTRONICS

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DS10002 Rev 10

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STM32L151xE STM32L152xE

Functional overview

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:

–

DAC output

–

External I/O

–

Internal reference voltage (VREFINT) or a sub-multiple (1/4, 1/2, 3/4)

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

VREFINT.

3.15

Touch sensing

The STM32L151xE and STM32L152xE devices provide a simple solution for adding

capacitive sensing functionality to any application. Thesedevices 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 interface).

Reliable touch sensing functionality can be quickly and easily implemented using the free

STM32L1xx STMTouch touch sensing firmware library.

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