DocID026505 Rev 1

13/25

AN4538

STM32F3xx microcontroller low-power application example

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reference voltage which will be used by the comparator to control external analog signal

(motor current threshold).

Once the selection is done, the application starts driving the motor by a PWM signal

generated using timer1. Simultaneously, the comparator controls an input analog signal

(motor current). When this signal reaches the selected reference voltage, the generation of

PWM signal is stopped.

The application embeds several power modes that allow optimizing the whole application

power consumption. The RTC timer is enabled during the whole application to save time of

each state. The application communicates messages to the user about the main application

transitions. The log time of different states can be displayed, if this feature has been enabled

by the user. This log time profile gives the opportunity to the user to calculate easily the

application power budget.

2.1.2

Application modules

The application is based on a NUCLEO-F302R8, connected to a PC via USB cable.

The main STM32F302x8 peripherals used by this application are:

•

USART1: used to send and receive data via virtual comport and to wake up the CPU

from Stop mode.

•

DMA: used with USART for data transfer from device to PC

•

Timer 1: used to generate PWM signal.

•

Comparator 2: used to stop PWM generation and wake up the CPU from Sleep mode

when the non inverting input voltage exceeds the reference voltage.

•

RTC: used to run a calendar in the whole application and to wake up the CPU from

standby after the pre-defined time has elapsed.

Figure 4 summarizes the different modules of the application and the relevant functional

interconnections.