Power consumption optimization with STM32F3xx microcontrollers
Contents
1. CTI AN4538 yY rema Application note Power consumption optimization with STM32F3xx microcontrollers Introduction This application note describes how to optimize the power consumption of an application based on STM32F3xx microcontrollers Reducing power consumption while performing complex real time applications presents a major challenge for the recent embedded applications This application note is splitted in two main parts e The first part gives an overview of low power design integrated features and techniques to reduce the power consumption e The second part describes a use case a smart motor control application that highlights the power efficiency of STM32F3xx microcontrollers for the competitive applications of the embedded system market This application note is provided with the STSW STM32036 software package that contains an example of STM32F3xx microcontroller low power application This application is based on the USART DMA timer comparator RTC peripherals using STM32F3xx microcontroller low power modes and features Table 1 Applicable products and software Type Part numbers STM32F301x6 8 STM32F302x6 8 B C D E STM32F303x6 8 B C D E STM32F334xx STM32F373xx STM32F318xx STM32F328xx STM32F358xx STM32F378xx STM32F398xx Software STSW STM32036 Microcontrollers January 2015 DoclD026505 Rev 1 1 25 www st com Contents AN4538 Contents 1 STM32F3xx microcontr2. AN4538 List of tables List of tables Table 1 Applicable products and software 0 0 ce eens 1 Table 2 STM32F3xxxx device power supply considerations 00020 eee ee eaee 7 Table 3 Wake up from low power mode sources 0 cee ee ee eee nee 9 Table 4 Wake up from low power mode timing examples 000002 ee eee eeaee 9 Table 5 low power mode data of the measured example 200000 eee eee eee 22 Table 6 Document revision history 0 0 0 0 00 cece eee 24 d DoclD026505 Rev 1 3 25 List of figures AN4538 List of figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 4 25 Power supply overview in STM32F3xxxx devices with an internal regulator 5 Power supply overview in STM32F3x8xx devices lille 6 Application synoptic lllssssslllllll Ins 12 Application modules and functional interconnections 0 00 eee ees 14 Application state machine liliis eee 15 STM32F3xx microcontroller low power project overview llle leslie 17 NUCLEO F302R8 hardware connection 0 ee eh 20 Log time display of the measured example 0 0000 e cece eee eee 22 3 DocID026505 Rev 1 AN4538 STM32F3xx microcontroller low power overview 1 1 3 STM32F3xx microcontroller low power overview STM32F3xx microcontrollers are based on ARM Cortex M4 core runn
3. RTC wakeup EXTI line 20 to wake up from standby e DAC Channel 1 Data alignment 12 bit data alignment Data 2500 by default it can be modified by the user 3 DoclD026505 Rev 1 AN4538 STM32F3xx microcontroller low power application example 2 3 How to use the application This section describes how to prepare the NUCLEO F302R8 board to be used for the application as well as the steps performed to run correctly the application 2 3 1 Environment setup First read the getting started of the NUCLEO F302R8 board user manual UM1724 to prepare the NUCLEO F302R8 board for a correct use The version of the NUCLEO F302R8 board to be used is MB1136 C 02 with on board 32kHz oscillator The user needs to know about the hardware connections and modifications that must be done before running the application e NUCLEO F302R8 board modifications SB62 and SB63 solder bridges ON Note For more details about LSE please refer to the user manual of STM32 Nucleo board 3 UM1724 e NUCLEO F302R8 board connections Connect the JP5 jumper between pin 2 and pin 3 U5V and make sure the JP1 jumper is off Connect USART2 Tx to USART1 Tx PA2 connected to PAY Connect USART2 Rx to USART1 Rx PA3 connected to PA10 Connect PAO to a button connected to Vpp and GND via pull down Connect the Idd jumper JP6 to the multimeter terminals e NUCLEO F302R8 board connections to the instruments Connect the oscilloscope prob
4. HDMI CEC controller is embedded only in STM32F37xxx devices ADC The STM32F3xxxx devices except for STM32F373 378xx devices embed a low power ADC which consumption is proportional to the speed The lowest consumption is got with the lowest speed This ADC has two clock sources derived from AHB and PLLCLK clocks Consequently the max speed 5MSPS can be reached even with a slow AHB bus frequency In this case ADC auto delayed feature is available in order to avoid ADC overruns DoclD026505 Rev 1 11 25 STM32F3xx microcontroller low power application example AN4538 2 STM32F3xx microcontroller low power application example This section describes a real use case with STM32F3xx microcontrollers and focuses on the power saving techniques used to reduce the consumption of this application 2 1 Application description The application is designed as a smart motor monitor and control with the integration of different low power modes and features It communicates messages to the user about the different application steps and the log time profile 2 1 1 Functional overview The application is designed using the NUCLEO F302R8 board based on a STM32F302x8 device The main features of this application are e The use of multiple peripherals USART DMA Timer COMP DAC RTC e Theuse of multiple low power modes Sleep Stop Standby e The real time log data RTC calendar LSE The following figure gives an overview of the applicatio
5. digital supply Vpp is turned off and the Vgar pin is connected to an external supply voltage The Vpgar pin powers the Backup domain RTC registers RTC backup register and backup SRAM For a further description of these low power mode features and low power technology of STM32F3xxxx devices you can refer to the RM00313 RM0316 RM0364 RM0365 RMO0366 reference manuals and the relevant datasheets available from the STMicroelectronics web site Wake up from low power modes STM32F3xxxx devices integrate many wakeup sources to offer a flexible power management in a low power application development and to simplify the application design Many I O pins allow to use these different wakeup sources Table 3 describes the different wakeup sources and pins that can be available in STM32F3xxxx devices 3 DoclD026505 Rev 1 AN4538 STM32F3xx microcontroller low power overview Table 3 Wake up from low power mode sources Mode name Entry Wakeup sources Wakeup pins WFI Any interrupt Wakeup event Sleep WEE Comparator can wake up from Sleep up to 7 EXTI lines in STM32F303xB C D E STM32F358xx and STM32F398xx Any EXTI line configured in the EXTI All 1 0 registers internal and external lines PDDS LPDS bits T F EXTI lines connected internally to SLEEPDEEP bit Stop t U S ART WFI or WFE Comparator I2C e CEC O PDDS bit i WKUPx pins x 1 2 3 RTC alarm RTC PAO Standby SLEEPDEEP bit
6. domain considerations Voltage regulator ON VppA2 Vpp Vppa 2 2 4V No when DAC and considerations OPAMP are used From 2V to 3 6V From 2V to 3 6V Voltage regulator OFF VDDA 21 8V when ADC is e POR PDR and used PVD features are 1 8V 8 From 1 65V to 3 6V not available Standby mode is not available Note 1 2 d For more details about the power supply you can refer to the reference manuals RM00313 RM0316 RM0364 RM0365 RM0366 and to the relevant datasheets available from the STMicroelectronics web site Power mode features By default after power on or system reset the STM32F3xx microcontrollers are in Run mode This is a fully active mode that consumes much power even when performing minor tasks Highly optimized low power modes are integrated to save power when the CPU does not need to be kept running thus allowing to achieve the best compromise between a low power consumption a short startup time and available wakeup sources in the application design This part describes the different low power modes available in STM32F3xxxx devices and the related features STM32F3xxxx devices feature four main low power modes e Sleep mode Only the CPU clock is stopped The Cortex M4 clock is stopped and the peripherals are kept running The current consumption increases with the clock frequency As in a Run mode the user needs to know the system clock configuration
7. mode In this mode timer 1 generates the PWM signal and the comparator is active to detect in real time when the non inverting input voltage exceeds the chosen reference voltage inverting input In this case the comparator generates an interruption that wakes up the device from Sleep mode and stops PWM generation via the internal signal OCref_clr After that Sleep mode is entered again to send via DMA the data about previous state and the log time of all states if already enabled When the DMA transfer is completed the device enters Standby mode e States Runt When the device is powered on it configures the system clock and the RTC calendar and wakeup sources Standby After power on the device enters Standby mode after the configuration in Run1 is configured and remains in Standby mode until it is woken up wakeup pin or RTC Run2 After waking up from Standby mode configures USART DMA to be ready for transfer and read time Sleep1 Sends a message to the user via DMA about the possible configurations to select Once the transfer is completed the device wakes up from Sleep1 Run3 Configures the USART wakeup source to be used in Stop mode then reads the time Stop Remains in Stop mode until a USART data is received to wake up the device Rund Configures and starts COMP2 TIM1 and DAC if used then reads the time Sleep2 Sends a message to the user via DMA TIM1 generates a PWM si
8. tamper event external reset in NRST pin PC13 3 WEI or WFE IWDG reset PE6 For EXTI lines connected internally to these peripherals refer to EXTI lines mapping section in the reference manuals CEC Available only in STM32F37xxx PE6 works as wakeup pin only in STM32F303 302xB C D E The wakeup time from low power modes contributes a lot in the power optimization and the application flexibility A trade off has to be done between the low power modes consumption and the correspondent wakeup time Table 4 gives examples of wake up from low power mode timing in STM32F3xx microcontrollers Table 4 Wake up from low power mode timing examples Typ Vpp Vppa73 3 V Parameter Condition Unit STM32F302x6 8 STM32F303xB C STM32F373xx Wake up from Sleep 6 cre cycles Regulator in Run 38 36 3 6 mode Wake up from Stop Regulator in low 57 54 54 us power modes Wake up from SI and IWDG OFF 53 1 51 7 42 7 Standby Ky DoclD026505 Rev 1 9 25 STM32F3xx microcontroller low power overview AN4538 1 4 1 4 1 10 25 STM32F3xx microcontroller power saving techniques General techniques This section gives a brief description of the main power saving features that contribute a lot reducing the current consumption and reaching an optimal trade off between the performance processing and the power efficiency System clock configuration Several prescalers are used to configure the AHB fre
9. the log time of different low power modes existing in the application state machine Figure 8 shows the log time displayed for the first time of the application processing Note that the wakeup time of Sleep3 mode is displayed in the second cycle of the state machine DoclD026505 Rev 1 21 25 STM32F3xx microcontroller low power application example AN4538 Note 22 25 Figure 8 Log time display of the measured example Low power mode time profile is gt gt 00 00 00 000 Enter standby mode 00 00 20 015 Wake up from Standby mode 00 00 20 019 Enter to Sleep 1 mode 00 00 20 101 Wake up from Sleep 1 mode 00 00 20 101 Enter to Stop mode 00 00 33 058 Wake up from Stop mode 00 00 33 058 Enter to Sleep 2 mode 00 00 42 394 Wake up from Sleep 2 mode 00 00 42 398 Enter to Sleep 3 mode gt gt 00 00 42 488 Wake up from Sleep 3 mode The time spent in each mode and the corresponding current consumption helps us to calculate an estimated value of the whole application average current consumption The formula of the average current consumption is as follows l average IRuNx TimeRUNx Istandby Timestandby Isleep1 Timesleept Istop Timestop Isleep2 E Timesieep2 Isleep3 E Timesieep3 Total Time Table 5 gives the time and the current consumption in different low power modes of the measured example For Runx modes x 1 2 3 4 5 6 we assume that they are negligible versus low power modes i
10. 1 MSv36618V1 There are four different wakeup sources PAO wake up from Standby mode USART wakeup source wake up from Stop mode Comparator wake up from Sleep mode RTC wake up from Standby mode DoclD026505 Rev 1 d AN4538 STM32F3xx microcontroller low power application example 2 1 3 State machine The state machine provided in Figure 5 describes the application states and transitions Figure 5 Application state machine DMA transfer on going PAO WUKP 1 or RTC WUKP 1 DMA transfer COMP WUKP 0 on going MSv36619V1 d DoclD026505 Rev 1 15 25 STM32F3xx microcontroller low power application example AN4538 16 25 e State machine Initially the device is in Standby mode First the user pushes the user button to wake up the device from standby If the user does not push the button the device will wake up via RTC after a pre defined period 20 s by default Then the device sends data via the virtual comport see Sleep1 state description Once the transfer is completed the CPU enters Stop mode The device remains in Stop mode until the user pushes a keyboard button to transfer a number from 1 to 4 It will simultaneously wake up the device via USART select the desired configuration of the comparator inverting input Vrefint or DAC1 OUT1 and the RTC display yes or no Then the STM32F302x8 device enters Sleep
11. cleo Project folders B d Low Power Application UseCase EWARM and MDK ARM projects Hj EWARM User header files HA Inc User source files H MDK ARM Readme file u Sre main c _ stm32f3xx hal msp c _ stm32f3 x it c 5 readme txt Release Notes html package xml 4 Release Notes html MSv36620V1 DoclD026505 Rev 1 17 25 STM32F3xx microcontroller low power application example AN4538 2 2 2 Note 18 25 Peripherals configuration e Timer1 TIM1 output pin PA8 APB2 Prescaler 1 8 MHz Period 1 20 KHz Pulse 50 of Period OCref clr is enabled to disable the PWM generation when high level is detected e UART1 USART1_Tx PA9 USART1_Rx PA10 Baud Rate 115200 bps Word length 8 bits Stop bits 1 Hardware flow control and parity none UART wakeup from Stop mode EXTI line 25 The virtual comport is connected to the USART2 in the NUCLEO F302R8 board Use USART71 in the software to support the USART wakeup from stop feature USART2 pins should be connected to USAR 1 pins The virtual comport software should be downloaded e COMP2 e RTC COMP2 non inverting input COMP2 INP pin PA7 COMP2 inverting input COMP2 INM VREFINT or DAC1 OUT1 COMP outputs TIM1 OCref clr COMP OUT pin PA12 COMP wakeup from Sleep mode EXTI line 22 Clock source LSE RTC ASYNCH PREDIV Ox7F RTC SYNCH PREDIV 0x00FF RTC OUTPUT disable Calendar format12 hour minute second
12. e to PAG pin Connect the DC power supply output to pin PA7 and regulate it to a voltage lower than the comparator reference voltage 1 2 V if Vrefint selected or 2V if DAC1_OU1 selected Turn off the power supply DoclD026505 Rev 1 19 25 STM32F3xx microcontroller low power application example AN4538 20 25 Figure 7 describes the NUCLEO F302R8 connections that must be set before starting the application Figure 7 NUCLEO F302R8 hardware connection USB cable position U5V PA9 USART1 TX PA8 TIM1 CH1 PA7 COMP2 INE PA10 USART1 RX PA2 USART2 Tj PA3 USART2 RX Oscilloscope DC Power supply MSv36621V1 DoclD026505 Rev 1 d AN4538 STM32F3xx microcontroller low power application example 2 3 2 Note 2 4 2 4 1 d Application setup Once the previous software and hardware recommendations have been followed and the NUCLEO F302R8 is ready to use the user has to proceed as follow e Open a serial port terminal interface in the PC e Connect ST link cable between NUCLEO F302R8 and PC to power on the board e Open the serial port terminal while the device remains in Standby mode e Push the button connected to PAO to start the application state machine or wait for the RTC period to elapse e Once the menu message is displayed select one of the four configuration by pushing the key and send the right character 1 4 see note e Ensure that
13. f 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 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 e USART1 used to send and receive data via virtual comport and to wake up the CPU from Stop mode e DMA used with USART for data transfer from device to PC e Timer 1 used to generate PWM signal e 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 e 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 DoclD026505 Rev 1 13 25 STM32F3xx microcontroller low power application example AN4538 14 25 Figure 4 Application modules and functional interconnections PAO ei Pag e CPU Cortex M4 Wake up from sleep OcrefClear Stop PWM Wake up from standby PA10 e TIMER 1 PWM signal OCC External analog signal e PAS e PA7 Vrefint r 3 DAC1_OUT1 Wake up from standby RTC Calendar Wake up USART
14. gnal The comparator is active to compare the injected analog signal to Vrefint or DAC1_OUT1 When a comparator interruption occurs it wakes up the device from Sleep mode and stops the PWM generation via OCref_clr Run5 Disables TIM1 COMP2 and DAC if used then reads the time prepares to display the log time profile if it is selected Sleep3 Sends a message including the log time profile Once the transfer is completed the device wakes up from Sleep3 mode Run6 Reads the time and saves it in the backup domain Reconfigures the RTC before entering again Standby mode to start a new round d DoclD026505 Rev 1 AN4538 STM32F3xx microcontroller low power application example 2 2 2 2 1 d Software description Architecture description This application uses the STM32F3xx HAL library and contains the following source files Main c contains the needed functions that perform the application state machine e STM32F3xx it c contains the interrupt handlers for the application e STM32F3xx hal msp c contains the needed hardware configuration of the different peripherals used by the application Figure 6 STM32F3xx microcontroller low power project overview AN4538 STM32F3xx Low Power RH _htmresc Drivers folder E i Documentation Drivers BSP subfolder Gy BSP e CMSIS subfolder H STM32F3xx HAL Driver subfolder H i pb H STM32F30 _HAL_Driver Projects E Ju STM32F302R8 Nu
15. her interrupts or events which can wake up the device from both Sleep and Stop modes The outputs can be connected to an I O or to multiple timer inputs in order to trigger control and monitor analog signals during Sleep mode The comparator power consumption versus speed can be adjusted to have the optimum trade off for a given application This feature is available only in the STM32F303 302xB C STM32F358xx STM32F373xx and STM32F378xx devices U S ART All U S ART interfaces can be served by the DMA controller during Sleep mode USART supports a dual clock domain which allows the functionality and wake up from Stop mode USART can wake up from Stop mode via either address match start bit or by RXNE when its clock source is HSI or LSE Such feature facilitates the design and development of the application while maintaining the power efficiency Note that the user can put the IrDA SIR ENDEC in low power mode to save more power 12C DMA can be used to reduce CPU overload and thus the power consumption The 12C is clocked by an independent clock source which allows the I2C to operate independently from the PCLK frequency When the I2C clock source is the HSI the I2C can wake up from Stop mode on address match CEC Consumer Electronics Control protocol can operate at low speeds with a minimum processing and memory overhead It has a clock domain independent from the CPU clock allowing to wake up the MCU from Stop mode on data reception
16. in the application processing reduces the overall average consumption by keeping the device as much as possible in low power modes The best power management approach consists of switching between different power modes taking into account of the application requirements in terms of power consumption wakeup sources time and the peripherals simultaneously Peripherals clock gating The more peripheral blocks active simultaneously the highest the power consumption Substantial power saving can be achieved by gating the clocks of the peripherals that are not in use Using peripheral low power features STM32F3xxxx devices have peripherals with particular power features that allow to design and develop low power applications while maintaining a high flexibility and an easy interaction with the external world For example the devices can wake up from low power modes using USART comparator I2C and CEC 3 DoclD026505 Rev 1 AN4538 STM32F3xx microcontroller low power overview 1 4 2 d Low power features Some STM32F3xxxx peripherals have low power features which facilitate the use of low power modes while maintaining a high processing capability The availability of these features differs between the STM32F3xx microcontrollers COMP The STM32F3xxxx comparators work independently from the PCLK2 clock Thanks to this clock the comparators can even operate in Stop mode Each comparator has its own EXTI line and can generate eit
17. ing up to 72 MHz with a high number of integrated advanced analog peripherals They integrate an efficient power supply architecture and various power modes that lead to the power consumption reduction at the application level and simplify the application design Power supply STM32F3xxxx devices have an optimized power supply architecture to combine real time capabilities digital signal processing and low voltage operations with highly integrated analog peripherals There are two different power supply architectures depending on the availability of the internal voltage regulator in the STM32F3xx microcontrollers STM32F3xxxx device power supply with an internal regulator The embedded voltage regulator is used to supply the internal 1 8 V digital power domain that contains the core the memories and the digital peripherals as described in Figure f Figure 1 Power supply overview in STM32F3xxxx devices with an internal regulator VDDA domain A D converter D A converter VSSA Temp sensor Vppa O Reset block PLL RCs OPAMP Comparators VDD domain 1 8 V domain 1 0 ring vss L Core Standby circuitry Memories VDD Wakeup logic Digital IWDG peripherals Voltage regulator Low voltage detector RTC domain LSE crystal 32K osc BKP registers RCC BDCR register RTC VBAT L MS19668V2 DoclD026505 Rev 1 5 25 STM32F3x
18. n ecosystem Figure 3 Application synoptic NUCLEO BOARD GND Main Menu v COMP2 inverting input Selection Vrefint or DAC1 OUT Log Time display YES NO 2Wake up from Stop mode RXNE a LED light up when COMP2OUT 1 m YEN CEU E TI KE ime Wake up from Log file sleep2 y Log Time Vna ESSEER O RESE v Power modes mb Stop PWM v Wakeup source i v COMP2 status H generation The application starts when the NUCLEO F302R8 is powered on Once the user has pushed the button or the defined RTC time has elapsed the user has to choose the 12 25 DoclD026505 Rev 1 Ly AN4538 STM32F3xx microcontroller low power application example d 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 i
19. n term of processing periods in a such low power application Total time wake up from Sleep3 mode time 42488 ms The current consumption of low power modes is measured by holding the multimeter display in each measured state of the application Table 5 low power mode data of the measured example Execution periods Average measured Low power modes Active peripherals P current consumption ms uA RTC tandb d 2001 4 abu LSE Backup domain 749 3 Sleep1 mode RTC USART1 DMA1 82 2010 Stop mode RTC USART1 12957 24 3 RTC USART1 DMA1 Sleep 2 mode COMP2 TIM1 9336 2080 Sleep3 mode RTC USART1 DMA1 90 2040 Applying the average formula gives average 4 3 20015 2010 82 24 3 12957 2080 9336 2040 90 42488 475 pA So the calculation gives us a good average current consumption compared to the measured one with almost only 1 error 3 DoclD026505 Rev 1 AN4538 Conclusion 3 d Conclusion This application note illustrates the low power features integrated into the STM32F3xx microcontrollers They ensure the best trade off between the power efficiency and high performance This document provides an overview on these power features and describes how to correctly configure the different power modes through a real use case to minimize the power current consumption DoclD026505 Rev 1 23 25 Revision history AN4538 4 24 25 Revision his
20. oller low power overview 5 1 1 Power supply ssssssseseseel eee eee 5 1 1 1 STM32F3xxxx device power supply with an internal regulator 5 1 1 2 STM32F3x8xx device power supply 00020 leslie 6 1 1 3 Power supply summary 000 cee n 6 1 2 Power mode features unuau auaa eee elle 7 1 3 Wake up from low power modes 0000 0c eects 8 1 4 STM32F3xx microcontroller power saving techniques 10 1 4 1 General techniques 000 000 cece eee eee eee 10 1 4 2 Low power features 0000 e eee ees 11 2 STM32F3xx microcontroller low power application example 12 2 1 Application description 0 0 0c eee 12 2 1 1 Functional overview llseeeeeee tees 12 2 1 2 Application modules liliis 13 2 1 3 State machine scole ac egt on eed an Rd 15 2 2 Software description 000 cece ee 17 2 2 1 Architecture description liliis 17 2 2 2 Peripherals configuration 0 0 cee eae 18 2 3 How to use the application llli 19 2 3 1 Environment setup 000 cece eee ees 19 2 3 2 Application setup 0 000 es 21 2 4 Application current consumption 00000 cece eee ees 21 2 4 1 Measuring current consumption 0 0 0 0 cee eee 21 3 CONGIUSION 250606425 5 5k Cote bddsn Ge Sect op esse dec RR E RARE MER 23 4 Revision history rr 24 2 25 DoclD026505 Rev 1 Ky
21. quency the high speed APB APB2 and the low speed APB APB1 domains In Run mode the speed of the system clocks can be reduced by programming the registers prescalers to the highest values in order to provide just the needed clocks to peripherals and avoid the over clocking that causes a consumption penalty The power consumption can be further lowered by gating clocks to the APBx and AHBx peripherals when they are not in use I O configuration To avoid extra I O currents all unused pins should be configured as analog inputs in this mode the schmitt trigger input is disabled providing zero consumption for each I O pin For the output it is recommended to configure the I O speed frequency at the lowest possible speed The user has to avoid the pull up and pull down activation if they are not used and no pull up down configuration is recommended The user has to also disable the MCO pin of the clock output if not used Using direct memory access DMA STM32F3xxxx device peripherals can be accessed through DMA This feature is not just useful to improve the performance it can also be used to reduce the power consumption The CPU must be kept running to avoid overflow on peripherals featuring only one buffer register However with DMA the CPU can go to Sleep mode until the completion of DMA transfer This allows the device to consume less average current over the life of the application Using low power modes Power mode switching
22. rules e Stop mode The lowest power consumption while all the SRAM and registers are kept PLL HSI HSE are disabled All clocks in 1 8 V domain are switched off Voltage regulator is working in normal mode or low power modes Stop mode achieves the lowest power consumption while retaining the content of SRAM and registers All clocks in the 1 8 V domain are stopped the PLL the HSI and the HSE are disabled The voltage regulator can also be put either in normal or in low power modes not available when internal regulator is off DoclD026505 Rev 1 7 25 STM32F3xx microcontroller low power overview AN4538 Note Note 1 3 8 25 e Standby mode The lowest power consumption The 1 8V domain is powered off regulator is disabled SRAM and register contents are lost except in the backup domain The Cortex M4 core is stopped and the clocks are switched off The voltage regulator is disabled and the 1 8 V domain is powered off SRAM and register contents are lost except for the registers in the Backup domain RTC registers RTC backup register and backup SRAM and Standby circuitry Standby mode is not available in devices where the internal regulator is OFF e Vbat mode The main digital supply Vpp is turned off The circuit is supplied through Vgar pin which should be connected to an external supply voltage a battery or any other source This mode is used only when the main
23. the PWM signal is generated and displayed on the oscilloscope e Turn on the DC power supply and apply a DC voltage that exceeds the reference voltage 2 1 2 V if Vrefint is selected or gt 2V if DAC1_OUT71 is selected by modifying the power supply output e Once the message prompting the user that the device will return to standby is displayed execute the sequence again by pushing the button or wait for the RTC period to elapse Depending on the choice done by the user Voltage reference can be 1 2V Vrefint or 2V DAC1 OUT 1 and the log time can be displayed or not in the last message The user has to apply the same sequence of steps described above to get a correct functionality of the application Application current consumption The measure of the application s average current consumption is necessary to estimate the power budget of the application and deduce the battery life for such portable application Measuring current consumption As an example the average current consumption of the first state machine cycle processing has been measured by activating the Min Max mode of the multimeter before powering on the NUCLEO F302R8 board The hold button is pushed just after the first return to Standby mode In this measured case the Vrefint is selected as the inverting input of the comparator 2 and the log time display is activated The average current is equal to 480 pA Before returning to standby the application displays
24. tory Table 6 Document revision history Date 06 Jan 2015 Revision 1 initial release Changes DoclD026505 Rev 1 d AN4538 IMPORTANT NOTICE PLEASE READ CAREFULLY STMicroelectronics NV and its subsidiaries ST reserve the right to make changes corrections enhancements modifications and improvements to ST products and or to this document at any time without notice Purchasers should obtain the latest relevant information on ST products before placing orders ST products are sold pursuant to ST s terms and conditions of sale in place at the time of order acknowledgement Purchasers are solely responsible for the choice selection and use of ST products and ST assumes no liability for application assistance or the design of Purchasers products No license express or implied to any intellectual property right is granted by ST herein Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product ST and the ST logo are trademarks of ST All other product or service names are the property of their respective owners Information in this document supersedes and replaces information previously supplied in any prior versions of this document 2015 STMicroelectronics All rights reserved d DoclD026505 Rev 1 25 25
25. x microcontroller low power overview AN4538 6 25 STM32F3xx microcontrollers with embedded voltage regulator require a 2 0 V 3 6 V operating supply voltage Vpp and a 2 0 V 3 6 V analog supply voltage VppA STM32F3x8xx device power supply These devices do not contain a voltage regulator Vpp directly supplies the regulator output as described in Figure 2 Figure 2 Power supply overview in STM32F3x8xx devices Vppa domain A D converter VovaL D A converter Vssa Temp sensor Reset block PLL Vpp domain 1 8 V domain Vpp E 1 0 ring Core Wakeup logic Memories IWDG Vss H Digital peripherals NPOR CH Backup domain LSE crystal 32K osc BKP registers Vear DH RCC BDCR register RTC MSv34220V1 The STM32F3xx microcontrollers require a 1 8 V 8 operating voltage supply Vpp and 1 65 V 3 6 V analog voltage supply VppA Standby mode is not supported Power supply summary In both power supply architectures the real time clock RTC and the backup registers can be powered from the Vpgar voltage when the main Vpp supply is off Table 2 summarizes the power supply ranges in both architectures and gives supply conditions to be taken into account 3 DoclD026505 Rev 1 AN4538 STM32F3xx microcontroller low power overview Table 2 STM32F3xxxx device power supply considerations Internal regulator status Vpp VppA Power
Download Pdf Manuals
Related Search