Introducing the low-power concept in automotive applications using
Contents
1. 3V3 IDD v Eal Gain 50 i R s Nm S ce 1000R s T amid VDD Q14 Q13 BG IDD Meas Counter Kr STMBAL3L68T Td PE6 K2 EN4 PC4 LP WakeUp GND MS30843V1 4 16 Doc ID 023129 Rev 1 ky AN4102 Application description 1 5 1 5 1 The resistor is placed in parallel to a high sense operational amplifier A with fixed gain that amplifies the voltage V present on the resistors A sample and hold stage is then inserted and connected to an analog input of the MCU PFO Ipp measurement that finally converts the resulting voltage which reflects the consumption current In low power modes only a counter enabled by the STM8AL PC4 pin manages the measurement timing while the microcontroller is idle The microcontroller is woken up after a 150 ms delay through the K2 switch While the microcontroller is in one of the power saving modes a capacitor C is able to store the measurement charge so that the microcontroller can later give the value of the low power mode current consumption during the microcontroller s wake up phase in the first 50 ms Switch S is opened at the device start up so as to keep the charge collected in the capacitor C intact while the microcontroller is in low power mode The current measurement precision is enhanced by taking into account the bias curren2. LEDs User buttons 12345 4 digit 4 bar LCD display Doc ID 023129 Rev 1 3 16 Application description AN4102 1 4 Application principles 1 4 1 Overview The STM8AL board embeds specific analog and logic hardware connected to the STMS8AL3L68T microcontroller which allows measuring and displaying the IDD current supply when the device is placed in different power consumption modes such as e Run mode e Halt mode e LPR low power run mode with LCD display OFF To see how much power the device is using the user simply needs to read the value displayed on the STM8AL board s LCD panel The units of measurement are displayed accordingly With this demonstration software you can obtain a precise and dynamic measurement of the STMB8AL3L68T s supply current depending on the power mode used 1 4 2 lbp measurement The STM8AL board IDD measurement circuitry consists in measuring precisely the voltage value V at the terminals of a high precision serial resistor 1 inserted between the 43 3 V power supply and the VDD pin of the MCU Depending on the device s power mode the application uses R or 1000 1 x R as the equivalent resistor value by closing or opening K1 In Run mode the current is in the range of mA K1 is closed and the equivalent resistor is R In low power modes the current is in the range of pA K1 is opened and the equivalent resistor is 1001 x R Figure 2 pp measurement equivalent circuitry
3. www st com Contents AN4102 Contents 1 Application description 0 00 cece eee 3 1 1 Hardware required 2 45 33 9 paga d arai spades ne Ia RR ERO AIRE 3 1 2 Hardware settings of the STM8AL board 00 eee eee 3 1 3 Application schematics 0 02 cee ee 3 1 4 Application principles isweesa beet oswe sees ved sekeu Sel Hotes Rares 4 1 4 1 eU AM EET 4 1 4 2 Ipp measurement lsslelseeeseeee ne 4 1 5 Getting started with the application lille 5 1 5 1 IDD measurement ssslleeeseee re 5 1 5 2 Bias current record 0 0000 cece ees 6 1 6 Low power modes cswesx kk ERE REA ey DRO EEWEO HSK ORO L ER Owe aS 7 1 6 1 Low power run mode without LCD 0 0 0 eee eee eee 7 1 6 2 Halt mode csatira ia es dead dw eden beanie ce gai aE ao i keen 9 2 Software description 000 c cece eee eee 10 2 1 STMBAL peripherals used by the application 0 10 2 1 1 ADG 465 ed lei EDT 10 2 1 2 lure Pcr 10 2 1 3 GPI OS xeu E ac eee RE eR eee EG Rm ee Ca RR enda 10 2 1 4 LED controller ur e Rc dh eerie ak dda dox RR ae 10 2 1 5 COCR pierrier Rea e x eu Rc LH E Pree dto Ra 11 2 2 STMa8Lx standard firmware library configuration 11 3 Managing power consumption in automotive applications 12 3 1 Low power application description lllelselreessse 12 4 Conclusion zs iine a q8 EGRE RC RR RR I UL
4. yy AN4102 Application note Introducing the low power concept in automotive applications using the STM8AL board of the STM8A DISCOVERY Introduction This application note illustrates the power consumption benefits of the STM8AL devices included with the STM8A DISCOVERY This new family of devices has been designed to comply with AEC Q100 rev G automotive requirements and offer high performance with ultra low power management capabilities The STMB8AL board of the STM8A DISCOVERY has a built in Ipp measurement feature that is used to demonstrate the efficiency of the low power modes of the STM8AL devices This application does not require any additional hardware or software Once the STM8AL board is powered up through a USB cable connected to the host PC with the USER1 button pressed the user can access the low power software resources of the standard demonstration package This low power software example comes preloaded with your STM8A DISCOVERY but is accessible when the USER1 or USER2 buttons are pressed during the board s power supply sequence Reference documents e STM8A DISCOVERY user manual UM1574 e Application note Power management in STM8L and STM8AL AN3147 The above documents are available from http www st com Table 1 Applicalble products Microcontrollers Type STM8ALxxx Part numbers Evaluation tools STM8A DISCOVERY December 2012 Doc ID 023129 Rev 1 1 16
5. I avg 250 x 10 5s 10 x 10 3s 4 7 x 10 5s Finally the average Ipp current is avg 99 uA If the microcontroller were to be always active the current consumption would be constant and equal to 4 mA The example above shows that the average current consumption is 40 times lower 4 mA vs 100 pA in this operating mode and yet the microcontroller is active approximately a hundred times per second which may be sufficient depending on the considered application The microcontroller s time activity represents about 25 ms over a 1 second operating time 2 596 If the microcontroller needs more activity time then the active idle ratio can be adapted Similarly increasing the clock speed when possible is a key factor to shorten the time spent in the active mode and then decrease the global power consumption of the system On the other hand when there is no activity required until one event happens as for instance a switch that has to be operated before the application performs a series of actions then the MCU can be placed in low power mode until an external event is detected external interrupt peripheral interrupts etc This mode is ideal in terms of energy saving but may not be convenient in the case where high security is required for example when the system needs to regularly control that the microcontroller is present and able to perform any action at any time STM8AL automotive low power microcontrollers allow various con
6. 6 Low power modes for clock management information during low power sequences 2 2 STM8Lx standard firmware library configuration There are no particular settings for the stm8 15x_conf h configuration file All peripheral functions are enabled by default ky Doc ID 023129 Rev 1 11 16 Managing power consumption in automotive applications AN4102 3 3 1 Figure 7 Io lActive lavg lidle Wu tidie Managing power consumption in automotive applications Low power application description The idea behind the low power concept is that the application may be active for a small percentage of the time to perform some of its dedicated tasks but can be placed into an idle mode for a remaining period when activity from the MCU is not required This is especially important at a time where in the electronics world energy saving is becoming more and more important For example 8 bit microcontrollers in the automotive domain are sometimes dedicated to a single task and do not need to be active 100 of the time to perform their operation wiper systems rain sensors door mechatronics etc The idea is to be able to switch the microcontroller into a low power mode for the maximum time to save energy Figure 7 shows a graphical representation of a low power application over time The activity of the MCU can be broken down into three phases e MCU active is the time during which tasks from the microcontroller are pe
7. GPIO Doc ID 023129 Rev 1 7 6 Application description AN4102 Figure 5 Low power run without LCD START Low power mode Executed from RAM LCD disable RTC clock source none rc RTC clock OFF ee LCD clock OFF LSI disable Regulator ultra low power mode GPIO low power config Disable external counter U7 E Switch ON LSI Switch OFF HSI Enable interrupts y Switch OFF Flash memory Switch OFF regulator WFE set to external interrupt from PEG Enable external counter U7 i Wait for event instruction Includes in LPR Init function and RAM segment Interrupt occurred Clear interrupt Disable WFE Switch ON regulator y Switch ON HSI MS30846V1 The parts shown in light green shading are executed from the RAM so that the Flash memory and regulator can be switched off and thus save more power since the LSI oscillator is also switched to act as the main clock source q 8 16 Doc ID 023129 Rev 1 AN4102 Application description 1 6 2 4 Halt mode In this mode the CPU oscillator and peripherals are stopped but the device remains powered on The voltage regulator is configured in ultra low power mode The device wakeup is done via an external interrupt In Halt mode the device reaches a deeper level of energy saving by disabling the oscillat
8. USER push button and the LEDs e PE1 and PE2 are set as input floating pins with interrupt USER push button e PC7andPE7 are set as output push pull pins LD4 and LD3 LEDs respectively e PE6issetasan input floating pin with interrupt IDD wakeup with detection on the rising edge e During the low power modes the I Os are placed in an output push pull configuration to reduce power consumption except for a few pins related to the hardware interface buttons PFO Ipp measurement pin PE6 LP wakeup pin and PC4 e All Schmitt triggers on standard I O pins are disabled to reduce power consumption e TheSchmitt trigger on PFO is disabled so as to avoid measurement errors LCD controller The various functions available in the firmware library for the LCD are used to initialize clear and display strings and scrolling messages needed in the application code For some low power mode measurements the LCD controller is turned OFF to minimize the current consumption of the microcontroller Doc ID 023129 Rev 1 ky AN4102 Software description 2 1 5 Clock The high speed internal HSI 16 MHz oscillator is selected as clock source for the low power demonstration software The application manages the peripheral clocks depending on the selected power saving mode When the device enters low power run mode the HSI is switched OFF and the LSI acts as the main clock source until the device is woken up by an external event See Section 1
9. ada an acl RR ORA d D DU 14 5 Revision history irsisasuuuwa uasa zara dad dn en EORR na ee 15 2 16 Doc ID 023129 Rev 1 ky AN4102 Application description 1 1 Note 1 2 Note 1 3 Application description Hardware required This application uses STM8AL on board LEDs red LD3 and green LD4 a 4 digit 4 bar LCD glass display and two USER push buttons USER1 and USER2 No additional components are required The low power demonstration software can be executed with the STM8AF board either connected or disconnected included with the STM8A Discovery Once the low power demonstration is completed the application automatically launches the LIN communication demonstration software included in the same initial software package An STM8AF board must be connected for correct operation of the LIN communication software otherwise a communication error is displayed Hardware settings of the STM8AL board The IDD jumper JP1 must be placed in the ON position for standard operation except for bias current record operation See Section 1 5 2 Bias current record Solder bridges SB6 to SB8 must be shorted bottom side of the STM8AL board This enables the IDD measurement circuitry hardware Application schematics Figure 1 shows the electrical schematics used in the low power demonstration section Figure 1 Application schematics IDD measurement circuitry E E
10. this mode is launched the different steps automatically unfold as described in the diagram below If one of the measurements is outside the range of the specification the sequence ends with an error message related to the failing measurement Doc ID 023129 Rev 1 5 16 Application description AN4102 1 5 2 6 16 Figure 3 pp measurement sequence description STM8AL board is not powered yet START Press USER1 and and JP2 set to ON position maintain it pressed Y Power supply STM8AL Board LD4 ON Y Release USER1 button ES GM TEST displayed on LCD y LD4 OFF TEST OK displayed on LCD LD4 set Switch to LIN Demo For every step in blue color if the measurement is out the specification then the sequence ends and an error message is displayed on the LCD panel MS30844V1 To save power during the Ipp measurement in low power mode run without the LCD LP and Halt modes the LCD is switched off Once the measurement has been performed it is then switched on to display the value of the power consumption Bias current record This operation consists in storing in the memory the value of the bias current inherent to the operational amplifier A see Figure 2 of your STM8AL board The value of the bias current is taken into account for low power measurements so as to minimize any mea
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12. erty of their respective owners 2012 STMicroelectronics All rights reserved STMicroelectronics group of companies Australia Belgium Brazil Canada China Czech Republic Finland France Germany Hong Kong India Israel Italy Japan Malaysia Malta Morocco Philippines Singapore Spain Sweden Switzerland United Kingdom United States of America www st com 16 16 Doc ID 023129 Rev 1 ky
13. figurations that can enable users to tune their products according to the application requirements It is advised to follow the power management recommendations outlined in the STM8L and STM8AL application note AN3147 Doc ID 023129 Rev 1 13 16 Conclusion AN4102 4 Conclusion The STMB8AL family of devices offers new opportunities for the automotive world and combines both a high performance core and an ultra low power management mechanism As more and more vehicles are being equipped with electronic components and since microcontrollers are much more present in automotive applications this induces additional energy constraints in particular for electrical vehicles Controlling and reducing the global power consumption of all these electronic elements is a new challenge for today s and tomorrow s automotive developments The STM8AL family can be a solution to drastically decrease the power consumption of a standard automotive system The example discussed in this document allows you to evaluate the current consumption of the STM8AL microcontroller in various operating conditions and to demonstrate its low power capabilities by directly providing the consumption value to the STM8AL board LCD panel More generally STM8A DISCOVERY provides a very low cost environment that can be used for additional automotive development projects The example shown here can be a useful starting point that can easily be expanded to investigate other as
14. ors The device is woken up from this mode by an external interrupt generated by the U7 counter Figure 6 HALT mode START HALT mode LCD disable RTC clock source none RTC clock OFF LCD clock OFF LSI disable Regulator ultra low power mode GPIO low power config Disable external counter U7 Halt Init function Y Enable external counter U7 Y HALT instruction Starts U7 counter that controls microcontroller wakeup Device in HALT mode Interrupt occurred MS30847V1 For further information refer to the application note STM8L family power management AN3147 Doc ID 023129 Rev 1 9 16 Software description AN4102 2 2 1 10 16 Software description STM8AL peripherals used by the application This application example uses the following STM8AL peripherals with the settings described below ADC The ADC performs analog to digital conversions of the internal reference voltage Vpp voltage display and of the voltage coming from the operational amplifier which is the image of the Ipp current e ADC resolution 12 bit e ADC conversion mode single e ADC sampling time 9 cycles TIMA TIM4 is used to generate the delays needed for display or wait loops GPIOs Port B is connected to the L99PM62GXP CAN and LIN driver not used in the low power demonstration sequence Port C and Port E are connected to the
15. pects of the user s target application especially when lowering consumption is of consideration 14 16 Doc ID 023129 Rev 1 ky AN4102 Revision history 5 Revision history Table 1 Document revision history Date Revision Changes 21 Dec 2012 1 Initial release Doc ID 023129 Rev 1 15 16 AN4102 Please Read Carefully Information in this document is provided solely in connection with ST products STMicroelectronics NV and its subsidiaries ST reserve the right to make changes corrections modifications or improvements to this document and the products and services described herein at any time without notice All ST products are sold pursuant to ST s terms and conditions of sale Purchasers are solely responsible for the choice selection and use of the ST products and services described herein and ST assumes no liability whatsoever relating to the choice selection or use of the ST products and services described herein No license express or implied by estoppel or otherwise to any intellectual property rights is granted under this document If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectu
16. rformed e MCU idle is the time during which neither MCU activity nor resources are required e MCU wakeup is the time necessary for the microcontroller to switch from the idle to the active state Typical sequence of a low power application tperiod MCU active MCU active tActive twu gt MCU wakeup MCU idle MCU wakeup MS30848V1 12 16 If we assume that the power consumption of these three phases is equivalent to IActive for the MCU active phase during tactive Iidle for the MCU idle phase during tidie e lwy for the MCU wakeup phase tw and that tperiog is the total time for these three phases then the Ipp average current can be calculated with the following formula lavg tactive X lActive tiaie Xlidiettwu Xlwu tperiod Doc ID 023129 Rev 1 ky AN4102 Managing power consumption in automotive applications For instance if one estimates the power consumption of an STM8AL MCU in the active phase of lactive 4 mA Run mode HSE oscillator F 16 MHz execution from Flash that lasts tactive 250 us a power consumption of ligig 400 nA STM8AL MCU in Halt mode with ultra low power ULP bit set during tidie 10 ms and finally a wake up from the HALT sequence where lw 2 4 mA during tw 4 7 us wake up from HALT to RUN mode using the HSI oscillator this corresponds to 250 x1079s x 4 x 10 A4 10 x 107 s x 400 x 10 A44 7 x 10 95x 24x 10 A
17. surement errors Doc ID 023129 Rev 1 X AN4102 Application description Once recorded this value does not need to be refreshed and is kept in the non volatile memory for future use It is recommended to perform this operation when you start your evaluation in order to obtain the best precision Figure 4 Bias current sequence START l BIAS displayed on LCD STM8AL board is not Set aa 1 powered yet Measuring This operation is done displaying and until the user ii recording Ibias removes the power current supply by disconnecting Press USER2 and the USB cable maintain it Y pressed Remove STM8AL Y board power supply Power supply STMBAL board Y LD4 ON Set JP2 ldd ENFIN ON Release USER2 button MS30845V1 1 6 Low power modes This section describes the low power modes used in this application example 1 6 1 Low power run mode without LCD In this mode the CPU and some of the peripherals are running The LCD and the RTC clock are disabled to save power and the GPIOs are placed in an output push pull configuration to limit consumption During low power run mode the code is executed from the RAM and the CPU is clocked by the LSI oscillator The Flash and data EEPROM are stopped and the voltage regulator is configured in ultra low power mode The microcontroller can be woken up from this power saving mode by an external event generated by a
18. t of its own operational amplifier When JP1 is placed in the OFF position Ipp measurement circuitry disabled a special test invoked by the USER2 push button at the device start up measures this current value and stores it in the non volatile memory Once this value is stored in the device it is deducted from the next Ipp measurement to compensate errors due to bias current see Section 1 5 2 Bias current record For additional information related to the Ipp measurement feature refer to the STM8A DISCOVERY user manual UM1574 Getting started with the application Two modes can be run within the STM8AL low power application example e lpp measurement in different power modes e Bias current record The Ipp measurement is available when the application is powered up with the USER1 push button pressed while the bias current record is available when the application is powered up with the USER2 push button pressed However for best performances it is recommended to control and record the bias current before starting the Ipp measurement mode IDD measurement Firstly check that JP2 is set to the ON position Before applying power to the STM8AL board through the USB cable or through an external power supply press the USER1 button and maintain it pressed while the USB cable is connected The Ipp mode is selected and the green LED LD4 is set The TEST message is displayed You are entering the Ipp measurement sequence Once
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