september 2013 docid024014 rev 2 1/26 AN4218 application note hardware design guideline power supply and voltage measurement introduction this document provides useful hints and suggestions about the implementation of the stmicroelectronics 32-bit microcontroller devices in an automotive system. the main focus has been set on the power supply concept and the connection to signals from different power domains. due to the harsh conditions in the automotive environment several precautions have to be taken into account to ensure the robustness of the system. this is especially important when defining its power supply concept. this document shows test cases defined by car makers, which are intended to reproduce the system behavior in the real automotive environment, it also shows good practices to cope with them as well as bad practices and their influence on the system robustness. www.st.com
contents AN4218 2/26 docid024014 rev 2 contents 1 system overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 car-battery power supply (vbat) transients . . . . . . . . . . . . . . . . . . . . . . . 6 1.2.1 example battery supply test pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.2 power-up-reset requirements of the spc microcontrollers . . . . . . . . . . . 8 2 good practices of system power supply . . . . . . . . . . . . . . . . . . . . . . . 10 2.1 microcontroller power supply reactions on vbat transients . . . . . . . . . . 10 2.1.1 l99pm62gxp block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.2 measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.1.3 measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3 application circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1 reference circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2 implementation suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2.1 measurement of an permanently enabled power-supply (vmeasure) 16 3.2.2 bad practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2.3 physical layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 appendix a reference documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
docid024014 rev 2 3/26 AN4218 list of tables list of tables table 1. parameters sharp test pulse e11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 table 2. vdd ramp specification (spc560p34x, spc560p40x ? example only). . . . . . . . . . . . . . . . 9 table 3. document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
list of figures AN4218 4/26 docid024014 rev 2 list of figures figure 1. microcontroller with power supply, drivers and physical layer . . . . . . . . . . . . . . . . . . . . . . . 5 figure 2. brown out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 3. non strictly rising ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 4. slow ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 5. residual voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 6. test pulse e11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 figure 7. vdd ramp-up/ ramp-down (spc560bxx, spc560cxx, ? example only) . . . . . . . . . . . . . . . 9 figure 8. l99pm62gxp block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 figure 9. measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 figure 10. engine cranking pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 figure 11. measurement over the entire pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 figure 12. zoom into the low voltage drop region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 figure 13. vs voltage ramp up (0.5 v/min) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 figure 14. vbat voltage ramp down (0.5 v/min) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 figure 15. reference circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 figure 16. voltage divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 figure 17. iso transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 figure 18. negative iso-pulse simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 figure 19. protection and low-pass-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 figure 20. amplitude and phase over frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0 figure 21. backward current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 figure 22. bad example circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 figure 23. can-transceiver without reverse protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
docid024014 rev 2 5/26 AN4218 system overview 1 system overview 1.1 overview figure 1 shows a system, consisting of a microcontroller, a system basis chip, a physical layer transceiver and load drivers. the system-basis-chip (sbc) generates the power-supply for the other devices in the system and communicates via serial-parallel interface (spi) with the microcontroller (spc- c). the physical layer transceiver (e.g. standalone can-transceiver) is supplied by the sbc and transfers data from and to the microcontroller via logic-level signals. through the can- bus it is connected to other can-transceivers in the car, which have their own independent power supply. dedicated drivers for high-power loads (light-bulbs, leds, door locks, mirror folds, h-bridge drivers etc.) are also connected to the microcontroller power supply and communicate with it by spi. several peripherals of the microcontroller are used to monitor voltages like the battery voltage, either by a logic-level input/output or an analog-to-digital convertor (adc). the inductances ls1 to ls4 are the parasitic wire inductances of the supply lines. capacitances are added to either protect the supply against distortions or to stabilize the voltage generated the by voltage controller inside the sbc. protection resistors are added at the monitor inputs of the microcontroller. figure 1. microcontroller with power supply, drivers and physical layer 9 ' ' 9 % $ 7 & 9 % $ 7 & 9 % $ 7 & 9 ' ' w r o r d g 9 % $ 7 & |