TLE7810's unique SBC low power design method

　　introduction

　　In recent years, with the development of electronic technology, information technology and the popularization of digital products, embedded systems have been widely used in various fields such as automobile industry, network, handheld communication equipment, national defense and military, consumer electronics and automatic control. At the same time, the power consumption problem in embedded system design is also receiving widespread attention. Embedded systems are generally powered by batteries. The system adopts low-power design, which can not only extend the life of the battery, but also reduce the heat consumption of the system, which is of great significance to improving reliability and stability. In this application context, well-known single-chip microcomputer manufacturers such as Infineon, Freescale, Atmel, TI, etc. have launched powerful low-power single-chip microcomputers.

　　1 Sources of MCU power consumption

　　The microcontroller is a highly integrated chip. Usually, the power consumption of an integrated circuit is divided into two parts: static power consumption and dynamic power consumption. Static power consumption refers to the constant state of "0" and "1". When the circuit does not flip, the power consumption is static power consumption; dynamic power consumption refers to the jump state of "0" and "1". When the circuit flips, the power consumption is dynamic power consumption.

　　At present, most single-chip microcomputers use CMOS technology. CMOS circuits are voltage-controlled and generally have very low static power consumption. Its dynamic power consumption consists of two parts: instantaneous on-state power consumption and capacitor charging and discharging power consumption. When the single-chip microcomputer is running, the switch circuit continuously changes from "1" to "0" and from "0" to "1", and the internal capacitor is constantly charging and discharging. To achieve fast shutdown of the switch circuit and fast charging and discharging of the capacitor, a relatively large dynamic current is required [3]. Therefore, the dynamic power consumption of CMOS is much greater than the static power consumption and is the main source of power consumption of the single-chip microcomputer. Dynamic power consumption is mainly affected by the operating frequency and operating voltage.

　　Through the analysis of the power consumption sources of the MCU, it can be concluded that to reduce the power consumption of the MCU system, the method of reducing the operating frequency, reducing the operating voltage and keeping the circuit in a static state as much as possible can be adopted. In fact, the existing low-power MCUs also provide flexible clock schemes, power management schemes, and low-power working modes, which make it possible to reduce the operating frequency, reduce the operating voltage and keep the circuit in a static working state in hardware.

　　2 TLE7810 Introduction

　　TLE7810 is a highly integrated, low-cost intelligent power chip launched by Infineon, mainly used in the automotive industry. Its functional module diagram is shown in Figure 1. It integrates an 8-bit microcontroller XC866 that supports on-chip debugging and is compatible with the standard 8051 microcontroller, as well as an SBC (System Basis Chip). Such a structural design can meet the most demanding application conditions in the automotive industry. Similar to microcontrollers from other manufacturers, Infineon XC866 also provides flexible clock solutions, power management solutions and low-power working modes. This article will not introduce these functions in detail, but will focus on the low-power design of the SBC unique to TLE7810.

Figure 1 TLE7810 functional module diagram

　　As can be seen from Figure 1, the SBC is equipped with a LIN transceiver, a low-dropout voltage regulator, two low-side switches for driving relays, a high-side switch for driving LEDs, a Hall sensor power supply, five wake-up inputs, and a standard 16-bit SPI (Serial Peripheral Interface) interface. Through the SPI interface, the XC866 can send a 16-bit command to control the operation of the SBC, and the SBC will reply to the XC866 with a 16-bit data to indicate the current operating status of the SBC. [page]

　　3 SBC low power design solution

　　3.1 SBC Integrated Peripherals

　　SBC not only integrates multiple peripherals into one chip, but also can control the opening and closing of these peripherals through the SPI interface. According to the actual application situation, these peripherals can be flexibly controlled to achieve the purpose of reducing power consumption.

　　① LIN transceiver. The operating mode of the SBC can be set to "LIN Sleep" mode via SPI commands. In this operating mode, the internal pull-up resistor of the LIN transceiver is turned off to disable the LIN transceiver, which can reduce some current consumption. The disabled LIN transceiver can be activated at any time via a LIN message from the master node or other slave nodes.

　　② Low dropout voltage regulator. The SBC operating mode can be set to "Sleep" mode through SPI commands. In this operating mode, the voltage regulator is turned off to stop powering the microcontroller, so that the system enters a sleep state and minimizes power consumption.

　　③ High-side switch. The high-side switch can directly drive the LED. When the LED is not needed, the switch can be turned off directly through the SPI command.

　　④ Hall sensor power supply. This power supply can directly power the Hall sensor to drive the Hall sensor to work normally, and can also power some other devices, such as operational amplifiers. When the Hall sensor is not needed, the power supply can be turned off directly through the SPI command.

    3.2 SBC power saving mode and wake-up test

　　SBC can work in multiple working modes and can flexibly switch working states according to actual application conditions. SBC provides two power saving modes, "Sleep" mode and "Stop" mode. Working in these two modes can greatly reduce the power consumption of the system.

　　3.2.1 SBC Sleep Mode

　　This working mode can be entered by directly modifying the SPI command. In this working mode, the LIN transceiver and all internal switches are turned off, and the internal voltage regulator is also turned off to stop powering the microcontroller. In this way, the power consumption of the system can be minimized. The system can be woken up by a level jump on the five wake-up input pins or a LIN message. After being woken up, the internal voltage regulator will be automatically activated, and the microcontroller will generate a reset signal to reset the system. Figure 2 shows the test waveform of the "Sleep" mode. Among them, curve 1 is the waveform of the wake-up input pin MON4, and curve 2 is the waveform of the reset pin RESET. In the "Sleep" mode, the input of the MON4 pin is a 12 V high level, and the RESET pin outputs a 0 V low level. When the level of the MON4 pin jumps from a high level to a low level, the RESET pin generates a 5 V high level reset signal to wake up and reset the system. It can be seen from the figure that this wake-up time lasts about 9.5 ms. According to further measurements, the static current of the system in this mode is about 9 mA.

Figure 2 SBC Sleep Mode test waveform

　　3.2.2 SBC Stop Mode

　　You need to set the working mode of XC866 to power saving mode first, and then modify the SPI command to enter this working mode. In this working mode, the LIN transceiver and all internal switches are also turned off, but the voltage regulator is not turned off. Instead, a weak static current is used to power the microcontroller, and the microcontroller stops executing instructions at the same time. This mode can be exited through a level jump on the 5 wake-up input pins or a LIN message. Figure 3 shows the test waveform of the "Stop" mode. Among them, curve 1 is the waveform of the wake-up input pin MON4, and curve 2 is the waveform of the output pin P0.5. In the "Stop" mode, the input of the MON4 pin is a 12 V high level, and the P0.5 pin outputs a 0 V low level. When the level of the MON4 pin jumps from a high level to a low level, the system is awakened, and then the P0.5 pin immediately outputs a 5 V high level. It can be seen from the figure that this wake-up time lasts about 265 μs. According to further measurements, in this mode, the static current of the system is about 30 mA. Compared with the "Sleep" mode, this mode can not only greatly reduce the system power consumption, but also because the microcontroller is not turned off, the system can be woken up faster. After waking up, no reset signal is generated and execution continues directly from the stopped instruction position.

Figure 3 SBC Stop Mode test waveform

　　4 Application of TLE7810 low power solution

　　A specific application of TLE7810 is the electric window controller. The hardware structure block diagram of the electric window controller based on TLE7810 is shown in Figure 4. Among them, the high-side switch (MON5 pin) is used to power the key backlight, and the Hall sensor power supply (Supply pin) is used to power the Hall sensor and the operational amplifier at the same time. [page]

Figure 4 Electric window controller hardware block diagram

　　The output levels of the MON5 pin and the Supply pin are directly controlled by the SPI command. When the four buttons (MON1~MON4) that control the window lifting and lowering are not pressed, the MON5 pin is controlled by the SPI command to output a low level, and the button backlight is off; when a button is pressed, the MON5 pin is controlled by the SPI command to output a high level, and the button backlight is on. When the motor is in the stopped state, the Supply pin is controlled by the SPI command to output a low level, and the power supply to the Hall sensor and the operational amplifier is turned off. The Hall sensor measures the speed and direction of the motor when the motor is running, and the operational amplifier is used to sample and amplify the motor current. Therefore, when the motor is in the stopped state, these two peripherals do not need to work. Turning off their power supply can reduce power consumption to a certain extent.

　　When the rear door window does not receive any control command from the rear door button, nor does it receive any command from the driver's door through the LIN bus, the system can be directly put into "Sleep" mode through the SPI command after a delay. In the normal working mode of the window controller, the system current is about 150 mA. In this mode, the power module inside the TLE7810 stops supplying power to all loads, and the system current is only 9 mA, which minimizes the power consumption of the controller. After sleep, if the driver's side or rear door button re-issues a command, the system can be awakened and enter normal working state.

　　5 Conclusion

　　This article analyzes the source of microcontroller power consumption, takes the Infineon TLE7810 microcontroller as an example, studies the low-power design of the SBC unique to the TLE7810, and briefly explains the practical application of the TLE7810 low-power design in combination with the example of a specific electric window controller. In complex practical applications, it is also necessary to comprehensively consider the system hardware design corresponding software, and select the appropriate low-power design in combination with the specific application scenarios to achieve the purpose of reducing system power consumption.