The solution of automotive body electronic control

2022-08-05
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Electronic control system solution of automobile body based on 16 bit controller

with the complexity of automobile body control application, the internal convection is eliminated, and the performance requirements of 16 bit microcontroller (MCU) are becoming higher and higher. The door control, seat adjustment, interior lighting and air conditioning systems previously realized by mechanical methods have now been changed to electronic control. In terms of such Futures: the iron ore 1605 contract was shaken and strengthened throughout the day. The electronic automobile body control system includes several main parts, such as power supply system, can transceiver, multi switch detection interface, output system, electronic motor control, embedded simulation and memory programming. This paper not only introduces a series of chips, but also will enable the design engineers to have a more general and comprehensive understanding of the automobile electronic control system

with the increasing complexity of automotive body control applications, the performance requirements of 16 bit microcontroller (MCU) are becoming higher and higher. The door control, seat adjustment, interior lighting and air conditioning systems that were previously controlled mechanically have now been changed to electronic control. A large number of special semiconductor solutions provided by many semiconductor manufacturers, including Motorola, make these new electronic control applications possible. These new solutions not only provide the necessary control functions, but also provide advanced diagnostic capabilities that the old mechanical systems cannot provide. Consumers hope that the control system in the new vehicle can send out alarm information in time for any system failure in the vehicle

this paper introduces the mc9s12dp25616 bit MCU and several peripheral IC products of Motorola. These products are designed to adapt to the harsh environment common in automotive systems. In addition, the advanced diagnostic functions provided by these products are also discussed in detail. Figure 1 shows a block diagram of the scheme used

I. power supply system

power supply system is one of the most important subsystems in any automotive system design. Overall power consumption, battery reverse pole protection, vehicle jump start, vehicle noise and vehicle sleep power are all factors that must be considered. If the power supply is poorly designed, the best system will not work properly. The intelligent power semiconductor products provided by Motorola can well manage all aspects of the power subsystem

Motorola's system level chip (SBC) mc33989 has two power rectifiers to provide power for MCU and peripheral devices. The chip also provides a can interface with a speed of 1 megabaud, four high-voltage wake-up inputs and system protection functions. This intelligent semiconductor device can provide all necessary system voltages. It has a low-noise 200mA rectifier inside to supply power to the MCU subsystem. In addition, there is a device that controls the external on transistor to supply power to peripheral devices. This external on transistor allows the secondary power supply to be adjusted to meet the power consumption limits required for each particular application. The secondary power supply can also cut off the power supply of the selected peripheral devices according to the requirements, so as to achieve the purpose of reducing power consumption

the input power is directly from the vehicle battery. Only one external diode is needed to achieve the purpose of battery polarity protection. The SBC can complete the protection action under all overvoltage conditions. The application of power MOSFET technology also enables the device to work normally when the battery voltage is as low as 4.5V. When the battery voltage is as low as 3V, it can output a battery fault alarm signal. The power supply system also has over temperature protection function. When the temperature reaches 160 ℃, internal thermal shutdown processing will be carried out. When the temperature reaches 130 ℃, an alarm signal will be output. In addition, the SBC can provide a low-power sleep mode in which the system current can be reduced to 40 μ A。

II. Can transceiver

in addition to providing system power supply, SBC also integrates a 1-megabaud can transceiver. The transceiver has the functions of master control status timeout detection, internal thermal protection, and can+ and can- input short-circuit protection. In the transceiver, can and can input terminals are also protected by jump start, battery reverse connection and short circuit to power or ground

4 high-voltage wake-up inputs make the device have a powerful wake-up function. The maximum withstand voltage of these wake-up inputs can reach 40V. The pull-up source at the input can be generated on the chip. Since the change of switch input can be detected at any time only by pulling up the source, the power consumption can be reduced. The device also has a periodic wake-up function. In addition, SBC also provides reset adjustment and low voltage detection functions for MCU

multi switch detection interface

due to the need for special contact wetting currents and circuit fault detection functions, automotive electronic devices need high complexity input sensing circuits to detect switch states. Motorola's multi switch detection interface (MSDI) device MC33993 is designed for this purpose

systems requiring a large number of switch interfaces have many discrete components, which occupy a large amount of space on the standard printed circuit board, and must be tested for solder joint connection integrity. The integration scheme can reduce the number of solder joints, occupy less space, and provide a wider working voltage, so it has greater flexibility. MSDI device performs switch detection function, which can detect the opening and closing states of 22 switch contacts at most, and these detected opening and closing states are transmitted to MCU through a high-speed serial link. The transient disturbance protection can be realized by adding a suitable electrostatic discharge capacitor at the input. Similarly, all input terminals have battery reverse connection, jump start and load disassembly protection functions

msdi also has optional wet current. These internal current sources greatly reduce the number of system components and make the use of metal or rubber switches possible. The large wet current used to detect metal switches can be selectively used in the detection process, so as to achieve the purpose of reducing power consumption. Using the internal current source, the input terminal can be used as the power supply for light loads, such as sensors, LEDs or MOSFET gates. This method further enhances the design performance of the system, so that these inputs can be used for other purposes without switch detection

analog circuits with high impedance are particularly susceptible to noise from other signals on the circuit board. Shortening the analog signal path and allowing the device to buffer the signal can reduce this effect. MC33993 has powerful analog interface function. Compared with traditional systems, this method can reduce system wiring and failure modes. In addition, MC33993 also integrates a 22:1 analog multiplexer to improve device performance. Channel selection is realized through a high-speed serial link. The device can not only provide advanced switch diagnosis function, but also allow the use of analog sensor interface and ladder impedance interface

mc makes more plastics with excellent performance become packaging materials. U output circuit can not directly drive automobile load, but also requires integrated circuits such as lamps, relays, motors, range meters and LED drivers. These special input interface devices also provide protection and error detection functions

output system

the output system must be considered after the power system and input adjustment are confirmed. Many automotive loads, including motors and lamps, cannot be directly driven by MCU or low current interface devices. Relays or mechanical switches are the main high current switching devices in today's automobile body control structures. Due to the low cost and mature design of the electromagnetic system, many system architects are still willing to use it. However, using electromagnetic system will cause many problems, such as:

1 The limited life of the mechanical contact limits the switching frequency of the relay. As the contact has certain inertia when it is opened or closed, it will jump to a certain extent before it stabilizes to the next state. This runout limits the maximum operating frequency. If the frequency is exceeded, the service life of the relay will be greatly shortened

2. The electromagnetic system has no diagnostic function. In the harsh automotive environment, the reliability of these devices is a big problem

these loads can be easily integrated into the system by using the drives specially designed for these loads. The mc33888 switch with 4 high-end and 8 low-end provided by Motorola is specially designed to drive automobile loads. This device can directly control 4 high-end loads with power up to 60W and 8 low-end loads with low current (2.5W). Mc33888 device also has built-in function to deal with surge current related to incandescent lamp. It can be seen from Figure 2 that the surge current caused by incandescent lamp can reach 10 to 15 times of the normal working current, which will bring great problems to the system without these large surge current processing circuits. The most common measure for such loads is to trigger the overcurrent protection circuit to cut off these loads

mc33888 solves this problem well. It uses a start timer to allow the incandescent lamp to preheat before the overcurrent protection circuit works. The startup of the overcurrent protection circuit needs to detect and adjust the state and pulse width signal from the output driver to the acceptable level of the device. Figure 3 shows the action waveform of overcurrent protection. The complete battery reverse pole protection, load dump protection and low power consumption features help to reduce the complexity of the system and the number of external components. The diagnostic functions include load open circuit detection, short circuit detection and over temperature detection. As an additional protection function, the device also has a built-in watchdog timer, which can be used to shut down the device when the communication between the device and MCU is interrupted. The control of the device is realized through a high-speed serial interface, so the number of MCU pins is greatly reduced

electronic motor control

the last issue to consider is electronic motor control. Mc33887 motor driver can accomplish this task well. Chapter 4 "combustion performance grade", Chapter 5 "combustion performance grade criteria" and chapter 6.1 "combustion performance grade identification" of the new national standard are mandatory standards. It is a complete H-type bridge driver. The device has a continuous current drive capability greater than 5a, so it is very suitable for locking motor, antenna motor or wiper pump. Mc33887 also has high-end current sensing feedback function. The high-end current sensing feedback function can correct the drive frequency and load cycle of the motor according to the real-time motor current feedback. Just like the lamp driver, it can automatically pulse width modulate the output when the overcurrent state is detected

mc33887 device can completely control the H-bridge activation direction and load interrupt control

embedded emulator

MC33993, mc33887 and mc33888 devices specially designed for complex automotive electronic applications provide solutions with advanced performance and diagnostic functions

complex multi pin MCU often causes development problems. MC9S12DP256 provides a single line background debugging interface, which can easily realize a wide range of debugging work in the automotive environment, and will not encounter the common difficulties when using the traditional circuit embedded simulator. This interface can also be used to program the main flash memory at the end of the production line, or even to perform reprogramming operations in the vehicle

modern automobile microcontrollers often use flash memory to store the main operating program. The best way to program flash memory is to program the main program into a complete electronic control module after final assembly. Compared with programming the main program into MCU through a third party before module assembly, this method can effectively avoid risks and delays. The main program is programmed into MCU through a simple serial interface

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