Many multi-applications in the car, from the car's light bulb to the relay, from LED display lighting to the starter motor, not only provide a wide range of high-load, low-cost solutions, but also focus on safety. The communication and diagnostic capabilities necessary for the car. Therefore, in order to increase the reliability and durability of the electronic system on the vehicle, the designer added fault protection circuits to the power device in addition to reducing the maintenance cost, avoiding the failure of the assembly and reducing the damage caused by the electronic system.
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In addition, in the case of a general automobile driving, once a component failure condition occurs in the vehicle, a short circuit may occur in the circuit system of the automobile, or the power supply may not be powered. After using the MetalOxide Semiconductor Field Effect Transistor (MOSFET) component technology in the remote sensor, it will be able to timely protect the failed component or form a high impedance between the automotive wiring harness and the faulty component. Reduce the incidence of failures.
Automotive MOSFET components and self-protection technology
To some extent, new models have been designed with electronic circuits designed to reduce cost, increase reliability and enrich functionality. On the other hand, with the increasing number of electrical and electronic systems and the fact that they take up most of the cost and weight of the car, this design makes circuit protection design a key part of the design effort. Therefore, most automotive design engineers use external sensors, discrete circuits or software for the application of automotive components. However, with the continuous development of technology, MOSFETs have the advantages of high frequency performance, high input impedance, low driving power and excellent thermal stability. They also enable power components to meet the lowest system cost and can be classified into multiple loads. In a conductive single-pole voltage control unit. Therefore, many designers will use a protective power component such as MOSFET to complete the design.
Caption: The general automotive circuit system architecture can be roughly divided into two types, embedded and convenient ports. The technical specifications used in the current technical specifications define the specifications of MOSFET components.
In the past few years, electronic equipment has been installed inside and outside the automobile, and the number of automobile manufacturers that control the function of the automobile main body has continued to increase rapidly, and the number of applications for automotive semiconductors has also been significantly improved. In a complex automotive electronic system, almost all power components used can respond to rapid changes in the environment, in the face of the transient current caused by the shutdown of the electronic product, and the high voltage change caused by the failure of the load to cut off the power supply. There is a way to respond.
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In addition, when the ambient operating temperature in the car exceeds 100 ° C ∼ 120 ° C (such as: engine room, tires, etc.), it is easy to produce the junction temperature of the component, which affects the reliability of the component. Degrees and other problems that may occur. Another problem is the complicated wiring harness problem in the car. There are many connectors in the vehicle wiring harness. Because there are more and more power requirements in the car, even under normal application conditions, the pressure on the components is relatively increased. It is also very likely to cause intermittent faults in the electrical connection of components.
In order to meet the greater current demand of automobiles, in line with the current trend, automotive semiconductor manufacturers must develop power MOSFET component technology. In order to reduce the resistance value when current flows, MOSFETs have been used more and more in automotive electronics and power systems, so that the importance can be seen. At this stage, in order to achieve more efficient energy utilization and the lowest cost application advantages, in addition to meeting the ever-changing application environment of the vehicle, it is also necessary to comply with the requirements of international formation standards, so as to further meet the requirements of the automotive market for power formation. . Therefore, while designing the power system for automotive electronics, automotive electronic design engineers face a variety of difficult technical difficulties in addition to their own problems of suitability, reliability and durability.
Caption: As power demand increases, the complexity of the harness is increased, and the wiring, weight, and packaging limitations of the car are increased. Therefore, each electrical circuit requires adequate circuit protection for short circuits and overloads. Although each electrical load can theoretically be protected by its own dedicated fuse, the fuse must be replaced after it has been blown.
What other problems remain in the automotive electronics system?
â—Ž short circuit fault problem in the car system
If there is a short-circuit fault between the components of the on-board circuit system, the MOSFET will be immediately turned off, and the short-circuit current will be shunted around the MOSFET, and it is easy to find the fault problem. However, once the short circuit of the circuit system is intermittent or the load is an inductor, a flyback voltage (Flyback) is generated on the MOSFET to determine whether the peak current in the load inductor is higher. Peak current during normal operation. Therefore, the energy absorbed by the component will be more than originally expected, and multiple intermittent short-circuit conditions will also occur continuously and quickly, which will lead to a rapid increase in peak junction temperature and easy potential for the component itself. The destruction.
â—ŽThe temperature is too high and it is easy to malfunction.
The electrostatic discharge (ESD) of the component pins, the instantaneous current of the line, and the inductive load switch generate excessive pressure, and the other is the problem of overheating. In many devices, once the temperature of the component is overheated, it is easy to cause a fault or even cause other components to malfunction. Just like the short circuit of the circuit system, it is easy to make the component consume excessive power, or in the extremely cold and extremely hot environment, the soldering between the heat dissipating device of the component or the circuit board may be invalid. In such a large number of possible failures, the control circuit with self-protecting MOSFET components is monitored in a safe mode, even to control the operation of the component. Once the component temporarily fails, it can be repaired and restored immediately. The normal function can even further reduce the size of the control components on the car, and also improve the reliability, while the sensor has self-fault diagnosis, working condition monitoring and temperature sensing, over voltage and over current protection. Features.
Caption: The output system of automotive electronics also needs to protect itself from overcurrent caused by short circuit or motor stall. Therefore, MOSFET is designed with high frequency performance, high input impedance and low driving power. Design method with excellent thermal stability.
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How to achieve self-protection when the temperature is too high
In a typical car, the over-temperature protection component used is implemented using a temperature-sensitive component such as a diode bias. Assuming that the above components monitor the junction temperature of the chip beyond the value set at the beginning, the circuit system will pull the gate of the MOSFET with the main power to ground, and close the component at the first time to make part of it. The built-in component can suspend the current transfer action and wait for the current to reach the normal state after the temperature of the chip drops slightly to the appropriate temperature.
After a high temperature fault, there are two main issues that must be addressed.
First, when the equipment is continuously operated, the temperature of the component is too high, which may cause the self-protection to fail, and the possibility of component failure may occur. This is because when the inductive load or the transformer load is turned off, the output power of the output will vary and change due to the difference in frequency. At this time, the circuit components will actively absorb the energy stored in the load inductor, which is applied to Automotive electronics, circuit system MOSFET standard component system is very important. Because, once the junction temperature exceeds the temperature that the internal temperature can withstand, the component no longer has semiconductor characteristics, and the gate control action is prone to error conditions unless the drain power supply immediately disappears. When the transistor gate length is shortened, the threshold voltage is caused. The (thresholdvoltage) is thus reduced, which in turn produces a short-channel effect that will damage the circuit components of the device.
Self-protected MOSFETs can suffer from the same situation because when the gate input voltage biases the control circuit, the overtemperature limit circuit is inactive because the gate bias is zero. In normal operation and worst-case fault conditions (such as intermittent short-circuits in devices), the circuit designer must ensure that the energy absorbed by the device does not exceed the maximum rating. In addition, even if the highest energy rating occurs, there must be sufficient time between the energy pulses to cool the junction temperature to the initial junction temperature. Otherwise, the junction temperature rises after each energy pulse and eventually reaches the internal fault temperature.
Second, when the temperature limit switch circuit and the current limit circuit work together, there is a possibility of high temperature failure. When the current generation limiting circuit increases the voltage of the gate node to the vicinity of the threshold voltage, and forces the component into the working mode, and generates different parameter values ​​and analyzed data results under different component structures, thus The set point that maintains the current limit meets the characteristics of high current and low power consumption at any time to meet the automotive electronic system that evolves from mechanical form to electromechanical form.
For components that use a thermal hysteresis circuit to cycle the components on and off in the event of an overtemperature fault, the junction temperature will stabilize at the temperature between the high and low setpoints of the hysteresis circuit. This is similar to the high temperature reliability test and depends on the operating time of the component in the event of a fault. In general, when the reliability of a component becomes a problem of concern, do not expect the component to operate for thousands of hours or more in the event of a fault.
Caption: The future of automotive circuit architecture will transform the 42V PowerNet power supply network and the transitional dual voltage network, providing many opportunities for innovation in electrical and electronic system architecture.
For automotive power, electronic equipment control systems, fault self-detection, signal processing, etc., MEMS also has an important symbol of the times. In the power interface, it also needs to have the self-protection function of overcurrent to the battle line electronic electronic Chenye system. The imported power standard protects the part of the vehicle's power supply in order to prevent various types of faults from occurring. To prevent various types of failures from occurring. Therefore, in the automotive application, the future of micro-electromechanical will continue to develop, including power technology, such as power, microelectronics, and electronics in the car, so more power and electronics suitable for use in automobiles. The establishment of a self-protection system will be developed by engineers.
The current limit on the car can be achieved using resistors, fuses, switches or MOSFET component technology. Resistance protection schemes are rarely used today because they generate excessive voltage drops under normal current conditions. It is possible to use a one-time fuse solution, but this protection is prone to damage and must be replaced after a fault has occurred. The limitation of the bimetal switch is that it is repeatedly turned on and may cause contact fusion failure. In many automotive applications, the best protection scheme is MOSFET component technology, which exhibits low impedance under normal operating conditions and high impedance in the event of a fault; thus, the automotive power self-protection system can be presented. Optimized state.
Because the car is prone to short-circuit components during power-up or shutdown, the most common and troublesome problem in the car is the "short-circuit" problem in the automotive circuit. It can also be said that most of the short-circuit faults generated in automobiles are intermittent, that is, many different conditions may occur in a short time, but MOSFET components can now be utilized to solve such circuit system short-circuit problems.
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