The new in-vehicle infotainment system and navigation system provide more content, allowing you to experience higher quality audio and video programming and improve the connectivity of personal communication devices. In order to adapt to the high data transmission rate and meet the requirements of current communication, the device should be protected from damage caused by customer misuse, dangerous environment and power fluctuations.
Self-resetting PPTC (Polymer Positive Temperature Coefficient) devices are widely used in infotainment systems to protect precision electronic components and peripherals. In applications where the self-recovery function is not desirable or practical, a chip surface mount fuse is typically used.
Infotainment devices are also susceptible to damage due to excessive transient voltages, including the working environment in which they are located and the electrostatic discharge (ESD) pulses generated by peripheral devices. ESD protection devices, metal oxide varistors (MOVs) and Zener diodes are commonly used to protect automotive electronic devices such as antennas, backlight heaters, batteries, buttons, printed circuits on circuit boards, CD/DVD players, data lines Ports, hard drives, and input/output ports and touch screens.
Design considerations for automotive circuit protection devices:
1, PPTC overcurrent / overheat protection. The popular PPTC device has a self-resetting function that can be mounted in an easily accessible location in a car. It has a wide range of products with different electrical properties and sizes to facilitate a variety of precise protection designs. When selecting a PPTC device, the main consideration is that the device's holding current rating is matched to the primary current of the device during normal operation.
2. ESD protection device. High-speed input/output ports require the use of small-capacitance ESD protection devices to keep signal quality as low as possible. The device chosen should be suitable for high-speed data transmission lines and radio frequency data lines, capable of withstanding numerous ESD transients. To meet the requirements of RoHS and IEC61000-4-2, the capacitance is small, the trigger voltage is low, and the response time is short. These are also important features of ESD protection devices.
3. Surface mount fuses. The surface-mount fuses with large current and small size have two products that are fast and slow, and their fuse characteristics should be clean and neat, and the entire fuse process is carried out in the package. Their ability to suppress arcing should be good and able to withstand shock and vibration.
4. Metal oxide varistor. Metal oxide varistors (MOVs) are available in a variety of diameters and voltage ranges. MOV devices can flow a large amount of current and absorb a large amount of energy to achieve overvoltage protection. When selecting MOV, it is mainly based on the clamp voltage level (suppressed voltage rating) and response time.
5. Protection of DC power port. The car power bus is very dirty, which is known to everyone. The car's power supply is rated at 12V, but will change from 8 to 16V during normal operation. Also, the current of the battery will exceed 100A, and it will be interrupted by the action of the relay or the fuse is blown. Therefore, a large induced voltage spike is generated on the power bus, and the voltage is increased by more than 5 times.
During the operation of the car power supply, it may be damaged due to the wrong connection of the battery or the connection of the battery with twice the voltage (24V) when the dual battery is started. There is a situation called "load dumping" which can generate very high voltages on the power bus. A typical third-party power converter will filter it out, but tests by Tyco Electronics show that the ability of these power converters to reject transient voltages varies greatly. Devices that typically charge the USB interface are generally not designed for this type of voltage fluctuation and therefore require overvoltage protection.
In automotive applications, the current can be very large, so be careful and ensure proper protection. For the selected device, check its IFLT maximum and Vout peak to ensure that the device provides the required protection.
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