introduction
Every revolution in the information age has brought about tremendous changes in human life. As the emerging information revolution, The Internet of things has become the new darling and development direction of the entire information industry. The Internet of Things is the Internet connected by objects. It is connected to the wireless network through interfaces such as radio frequency identification (RFID), sensors, and two-dimensional codes. It can give people "smart" and realize people and objects. The interaction can also realize the communication and dialogue between objects and objects. This network that connects objects is called the “Internet of Thingsâ€.
IoT awareness protection requirements
The structure of the Internet of Things itself is complex, mainly consisting of three parts: first, the perception layer, which undertakes the collection of information. The applicable technologies include smart cards, RFID tags, identification codes, sensors, etc., followed by the network layer, which undertakes the transmission of information. The existing wireless network, mobile network, solid network, Internet, and wide-area network can be realized; the third is the application layer, which realizes the recognition and perception between objects and objects, and plays an intelligent role.
The perception layer solves the problem of data acquisition in the human world and the physical world. The main function is to identify objects and collect information, similar to the role of skin and facial features in the human body structure. It first collects data from the external physical world through sensors, cameras, RFID and other devices, and then transmits data to the network through technologies such as Bluetooth, wifi, and 3G. 1 is a schematic structural view of a multi-function handheld terminal.
Figure 1 Schematic diagram of multi-function handheld terminal frame structure
Many devices in the IoT awareness layer have been widely used in police law enforcement, large commercial enterprises, chain stores, fast-selling goods sales, medical care, factory assembly lines, logistics, hotel catering, convention centers, and public transportation. Due to the complicated and harsh conditions in use, the product life and reliability requirements are very high. In design, manufacturers must make perfect circuit protection measures to meet the reliability and stability requirements of users.
From a design perspective, designers must take into account the unexpected occurrences of various conditions and then install protection devices on different interfaces. In this article, we will use a multi-function handheld terminal as an example to illustrate how to use a protection device.
IoT awareness layer device power interface protection
A stable power supply is the most basic condition for the normal operation of the device. However, the environment of the power interface is very complicated. Users may encounter the following situations: Since more adapters are used together, a low-voltage power supply device is incorrect. When the adapter is connected to a high voltage, even the polarity of the interface is reversed; or during the normal charging process, a very high surge voltage is generated at the output of the adapter due to the induced lightning. Events such as this will damage the device's power management chip.
For overvoltage and surge events that may occur, designers often use overvoltage protection integrated circuits or TVS tubes for protection. Although the integrated circuit OVP solution can solve the overvoltage problem, it does not have surge protection. While the TVS tube can achieve surge protection, it cannot be effectively protected when it is in a long-term overvoltage condition. The ideal situation is to combine long-term overvoltage and surge protection on a single device.
Poly Conen products from TE ConnecTIvity's Circuit Protection Division provide overvoltage, surge, overcurrent, overtemperature, ESD protection, and reverse power protection, as well as a separate recoverable fuse (PPTC) and regulated The higher performance, more protection and smaller size of the tube/TVS tube combination circuit has been proven in a variety of handheld and in-vehicle multimedia devices.
When an overvoltage fault condition occurs, after the clamp diode is broken down, its temperature will rise continuously with time. If the fault is not eliminated, or a long time overvoltage fault pulse is loaded on the circuit, this The use of low-power TVS devices does not provide effective protection, requiring high-power TVS devices to protect the back-end electronics, while high-power TVS devices mean more expensive prices and larger package sizes. The PPTC integrated in TE's PolyZen device enables fast and effective overcurrent protection. When the fault occurs, the temperature of the Zener rises. Due to the unique thermal coupling characteristics of the Zener and PPTC, the temperature of the Zener can be transmitted immediately. To the PPTC body, the PPTC itself is a thermal element, which can operate in a short period of time and become a high-impedance state, so that the current of the entire circuit is limited, and the fault voltage is shared by the PPTC and the Zener. Withstand, the Zener tube is well protected. PPTC can withstand fault voltage for a long time, so that PolyZen can handle a long-term continuous overvoltage and overcurrent protection. This unique feature of PolyZen devices enables it to withstand large energy surges and long-term overvoltage protection in a small package size. Figure 2 is a schematic diagram of the structure of the PolyZen device. Figure 3 is an electrical schematic of a typical input interface protection circuit for a PolyZen device.
Figure 2. PolyZen device schematic block diagram
Figure 3 PolyZen device in a typical input port protection circuit
ESD protection for IoT awareness devices
IoT awareness devices also require electrostatic discharge (ESD) protection. Below are some modules or interfaces that need to be protected.
First, the touch panel module. The touch panel is touched with a finger and is highly susceptible to ESD interference. In PCB design, SESD can be added to the connector position where the flexible board leads to effectively protect the ESD static generated through the connector. In addition, there is an ESD risk from the edge shielding layer of the touch panel when the terminal is used. Therefore, the SESD device should also be installed between the shielding layer and the ground line to avoid signal interference on the one hand, and to effectively clamp the circuit system voltage on the other hand. . A single SESD is used between the power line and ground, and the other ports are protected by a SESD array.
Second, GPS, RF antenna part. Lightning in the natural environment or ESD in the human body and the environment has the opportunity to discharge into the device through the RF and GPS antennas, causing damage to the electronic components at the receiving end of the antenna. Since the RF signal is very sensitive to capacitance values, SESD components with capacitance values ​​below 0.3pF are suitable for antenna part ESD protection. In the PCB design, the SESD component should be placed close to the antenna as much as possible, and it can effectively achieve protection by using the lower clamping voltage and high surge current resistance of the front end component.
Third, the button part. Since the user needs to directly touch these physical buttons to operate, the ESD phenomenon often occurs in the gaps of the physical buttons. The design of the SESD component should be placed close to the button contact as much as possible, and it can effectively achieve protection by controlling the lower clamping voltage and high abrupt current of the IC component than the front button.
Fourth, the user interface part, such as USB interface, SIM card, TF card, etc. Users will often operate these interfaces, and each time they are plugged in, they will cause ESD problems. Therefore, it is necessary to adopt the necessary ESD protection. The USB interface speed is very fast, so it is required to maintain signal integrity after adding SESD protection. TE's low-capacitance SESD The device can be protected by USB port. For the SIM card and TF card interface, since the signal rate is not high, the SESD array using a common capacitor can be protected.
For the SESD industry trend in low-capacitance and ultra-small packages, TE offers a range of products for designers to choose from. TE has achieved the smallest capacitance (0.1pF) and minimum package. Table 1 is TE's SESD low-capacitance products. .
Table 1 TE company SESD low capacitance products
Review
For the power port protection of IoT-aware devices and the ESD static protection of each module or interface, TE has a complete set of solutions. For IoT circuit protection solutions, you can visit TE's portal or contact TE Circuit Protection for more detailed technical support.
This article is selected from the "Internet of Things Conference Journal", please indicate the source.
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