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Application advantages of TVS diode in portable device ESD
Publish：SHENZHEN ENXIC ELECTRONICS CO., LTD,Schottky diodes, rectifier diodes, fast recovery diodes, switching transistors, thermistors, MOS tube, TVS tube, Youze Electronics Time：2018-01-04 Views:1245
Portable devices such as notebook computers, mobile phones, PDA, MP3 players, and so on, because of frequent contact with the human body are vulnerable to the impact of electrostatic discharge (ESD), if no appropriate protection devices are not selected, the performance of the machine may be unstable or damaged. Worse is that it can‘t find out the exact reason, which makes the user mistake the product quality and damage the reputation of the company.
Therefore, the ESD protection of the portable equipment is very important, and the TVS diode is a very effective protective device. Compared with other devices, it has its unique advantages. But in application, the device should be selected for different protective objects, because different ports may be subjected to different electrostatic shocks and different devices. The degree of protection is also different. Attention should be paid to the corresponding parameter identification and the different design of each manufacturer, and at the same time, a reasonable layout of PCB should be made. This paper introduces the advantages of TVS diode in portable device ESD.
In general, anti - static protection, such as keyboard, power interface, data port, I/O port and so on, is required to protect the port which may be exposed to the human body. Now the common ESD standard is IEC61000-4-2, using the human static mode, the range of the test voltage is 2kV to 15kV (air discharge), the peak current is 20A/ns, and the duration of the whole pulse is not more than 60ns. The energy generated by such a pulse does not exceed hundreds of micro Joule, but it is enough to damage sensitive components.
Most of the IC devices used in portable equipment are highly integrated and small volume products. The precision processing technology makes the silicon oxide layer very thin, so it is easier to break through, and some of them will be damaged around 20V. Traditional protection methods are no longer widely applied, and some may even cause interference to device performance.
Advantage of TVS diode
TVS and zener diode: compared with the traditional zener diode, the TVS diode has a larger P/N junction area. This structural improvement makes the TVS more capable of high voltage endurance and reduces the voltage cut-off rate, and thus has a better effect on protecting the safety of the low working voltage loop of the handheld devices.
TVS and ceramic capacitors: many designers are willing to use ceramic capacitors with surface mount as ESD protection, which is not only cheap but also easy to design, but the bearing capacity of these devices is relatively weak. The impact of 5kV will cause about 10% ceramic capacitor failure. When 10kV reaches 60%, the damage rate will reach 60%, while TVS can withstand the voltage of 15kV. In the use of handheld devices, because of frequent contact with the human body, each port must be able to withstand at least the 8kV contact impact (IEC61000-4-2 standard). It is visible that the use of TVS can effectively guarantee the qualified rate of the final product.
TVS and MLV: multi-layer metal oxide structure devices (MLV) can also perform effective instantaneous high pressure shock suppression. Such devices have nonlinear voltage - current (impedance performance) relations, the cut-off voltage can reach 2~3 times the initial suspension voltage, and this characteristic is suitable for protection of circuits and devices that are less sensitive to voltage, such as power supply. Loop. The TVS diode has a better voltage cut-off factor (Figure 2) and also has a lower capacitance, which is very important for the high frequency ports of the handheld device, because the high capacitance will affect the data transmission, cause distortion or degrade. All kinds of surface packages of TVS diodes are suitable for assembly line assembly, and the chip structure is easy to integrate other functions.
Characteristics of TVS diode
There are many ESD protection devices for portable devices, for example, designers can use discrete devices to build protection circuits, but this method has gradually been replaced by more integrated devices due to the limited space and avoidance of loop self inductance of portable devices. Multi-layer metal oxide devices, ceramic capacitors and diodes can all be effectively protected. Their characteristics and performance are different. The unique performance of TVS diodes in such applications has won more and more market.
The most significant feature of the TVS diode is the rapid reaction, which makes the instantaneous pulse effectively curbed before the damage to the circuit or device. Two is the lower cut-off voltage, which is more suitable for the battery powered low voltage loop environment. In addition, the improvement of the TVS diode design makes it lower leakage current and junction capacitance, so it has more ideal performance in handling the electrostatic shock of the high-speed transmission circuit.
Another feature that can not be ignored is that diodes can be easily integrated with other devices on a single chip. There are many existing devices that integrate the functions of EMI filtering and RFI protection with TVS, which not only reduces the cost of the number of devices used in the design, but also avoids the associated self inductance of the wiring on the PCB board.
The use of TVS diode to implement ESD protection for portable equipment is a convenient, effective and reliable way. It is the key to successfully apply the parameters and integration degree according to the specific use. In addition, the optimized PCB design is also essential.
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