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The major electrical parameters and selection techniques of TVS2020/06/08

Living in a technological era, there are so many electronic products in our lives, electronic products such as smart phones, satellite navigation system, digital TV has become part of modern life. Due to frequent contact with the outside world, these electronic products are susceptible to damage caused by electrostatic discharge (ESD). Because electrostatic discharge is everywhere, more and more international companies to maintain product stability and brand value, they will request their products to meet the ESD immunity requirements of IEC 61000-4-2, make sure that their product will not be affected by ESD.
 
In consumer electronics, we need to pay particular attention to ESD problem in high speed signal interface, power supply, screen and headphone jack, these places which are frequently touched. In these vulnerable areas, according to different product characteristics, we can add different electrostatic protection element to increase immunity to the ESD of these weak points. As long as these vulnerable areas is properly protected, the reliability of electronic products can be increased significantly. In the history of the electrostatic protection element, Zener diode, varistor, gas tube, silicon controlled rectifier (SCR), have been used for a long period of time, but nowadays consumer electronics function is more powerful, USB3.0, HDMI high speed transmission interface is everywhere, these electrostatic protection element are outdated to the advanced portable electronic products. For example, the drawback of zener and varistor is the size and capacitance values are huge, it's not easy to place it in portable electronic products. Although the gas tube itself has a strong immunity to ESD, but it's trigger voltage is too big, the electrostatic discharge will destroy the internal circuit before the gas tube turn on. Not only the high trigger voltage, the another problem of SCR is the low holding voltage, the lower holding voltage will cause latch-up issue causing damage to the internal circuit when the ESD bombardment is over. Summarize these shortcomings, with the past experience in electrostatic protection works, AMAZING Microelectronic Corp. (AMC) has proposed the new type of electrostatic protective element so called Transient Voltage Suppressor (TVS), The TVS developed by AMC is a semiconductor device, the capacitance is ultra low, and the turn-on speed is very fast, based on different applied voltage, we provide a enough correspond holding voltage so that the system is latch-up free. Depending on the end application, we also offer the different package size. Fig. 1 is an example of using the TVS to protect the power supply terminal, when there's a ESD pulse occurs in the power supply terminal, without TVS, the ESD pulse will destroy the internal circuit directly, the system will out of work at severe cases. But if we have put the TVS in the power supply terminal, when the ESD pulse occurs, the ESD pulse will be effectively suppressed to a lower voltage "Vclamp". Customers need to deal with the problem of electrostatic discharge, whether in order to stabilize the product or to get a good brand image, just follow a few general direction below, and you can be very easy to choose a suitable TVS provided by AMC, increase the ability of the product to resist ESD bombardment, significantly improved the stability of the product.
 
Fig. 1 Power system protection by TVS
Fig. 1 Power system protection by TVS 
 

On our AMC official website, customers can see the page like Fig. 2 , those indices you see on the page is the most important reference data, and we can make choices in accordance with the following steps:
 
 1. Package style: we provide different package options for different end product such as smart phones or laptops, for the smart phone product, light and the thickness is the most important thing, so the size of TVS must be small enough, especially the thickness of the package must be thin enough. For single-channel protection, we can choose the package sizes such as 0402 (1.0mm x 0.6mm x 0.45mm) or 0201 (0.6mm x 0.3mm x 0.3mm), this type of product can be found in the AZ5-series. But if the end product is laptop case, instead, we recommend using the array package, not only reducing the PCB layout area, TVS arrays can protect multiple set of signal lines at the same time, so the average cost of each signal line will be lower, This type of product can be found in AZ1-series or AZC-series.
 
 
Fig. 2 Some important parameters in selecting TVS device
Fig. 2 Some important parameters in selecting TVS device
 
 
2. In high-speed signals ESD protection, since TVS device is used in parallel to high-speed signal on the PCB, therefore, the most important index to note is the parasitic capacitance (Cin), avoiding excessive parasitic capacitance causing the attenuation of high-speed signals. In addition to reference the parasitic capacitance of TVS, some users will do the Eye diagram measurement, ensure the high-speed signals are not distortion or affected by the capacitance of TVS. A HDMI 2.0 corresponding eye diagram measurement is shown in Fig. 3. We will get an eye-shaped waveform by way of signal superposition, the interference to the signal is less when the opening of the eye diagram is larger. For use in high-speed signals TVS device, the eye diagram should be same as Fig. 4, after putting the TVS on system, the amplitude and the width of eye diagram should not be change. In particular, some signal line trace of the high-speed differential signal should also be very careful consideration, to avoid unnecessary traces and turning otherwise the high-speed signal will be disturbed, AMC specially designed the low-capacitance TVS with a special Dual Flat No-Lead (DFN) package, when user layout the high-speed signals configuration, the trace can direct feed-through the TVS device like Fig. 5, without extra trace and no need to re-verify the resistance value of PCB, solving ESD problem is become more easier.
 
 
Fig. 3 HDMI 2.0 eye diagram measurement without TVS
Fig. 3 HDMI 2.0 eye diagram measurement without TVS
 

Fig. 4 HDMI 2.0 eye diagram measurement with AZ1043-04F

Fig. 4 HDMI 2.0 eye diagram measurement with AZ1043-04F

 

 

3. According to product demand to choose polarity and operation voltage of TVS device. TVS device should work in standby state when the electronic product in normal operation, usually we promised TVS leakage current less than one microampere in standby state, or the electronic products will have excessive power consumption. Choosing the correct operating voltage of TVS is important, wrong operating voltage not only causes excessive power consumption, severe cases may even destroy electronic products. As TVS polarity, if we want to solve the ESD problem of mobile antenna, since the mobile antenna signal more than 10V, but sometime it down to less than 0V, so we must choose the appropriate voltage and bi-direction TVS like AZ4-series. But if we want to solve the ESD problem of USB2.0, the maximum voltage is typically less than 5V and the lowest voltage is larger than 0V, so this time, 5V uni-direction of TVS like AZC099-04S is a good choice.

 

 

Fig. 5 TVS with DFN package let the signal traces easier.

Fig. 5 TVS with DFN package let the signal traces easier.

 

4. TVS device itself must have enough immunity to ESD, when ESD is coming, TVS itself cannot be damaged and then out of function, a basic requirement to TVS is be able to withstand ESD of IEC 61000-4-2, Level 4 (±15kV air, ±8kV contact discharge), and the characteristic of this TVS device would not be changed by the times ESD bombardment. Another thing we concerned is current to voltage characteristics of TVS during the electrostatic bombardment, we can get the current to voltage characteristics of TVS like Fig. 6, through the Transmission Line Pulsing system (TLP), this current to voltage characteristics determines the protected internal circuit, will encounter how many voltage across itself when subjected to ESD bombardment, if the clamping voltage is larger, then the risk of internal circuit damage is higher. From Fig. 6, if we choose AZ1043-04F as ESD protection device, when the system encounters 8kV of electrostatic bombardment, the cross voltage is about 10V of protected internal circuit, as long as the breakdown voltage of internal circuit is higher than 10V, AZ1043-04F can protect the whole system from damage. The current to voltage characteristics of TVS is important, we can get the information like clamping voltage or turn on resistance, to predict whether the protection can reach the design requirement, the other secrets that hidden in TLP measurement characteristics will be described in more detail in later chapter.

 

 

Fig. 6 TLP measurement of AZ1043-04F

Fig. 6 TLP measurement of AZ1043-04F

 

 

ESD problems are not so serious in past years, but in the past decades, the gate length and gate oxide thickness of semiconductor has been shrunk from micrometer to nanometer, the immunity to ESD of semiconductor is getting worse, consumer electronic device is very easy to be affected by electrostatic discharge, when the impact is not severe, we can just reboot the system and solving the problem. But if the energy of ESD is huge, unfortunately the immunity to ESD of internal circuit is not enough, circuit may be seriously damaged and need to return to the original company to make the repair or replacement action. When consumer choosing electronic product, not only the product price and performance, quality and availability of product is also very important factor, if consumers need routine maintenance after purchasing the product, then the product will soon be abandoned by consumers, when dissatisfied consumers more and more, this bad experience has been spread out, brand impression in the eyes of customers will be bad. AMC hope to solve ESD problem from the perspective of circuit design, according to several points of the second chapter, we can choose the most suitable TVS to product even predict the magnitude of improvement. The TVS provided by AMC is inexpensive, adding some TVS device in those vulnerable areas will not increase the total cost too much, but it can significantly increase the reliability of the product, reduce logistics costs and manpower requirements from the product replacement. Therefore, to those companies who pursue the company's growth, hoping to bring customers a better experience, we strongly recommend incorporate TVS to product layout.

 

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