The present market greatly emphasizes the stability of electronic products during use. Hence, the electrostatic discharge (ESD) waveform has become one of the items that must be tested by hardware developers when designing products. However, in recent years, developers have also considered testing another more destructive EOS (Electrical Over Stress) waveform. The EOS simulation waveform of IEC 61000-4-5, the most commonly applied, is a microsecond (µs) duration and it is used to simulate overvoltage surges such as lightning coupling, power on/off switching, hot swapping etc.
Why do hardware developers place importance on this simulation waveform? Some following actual cases are to be shared to understand why after investigating customers ‘returned merchandise, the R&D engineers decided to add an EOS test item to improve product stability.
(1) A well-known TV manufacturer has incorporated ESD protection components to the models sold in the domestic and international markets. However, they found that the return rates among the models sold in South America and Southeast Asia were relatively high. Analysis results pointed out that the reason was EOS damage. After sending personnel to conduct an on-site investigation, they learned that local consumers were accustomed to moving their TVs outdoors to watch with their neighbors, causing lightning couplings that were previously only encountered outdoors or with long-distance wiring to get into the product and cause damage to the product. Therefore, they finally concluded that the use of TVs in these areas are different from other regions, so EOS testing is included to TV models sold in these regions.
(2) Some consumers discovered that sparking occurred when connecting the TV to the set-top box, and often caused malfunctions after the sparking. Therefore, the manufacturer sent personnel to investigate. Investigators previously speculated that the damage was caused by a CDE (Cable Discharge Event) similar to electrostatic discharge. After investigation, it was found that the cause of the sparking was that the two-hole plug of the TV was not grounded, causing the reference levels of the ground wires of the two devices to be different from the same reference level. A pressure differential surge occurs after connecting these devices. The manufacturer successfully reproduced similar phenomena in damaged ICs through EOS waveform simulation experiments, and subsequently added EOS-related protection.
(3) A tablet device is to be sold to continental dry environments such as North America and Canada. Therefore, the hardware R&D personnel have upgraded the ESD Level of the product to Contact ±20kV, but they still receive several returned products with similar damage every year. The manufacturer conducted various experiments through ESD waveforms but was unable to reproduce the customer returned damage phenomenon. The R&D engineers were at their wits’ end to this problem, so they approached AMAZING Microelectronic Corp for an improvement solution. During the discussion, we learned that the customer will hot swap the tablet from the connection port, so we judged that EOS may cause this situation, so we used the EOS waveform to conduct simulation experiments in the AMAZING Microelectronic Corp Laboratory, and we finally confirmed the simulation experiment results are consistent with the damage caused by market repairs after Decap. Therefore, we recommend that they use protective components with EOS protection effects when updating versions to reduce the chance of customer returns.
(4) The last but not the least more interesting case is from the surveillance system. In this case, the outdoor camera is connected to the indoor NVR network port (RJ-45) through a network cable. This network port has considered the outdoor wiring, so the manufacturer has a complete EOS design solution for this use case. However, when the lightning coupling energy enters the system through the RJ-45, the NVR itself is not damaged. On the contrary, the monitor system screen connected via HDMI and the control device connected via USB were damaged. The same situation may also occur in set-top box products whose signal input is a coaxial cable. If EOS protection is not considered, energy may enter the product through the coaxial cable and damage the set-top box and peripheral products connected by I/O interface. This incident also shows that there are more potential EOS situations that cannot be detected at the beginning of product design.
As mentioned above, the energy of EOS is much greater than that of ESD. The original ESD protection components alone cannot withstand such a high-energy surge test. Therefore, it is particularly necessary to add protection components that can effectively withstand and clamp the EOS voltage.
When selecting protection components, hardware developers will configure appropriate protection components such as low clamping voltage, appropriate starting voltage, high tolerance, multi-channel or small package, and even multi-voltage hybrid requirements based on product positioning, size, application scenarios and their own experience. It is a multi-voltage hybrid requirement. With a number of independent research and development patents and long-term cooperation experience with customers, AMAZING Microelectronic Corp has developed products that can meet the many needs of customers, and has designed protection components with EOS protection capabilities for many common I/O ports. The products are all designed using the original ESD protection component packaging, allowing customers to directly upgrade without changing the Pad Layout. For example, the common packaging for high-speed communication interfaces is DFN2510 (2.5mm x 1.0mm), and AMAZING Microelectronic Corp provides ESD protection components and protection components with enhanced EOS capabilities to meet customers' flexible selection needs.
Relatively speaking, knowledge related to ESD design has been developed for many years, and engineers are more familiar with ESD protection solutions. However, EOS is a potential risk that is easily overlooked. It may not occur in familiar environments, but it occurs frequently in other application scenarios. Product damage affects consumer experience and damages merchant reputation. Therefore, professional and targeted protection measures must be formulated. By adding TVS components, EOS specifications can be effectively improved, customer return rates can be reduced, and product value and user experience can be preserved, thereby achieving a win-win outcome.
