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EOS Protection for External Interface of New Generation Laptops


Laptop computer has become an indispensible part of people’s work, entertainment and even daily life. The needs for mobile office, online meeting and home entertainment skyrockets with the current global pandemic. With the increasingly complicated application scenarios come the challenges for the laptop reliability. Today, the percentage of laptops returning for servicing is still alarmingly high despite the maturing electrostatic testing and protection solution. A certain percentage of the products are returned for repair and most of these repairs are required due to EOS.

EOS stands for Electrical Over Stress. It is an extensive idea where an electric element is subjected to excessive voltage / current. The EOS referred to in this article is the lightning / surge energy according to IEC61000-4-5. The test waveforms used in today’s consumer products are 1.2/50μs open-circuit voltage and 8/20μs short-circuit current, as shown in Fig. 1, and the network impedance used is 2Ω.

Figure 1: 1.2/50μs open-circuit voltage waveform (L) and 8/20μS short-circuit current waveform (R)

EOS lasts longer than ESD and packs far more energy as well. That’s why we need to consider more about the maximum dissipative current (Ipp) in TVS tube during the evaluation of TVS’s EOS protection. This parameter is used to describe how well the TVS tube itself tolerates EOS. The greater the Ipp is, the more capable it is of surge energy tolerance. In a system application, not only TVS tolerance, but also TVS protection has to be considered. The key parameter is the surge clamping voltage (Vcl-surge), where the lower the Vclis, the greater the protection can be. 

The application of Type-C on laptops is experiencing an explosive growth, as there is at least a Type-C interface on every new product available in the market. Type-C can be used as a power interface thanks to its support for the PD protocol, and this takes the user experience to a new level. However, it does come at the cost of challenges never having been encountered in product designs. The Vbus on the power cable may be subjected to extreme EOS energy impact, which includes, but not limited to, plugging and unplugging the cable and poor connector contact. Such energy may burn the PD control chip and the computer is dead. That’s why high TVS tolerance and robust protection are both needed. Amazing Microelectronic launched the AZ4920-01F that features Ipp up to 140A with Vcl=26V@40A, more than enough to protect the vulnerable PD control chip. In addition, the DFN2018P6E packaging that is widely used in the industry is introduced to AZ4920-01F, which is a great choice from the supply perspective. That being said, this packaging technique requires a relatively large footprint on PCB. Now, Amazing Microelectronic just rolled out the AZ4520-01F with smaller DFN1610 (0603) packaging, and products with smaller packaging but better performance are on the way. 

Figure 2: Type-C Vbus EOS test setup

Not only Type-C has the issue of EOS on Vbus, but the data interface may be subjected to the impact of surge energy. Usually, the D+/D- of USB 2.0 is connected directly to CPU; once CUP is burned, the cost to repair can be sky-high. CC and SBU port are also vulnerable to EOS. As shown in Figure 2, major manufacturers started running EOS testing. With the consideration of parasitic capacitance for data ports in mind, Amazing Microelectronic’s AZ5515-02F features a parasitic capacitance of 0.8pF (typ.) and an Ipp of 11A, and the clamping voltage is merely 9V at 11A. This gives TVS a greater fighting power against negative voltage surge energy, as the clamping voltage is only -3V with starting voltage at approximately -0.7V and surge current at -11A. That’s great news for protection of ICs that are sensitive to negative voltage. AZ5515-02F comes with DFN1006P3X packaging (0402-2ch). It provides protection for 2 channels at the same time, which solves the issue with limited prime real estate on PCB. Figure 3 shows the surge protection curves of AZ5515-02F

Figure 3: EOS protection curves of AZ5515-02F


The EOS protection for Type-C’s high-speed differential interface TX/RX is another issue that gets the attention of the industry. The signal rate demands extremely low TVS capacitance, and both tolerance and protection are required at the same time. Therefore, AZ5B0S-01F is a perfect choice when evaluating a protection solution, since this TVS features a parasitic capacitance as low as 0.2pF (typ.) and IPP up to 7A with Vcl=4V@7A, and it supports up to USB4 rate which is outstanding protection for ICs at the rear end. The packaging is DFN0603 (0201). Figure 4 shows the complete Type-C port protection design. 

Figure 4: USB4-supporting Type-C EOS protection scheme


Another issue for which laptops are returned for EOS repair is the HDMI port. The sink end is usually live, meaning that the frequent plugging and unplugging easily leads to EOS and, therefore, that TVS with robust surge protection is required. Amazing Microelectronic’s AZ1243-04F provides extreme tolerance up to IPP=12A for HDMI2.0 interface with Vcl=7.5V@12A. With industrial advancing, HDMI2.0 is experiencing a transition to HDMI2.1, data transmission rate is increasing from 16Gbps to 48Gbps, and the rear-end ICs become more sensitive, resulting in greater demands for clamping voltage and parasitic capacitance in TVS. Amazing Microelectronic’s AZ1123-04F features a parasitic capacitance < 0.2pF and IPP up to 6.5A, provides greater protection with Vcl=10V@6.5A and support for HDMI2.1. For the low-speed HDMI interface, we have integrated AZ1575-04S for powerful EOS protection. The IPP reaches up to 70A for power port and 20A for IO port. Figure 5 shows the complete EOS protection scheme for HDMI interface.  

Figure 5: HDMI 2.0/2.1 EOS protection scheme

As clients come up with a wide variety of demands and the development of PC industry is still accelerating, more and more major manufacturers not only run EOS tests on more interfaces, but also impose more rigorous requirements for test levels. Amazing Microelectronics has top-notch solutions and rich experience to address customers’ issues quickly and accurately. 

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