Thunderbolt 5 is the latest generation of high-performance data-transfer technology. It combines high-speed data transmission, multifunctional expansion, and powerful power delivery, and is widely used in various high-end electronic devices. As imaging technology continues to improve, the pixel counts of computers, smartphones, and cameras are getting higher, and storage capacities are becoming larger. Users’ demand for data transfer continues to increase, and they also expect faster transfer speeds. The Thunderbolt 5 specification provides bidirectional transmission speeds of 80 Gbit/s, meeting the growing need for higher transfer rates. To achieve such high-speed transmission, Thunderbolt 5 controller ICs must use advanced semiconductor process technologies; however, this also causes the ESD withstand capability of Thunderbolt 5 controller ICs to decline rapidly.
Thunderbolt 5 is built on the USB Type-C physical interface. This interface not only increases the transmission rate to 80 Gbit/s, but also supports fast charging with a maximum power delivery of 240 W. In the future, the USB Type-C interface will become the mainstream connector for all consumer electronics products, including personal computers, laptops, tablets, smartphones, and other devices. Because Thunderbolt 5 is an ultra-high-speed transmission interface and is externally exposed to users for frequent plug-in and unplug operations, the most common usage is plug-and-play and disconnect-on-removal. However, this hot-plugging behavior is also often the root cause of abnormal system operation and even damage to USB Type-C controller components, because transient noise such as electrostatic discharge (ESD) originates from this hot-plugging action. During hot-plugging, since the signal lines at the connector end are already charged, the cable itself is charged and discharges when it contacts the system. This phenomenon is equivalent to an ESD event and can cause serious damage to the system; it is commonly referred to as direct discharge. In current system-level ESD testing, more manufacturers require products to be tested using Direct-Pin Injection to simulate the ESD events encountered at the user end.
In addition to meeting the original IEC 61000-4-2 requirement, some brand customers even specify that the USB Type-C connector in their products must pass an 8 kV ESD strike using Direct-Pin Injection, and the system must pass the test without any influence on operation. Therefore, using ESD protection devices on the USB Type-C interface to prevent ESD events from interfering with data transmission is absolutely necessary. Figure 1 shows the Direct-Pin Injection test setup.
Figure 1: Direct-Pin Injection Test Setup
For high-speed Thunderbolt 5 interfaces, the following factors must be considered when selecting ESD protection devices:
1. To ensure signal integrity during high-speed Thunderbolt 5 transmission, an ESD protection device with low parasitic capacitance should be selected. A parasitic capacitance below 0.2 pF is recommended.
2. The ESD protection device must have high ESD withstand capability. At a minimum, it should withstand IEC 61000-4-2 contact-discharge ESD strikes at 8 kV.
3. ESD clamping voltage is the most important reference parameter. For an ESD protection device to provide effective system protection, the device itself must withstand sufficiently high ESD strikes, and its clamping voltage must also be low enough to clamp ESD energy at a lower voltage and prevent damage to internal system circuits. This clamping voltage is the most important parameter for evaluating the protection effectiveness of an ESD protection device for system circuitry.
4. This interface also supports fast-charging technology and can support voltage levels of 5 V, 9 V, 15 V, 20 V, 28 V, 36 V, and 48 V. Because wired charging can generate frequent ESD/EOS issues on the power line during hot-plugging, a more comprehensive external surge ESD/EOS protection solution must be designed into the system.
Amazing Microelectronic Corp. has advanced ESD protection design technology. To address the protection requirements of Thunderbolt 5, the company has introduced the AZ5BFS-01M ESD protection device. To prevent the parasitic capacitance of the protection device from affecting the high-speed transmission of Thunderbolt 5 differential signals, the parasitic capacitance of AZ5BFS-01M is below 0.2 pF, enabling it to pass the 80 Gbit/s Eye Diagram test. Most importantly, AZ5BFS-01M features an extremely low ESD clamping voltage, which effectively helps the Thunderbolt 5 interface pass an 8 kV ESD strike using Direct-Pin Injection. Figure 2 shows the current-voltage curve measured for AZ5BFS-01M using TLP. Under an IEC 61000-4-2 contact-discharge ESD strike at 8 kV (equivalent TLP current of approximately 16 A), the clamping voltage is only 6.5 V. This can effectively prevent system products from experiencing data errors, crashes, or damage during ESD testing.
Figure 2. ESD Clamping Voltage Characteristic Curve of AZ5BFS-01M
As electronic products continue to develop toward thinner, lighter, smaller, and more compact form factors, the printed circuit boards (PCBs) inside products are also becoming smaller. At the same time, as product functionality becomes more powerful, routing becomes more complex. PCB area has therefore become extremely valuable, creating considerable challenges during product design. AZ5BFS-01M uses an ultra-small MCSP0603P2YS package, with a size of only 0.6 mm x 0.3 mm and a height of only 0.25 mm. It mainly protects the four differential pairs (TX and RX) of Thunderbolt 5. In addition, only one AZ1045-08F is required to protect the remaining signal lines (D+/D-/CC/SBU). In particular, AZ1045-08F uses a staggered pin arrangement to support a feed-through PCB layout design, eliminating many routing difficulties. This not only helps shorten the PCB layout effort during the product design phase, but also reduces PCB area and lowers system cost. This interface also supports fast charging, so one ESD protection device should be selected for the power rail. Depending on the designed voltage, a suitable ESD device (AZ3105-01F/AZ4510-01F/AZ4516-01F/AZ4520-01F/AZ4528-01F/AZ4536-01F/AZ4548-01F) can be selected for protection. With this arrangement, the entire interface can be fully protected from ESD/EOS threats. Figure 3 shows the complete ESD/EOS solution protection circuit for the Thunderbolt 5 interface.
Figure 3. Thunderbolt 5 Interface ESD/EOS Solution Protection Circuit