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TVS Protection Solution against Interface Failure due to VBUS Accidentally in Contact with CC and SBU


USB-IF launched the Type-C standard in 2013. This transmission interface became an instant hot topic among consumers and in the industry as soon as it was launched. Type-C not only features compact size and insertion in either orientation, but also acts as an interface for both signal transmission and power supply. The PD 3.0 protocol supported by most mainstream equipment is capable of up to 20V and 5A. For signal transmission, Type-C is capable of up to USB4 40Gbps, and completely compatible with A/V transmission protocols, such as DP. 

Type-C has a lot more than the eyes can see. It is as small as 8.6mm*2.6mm, supports insertion in either orientation, and has a wide range of functions. However, there are Ying and Yang for everything. In such a compact space, there are 24 pins crammed in the connected. The spacing between the pins is very little. In a real-life complex application scenario, accidental connection, or misalignment between pins it not unheard of. One of the most dangerous situations is VBUS accidentally in contact with CC or SBU pin during normal supply of DC power at 20V, as shown in Fig. 1. Normally, the operating voltage is 5V for CC and SBU. When there is an accidental injection of 20V DC Power, it is likely to cause burned rear-end ICs and interface TVS damage. That’s why it is necessary to consider not to cause system collapse if VBUS makes accidental contact with CC and SBU, in addition to satisfying ESD and EOS protection in interface protection design. 

Figure 1. Pin locations in a Type-C interface

Facing such a failure mode reported from end customers, consumer product manufacturers started asking for DC current withstanding test for CC and SBU interfaces in addition to the existing ESD test; that is, DC current withstanding test lasting 1 to 3 minutes is required for 20V DC Power. The mainstream design architecture is to add a TVS close to the Type-C interface, and a USB control chip with OVP (Over voltage protection) is added at the rear end. A design architecture like this is enough to guarantee sufficient protection. However, the use of a TVS featuring VRWM=5V will not pass the DC current withstanding test. It needs a TVA with VRWM≥20V to do the job. Having said that, this brings up another problem. For a TVS with VRWM≥20V, the clamping voltage, VCL, is inevitably high, which leads to less than satisfactory ESD/EOS protection, or even failure of the entire unit in ESD Pin injection test. For this, a TVS solution that not only passes the DC current withstanding test, but also provides good protection is needed, and Amazing Microelectronic provides just that, in the package of AZ5H25-01B. 

Unlikely 5V TVSs, AZ5H25-01B is unique because its VBV (reverse breakdown voltage) is no longer 6V. Instead, it ensures that the TVS will not be activated until it is 26.5V, as shown in Table 1. This keeps AZ5H25-01B from accidental activation during the 20V DC test, and prevents the risk of TVS tube getting burned by DC energy. Meanwhile, the ESD clamping voltage of AZ5H25-01B is 10V at 8V, enough to help the entire unit pass ESD test. The surge tolerance is up to 6.5A (8/20μS, IEC61000-4-5). All of the above enables good EOS protection capability. 

Table 1. Electrical parameters of AZ5H25-01B

One of the reasons that AZ5H25-01B has outstanding ESD clamping voltage is that the lowest point of snap-back voltage, Vhold, can be as low as 6V after TVS is activated, as shown in Fig. 2. This not only achieves lower clamping voltage, but also ensures no impact on CC/SBU signals and, thus prevents latch-up. Amazing Microelectronic defines AZ5H25-01B at VRWM=5V. This eliminates the risk of latch-up engineers may encounter when selecting a TVS based on VRWM.

Figure 2. Characteristics curve of AZ5H25-01B TLP

The AZ5H25-01B package size 0201. It is compact, flexible for layout, and capable of satisfying the increasing needs for device miniaturization. For an omni-functional USB4 interface, provides the super-low capacitance TVS AZ5B9S-01F for ultra-high speed signal interfaces; AZ5H25-01B that features CC/SBU that satisfies DC current withstanding test and has an extremely low ESD clamping voltage; and the AZ4520-01F/AZ4920-01F that passes VBUS high-surge test with flying colors. A layouts example is presented in Fig. 3. 

Figure 3. Layout example for AZ5H25-01B Type-C USB4 interface

Type-C interface is seen in more and more devices, and the scenarios where it is used are becoming increasingly complicated as time evolves. What comes with it is the increasing percentage of devices returned for repair. That is why it is necessary to consider not only ESD and EOS protection, but also special circumstances like DC current withstanding tests during system design. Amazing Microelectronics has hundreds of product lines to help customers improve ESD/EOS tolerance, reduce repair rate, and make products more reliable. 

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