Although the Type-C interface is powerful, it still needs to be protected

    Although USB Type-C is powerful, the issue of product reliability cannot be ignored. The risks caused by hot swapping, short circuits, ESD, faulty devices, and user misoperation during use require reliable circuit protection measures to resolve. In addition, although D+/D - is not directly adjacent to VBUS, there is a possibility of short circuits, but the probability is lower compared to CC and SBU, so D+/D - also requires overvoltage protection. In addition to overvoltage protection, the above pins also require IEC 61000-4-2 system level ESD protection.

    Recently, Google launched the Android 10 operating system for all four generation Pixel smartphones. XDA developers unexpectedly discovered through the source code of Android 10 that this operating system version has new features for USB port contamination and overheating detection. These two new features not only protect the reliability of data transmission, but also ensure the safety of USB port charging, which is quite practical.

    With the acceleration of the commercial process of USB Type-C, its powerful functions are gradually becoming prominent. While enjoying the powerful functionality of USB Type-C, the market is gradually increasing demand for protection solutions that balance its reliability and security. Aiwei has also launched its own Type-C interface protection scheme. Place the overvoltage protection chip (OVP) in series on the pin circuit. When a voltage above the OVP threshold is detected on these lines, the internal high-voltage power switch is disconnected and the rest of the system is isolated from the high-voltage state present on the connector.

    The overvoltage protection scheme for CC and SBU channels is similar, but there are differences in channel functions that need to be addressed separately.

    The SBU channel is designed to be compatible with the D+/D-channel of USB2.0, with a bandwidth of over 800MHz, which requires reducing parasitic capacitance on the channel. The parasitic capacitance on the channel mainly comes from the ESD tube and switch tube for electrostatic protection. The small capacitance ESD designed by Ai Wei effectively reduces the parasitic capacitance on the SBU channel, which is the key to increasing the bandwidth of the SBU channel. At the same time, the switch channel routing and PAD layout have been optimized to further reduce parasitic capacitance.

    Due to short circuits, hot swapping, or device failures, it is possible to cause surges. So each pin of the Type-C interface needs to have TVS protection, either built-in or external. The built-in TVS can eliminate external patch TVS, save PCB board area, and reduce the difficulty for customers to choose high-voltage TVS. TVS tubes can release surge energy, reduce surge voltage, and effectively protect downstream circuits.

    The starting voltage of TVS must be greater than the DC working voltage of OVP power switch tube, and the embedded voltage of discharge surge must be less than the breakdown voltage of switch tube; The size of the surge tube is large enough to release energy without thermal damage.

    The principle of surge protection is that when a surge occurs at the interface, the surge voltage is greater than the starting voltage of the surge tube. The TVS tube begins to release energy, and the voltage at the interface end is embedded. The greater the released energy, the greater the voltage drop caused by parasitic resistance in the current path. The embedded voltage is also raised, and the embedded voltage cannot be greater than the breakdown voltage of the OVP switch. When a surge occurs, overvoltage also occurs at the interface end. At this time, the OVP switch tube is disconnected to protect the downstream circuit from damage. The faster the OVP switch tube overvoltage is disconnected, the lower the residual voltage output by the OVP switch tube, and the better it can protect the downstream circuit.