ESD protection design for USB 2.0 high-speed ports

Universal Serial Bus (USB) high-speed data applications are also very common, and users may cause ESD events when hot plugging any USB peripherals. In addition, air discharge may occur a few inches away from the conductive surface, which may damage the USB interface and chip. Therefore, designers must provide ESD protection for USB components.

The industry has developed a number of ESD standards for different transient interferences, such as the IEC61000-4-2 international standard for system-level ESD events. In addition, there are some component-level ESD sensitivity test standards, such as the human body model (HBM) and machine model (MM). Semiconductor ESD protection components for USB 2.0 high-speed data line applications should have the following important characteristics:

Very low capacitance : minimizes signal degradation in USB 2.0 high-speed data lines (480 Mbps);

Fast action response time (nanosecond level): protects USB components when ESD pulse signals rise rapidly;

Low leakage current: Minimizes power consumption under rated operating conditions;

Robustness: Able to withstand many ESD events without damage;

Small package: integrated smaller package

This article introduces the key features of ON Semiconductor's new low-capacitance transient voltage suppressor (TVS) diode array, the NUP4114UPXV6, and discusses how to provide effective ESD protection for USB 2.0 high-speed data lines.

Features and configuration options of NUP4114UPXV6

NUP4114UPXV6 is a TVS diode array that is very suitable for ESD protection of USB 2.0 high-speed data lines. The device has an extremely low capacitance of 0.8pF (typical capacitance between I/O lines and ground), which can minimize signal attenuation in USB 2.0 high-speed data lines. The device meets the system-level IEC61000-4-2 standard for 13 kV contact discharge, and can withstand CMOS device-level ESD rated pulses of human body model Class 3B (over 8 kV) and machine model Class C (over 400V), with strong ESD protection performance. In addition, it uses a SOT563 package with a size of only 1.6×1.6×0.55mm, which is very suitable for ESD protection of USB2.0 high-speed data lines and other high-speed applications in applications such as computers, mobile phones , and MP3 players.

The NUP4114UPXV6 can protect up to 4 data lines, driving transient overvoltages to a clamping reference point, protecting the application from transient overvoltage conditions. Whenever the voltage on the protected line exceeds the reference voltage (Vf or VCC+Vf), the steering diodes in the device will be forward biased. These diodes force the transient current to bypass the sensitive CMOS chip instead of passing through it.

In protection applications, the data lines are connected to pins 1, 3, 4, and 6 of the device. The negative reference is connected to pin 2, and this pin must be connected directly to ground through a ground plane to minimize the ground inductance of the printed circuit board (PCB). It is also important to keep the trace length as short as possible to minimize parasitic inductance.

The NUP4114UPXV6 has three configuration options. Configuration option 1 uses VCC as the reference and protects four lines plus the power supply (Figure 1). In this configuration, pin 5 is directly connected to the positive power supply input (VCC) and the data lines are referenced to the supply voltage. Internal TVS diodes protect against overvoltage on the power supply input. Biasing the steering diodes reduces their capacitance.

Configuration option 2 uses bias and power isolation resistors to protect the four data lines. The device can be isolated from the power supply by connecting a 10kΩ resistor in series between pin 5 and VCC . This will maintain bias on the internal TVS and steering diodes and reduce their capacitance.

Configuration option 3 uses the internal TVS diode as a reference to protect the four data lines. In applications where a positive supply reference is lacking, or where a fully isolated power supply is required, the internal TVS can be used as a reference. In these applications, pin 5 is not connected. With this configuration, the steering diode conducts whenever the voltage on the protected line exceeds the TVS operating voltage plus a diode drop (VC = Vf + VTVS).

Protecting USB 2.0 High-Speed ​​Data Applications with the NUP4114UPXV6

The USB port consists of 4 lines, of which D+ and D- are used for bidirectional data transmission, and the remaining 2 lines are used for bus voltage and grounding. Figure 2 is a circuit diagram of NUP4114UPXV6 providing ESD protection for USB2.0 high-speed data applications .

USB controller ​

If an ESD transient event occurs, the steering diode in the device diverts the transient current away from the protected IC, while the integrated TVS device diverts the surge current to ground. The TVS component also suppresses ESD events on the voltage bus (VBUS). In these ways, the NUP4114UPXV6 protects sensitive ICs in USB 2.0 high-speed data line applications.

Other USB 2.0 High-Speed ​​Application ESD Protection Solutions

NUP4114UPXV6 is an integrated solution for protecting two USB 2.0 high-speed data lines. The USB 2.0 application shown in Figure 2 does not have an identification (ID) line. In addition to NUP4114UPXV6, this type of USB 2.0 application without an ID line can also use another integrated solution from ON Semiconductor, NUP2114. In addition, different discrete solutions can also be used in this type of application, such as two ON Semiconductor ESD9Ls and one ESD9X, or one ESD7L and one ESD9X, or one of the latest ESD11L and one ESD9X.

In addition, in USB 2.0 applications with ID lines (see Figure 3a), ON Semiconductor's discrete or integrated ESD protection solutions can also be used. For example, three ESD9Ls and one ESD9X can be used as a discrete ESD protection solution, or a single NUP3115UP or NUP4114UP can be used as an integrated solution, as shown in Figure 3.

Conclusion

USB 2.0 high-speed data line applications with rates up to 480Mbps require effective ESD protection. ON Semiconductor's low-capacitance TVS diode array NUP4114UPXV6 provides an extremely low capacitance of 0.8pF, which can reduce signal attenuation in high-speed applications to a very low level. It offers 3 different configuration options to protect up to 4 data lines, protect applications from transient overvoltages, and force transient currents to avoid flowing through sensitive CMOS chips. In addition, the device complies with the IEC61000-4-2 standard and HBM and MM test standards. Therefore, designers can use this device to provide effective ESD protection for USB 2.0 high-speed applications.