What are key considerations for USB Type-C ESD protection?

They include protecting its numerous signal pins using TVS or Zener diodes placed close to the port, selecting diodes with appropriate working voltage to withstand high-power charging, and ensuring the protection devices have suitable capacitance to maintain high-speed data integrity and voltage and transient ratings that meet various IEC 61000-4 standards.

High-voltage static electricity can be especially damaging in USB Type-C applications. It can occur when a user touches a port or a charged cable is connected. The ESD protection challenges are exacerbated by the tightly packed pins of the Type-C connector, designed for small devices, that significantly increase the risk of short circuits during ESD events or from debris or moisture.

Figure 1. USB-C packs a variety of functions with widely varying ESD protection needs in a small connector. (Image: Semtech)

Specific protection needs

ESD protection can be especially challenging for the low-voltage data pins that are close to the power-delivery pins. Robust ESD protection is needed to support reliability and prevent costly damage. In the case of power pins, thermal sensing is also an important consideration.

Comprehensive protection solutions must address ESD using TVS and Zener diodes in addition to temperature sensing on the VBUS. The variety of data buses and speeds can make it difficult to simultaneously manage layout, package size, and capacitance needs to minimize signal degradation and ensure the necessary level of protection (Table 1).

Table 1. Example of ESD protection categories for USB Type-C functions. (Table: Wevolver)

Type-C cables can deliver up to 100 W, creating new safety and reliability concerns. That’s particularly true if a short circuit occurs due to the entry of moisture, dust, or other contaminants. Temperature indicators are available to monitor the VBUS connector. They feature a switching temperature of +100 °C with zero IR loss, and their 2.0 x 1.2 mm footprint makes it easy to integrate into compact designs.
The USB 2.0 lines, D+ / D-, are the differential data lines that run up to 480 Mbps for USB 2.0, ensuring backward compatibility. These data lines need moderately fast ESD protection and low, but not the lowest, capacitance. In this case, designers can turn to devices like unidirectional TVS diodes rated 0.3 pF and meet the requirements of IEC 61000-4-2, ±22kV contact, ±22kV air for ESD, IEC 61000-4-4, 40 A electrical fast transient (EFT) burst (tP=5/50ns), and IEC 61000-4-5, 2.5 A lightning (tP=8/20μs).
The Transmit/Receive (TX / RX) pins are the differential pairs used for SuperSpeed data transfer (USB 3.x and USB4) with data rates up to 40 Gbps. Very low capacitance is needed to ensure adequate protection without impacting data transmissions. That’s possible with 0.09 pF 12 kV bidirectional discrete TVS diode arrays that conform with IEC 61000-4-2, ±12kV contact, ±12kV air for ESD, IEC 61000-4-4, 40 A electrical fast transient (EFT) burst (tP=5/50ns), and IEC 61000-4-5, 2.0 A lightning (tP=8/20μs).
Configuration channels (CC1 and CC2) and the sidebands (SBU1 and SBU2) are used for alternate connection modes like DisplayPort or HDMI and allow attached devices to set their role (host or peripheral), negotiate power requirements, and establish connection details. A higher capacitance device is suitable since the data rate is slower. In this case, Zener diodes with a low leakage current of 0.5 μA and a capacitance of 25 pF can supply the needed protection. Zeners are available that comply with IEC610000-4-2, ±30kV contact, ±30kV air ESD, IEC610000-4-4, 40A (5/50ns) EFT, and IEC 61000-4-5 5A (8/20μs) lightning.
The power delivery (PD) system includes the voltage bus (VBUS) and ground (GND) pins. PD is specified to deliver up to 20 V by default, but can negotiate voltages up to 48 V when needed. Since these pins deliver DC voltages, capacitance is not a significant issue, and unidirectional TVS diodes rated for 200 W and 60 pF are suitable. They’re also available rated for IEC 61000-4-2, ±30kV contact, ±30kV air, ESD, IEC 61000-4-4, 40A (5/50ns) EFT, and IEC 61000-4-5 8A (8/20μs) lightning.

Summary

Robust and compact ESD protection is key to delivering successful USB Type-C solutions. It can be challenging to implement due to the wide range of voltages and data rates on the various pins and the crowded size of the connector. Fortunately, designers have a wide selection of TVS and Zener diodes plus thermal monitors to deploy.