Advancing VBUS Protection for 48V USB Power Delivery with SurgeSwitch® Technology

The USB Type-C connector has become the universal interface of modern electronics. From laptops and smartphones to Artificial Intelligence (AI) computing platforms and industrial edge devices, USB Type-C supports both high-speed data transfer and high-wattage power delivery through a single cable. With the adoption of USB Power Delivery (USB PD) 3.1 and its Extended Power Range (EPR), (Table 1) VBUS line voltages have scaled from the familiar 20V/100W standard power range to 28V, 36V and 48V — enabling power delivery of up to 240W over a USB-C cable.

This evolution brings significant design challenges. Higher VBUS voltages introduce higher clamping voltage requirements for transient protection, and conventional transient voltage suppression (TVS) diode solutions designed for this voltage level have high clamping voltages that force designers to specify downstream components with elevated voltage ratings. Semtech's SurgeSwitch^® technology addresses this gap, and the new TDS5311P is purpose-built for 48V VBUS protection in USB PD 3.1 EPR systems.

Table 1: USB-PD Specifications

The Growing Threat on the VBUS Line

The VBUS pin in the USB Type-C connector carries the supply voltage to downstream devices being powered. This pin is also exposed to electrical overstress events, including electrostatic discharge (ESD), electrical fast transients (EFT), cable discharge events (CDE), and surge transients caused by lightning or power distribution switching.

These threats are not hypothetical. A single unprotected ESD event at the VBUS pin — caused by a charged user handling the connector — can damage or destroy downstream power management integrated circuits (ICs) and charging circuits. Surge events, which carry far greater energy, can produce destructive overvoltages across the entire input stage. No user wants to experience a damaged high-end computer due to an ESD or surge event. As USB PD EPR devices increasingly find their way into industrial and high-performance computing environments, the likelihood and severity of these threats grow accordingly.

Figure 1: Protecting the VBUS pin with a SurgeSwitch

Why Clamping Voltage Is the Critical Parameter

When a transient event occurs, a TVS protection device conducts and clamps the voltage at the VBUS pin to a defined level — the clamping voltage. This is the maximum voltage the system is exposed to during a surge event, and it is the most important specification for evaluating a protection device's effectiveness.

In conventional PN junction-based TVS diodes, clamping voltage increases with surge current and rises further with temperature, which means the device's worst-case behavior occurs precisely during the most demanding conditions. Additionally, downstream components must be specified to withstand those elevated clamping voltages which drive component cost and increase the required board area.

Semtech's SurgeSwitch architecture takes a fundamentally different approach. SurgeSwitch devices are built on a MOSFET-based topology that delivers a nearly constant clamping voltage throughout the full surge current range and remains stable over the operating temperature range. The result is a clamping voltage that is up to 30% lower than equivalent conventional PN junction-based TVS diodes, providing a larger safety margin for downstream ICs and enabling engineers to select components with lower absolute maximum voltage ratings.

Figure 2: Clamping voltage vs. Time comparison chart (TDS5311P vs. conventional TVS diode (SMBM58A)

Introducing the TDS5311P: SurgeSwitch for 48V VBUS Protection

The TDS5311P is Semtech's latest SurgeSwitch device, engineered to address the protection requirements of 48V VBUS lines in USB PD 3.1 EPR systems. Its working voltage of 53V provides the necessary headroom above the 48V bus rail, while its MOSFET-based architecture delivers the near-constant clamping performance that high-voltage USB designs demand.

Key Specifications

To illustrate the clamping voltage advantage in practical terms: a commonly used conventional TVS solution for 48V USB PD applications carries a clamping voltage of approximately 87V under similar test conditions. The TDS5311P's clamping voltage of 63V represents approximately a 24V reduction. This allows downstream components to be specified at a lower voltage tolerance, reducing both BOM cost and board space while increasing the overall design margin.

Figure 3: Semtech TDS5311P package diagram

Application: USB PD 3.1 EPR Systems

The TDS5311P is designed for applications where USB PD 3.1 EPR's 48V operating mode is in use. As shown in Figure 4, the TDS5311P is placed in parallel with the VBUS rail at the USB Type-C port entry point, providing a low-impedance clamp path to ground during transient events while remaining effectively invisible to the system under normal operating conditions.

Typical design targets for 48V USB PD EPR VBUS protection include:

• AI laptops and computing devices requiring 48V USB-C power delivery for high-wattage system loads
• High-performance docking stations where the VBUS rail powers multiple downstream devices simultaneously
• Portable power stations and power banks supporting USB PD EPR output
• Industrial embedded computing platforms with USB-C power input exposed to transient-rich environment

Figure 4: Simplified application circuit diagram showing TDS5311P placement on the VBUS line at a USB Type-C receptacle, with arrows indicating the transient current path to ground

Figure 5: Semtech SurgeSwitch Portfolio

Summary

While the fundamental requirement for USB VBUS protection has not changed, the limitations of conventional solutions have become more evident. Traditional TVS diodes, though widely used, suffer from drawbacks such as higher and variable clamping voltages as well as strong temperature dependence. These characteristics make them less suitable for modern high-power applications. Semtech’s TDS5311P SurgeSwitch addresses these challenges with a nearly constant 63V clamping voltage, 24A peak pulse current capability, full IEC compliance, and the inherent advantages of a MOSFET-based architecture — providing the performance and design margin needed for reliable USB PD 3.1 EPR systems.

To learn more about the TDS5311P or to explore Semtech's complete USB Type-C circuit protection portfolio, visit semtech.com/products/circuit-protection.

Semtech® and the Semtech logo are registered trademarks or service marks, and SurgeSwitch® is a registered trademark or service mark, of Semtech Corporation or its affiliates. Other product or service names mentioned herein may be the trademarks of their respective owners.