Protecting USB-PD and PoE Circuits from Industrial Power Surges

Evolving technologies, such as USB Type-C Power Delivery (USB-PD) and Power over Ethernet (PoE), continuously drive expectations for fast-charging applications and streamlined power design. With these protocols being used in highly integrated and industrial applications, protecting their circuits from electrical overstress (EOS) and electrostatic discharge (ESD) events is essential to ensure user safety and device reliability. However, as power demands increase across continually shrinking form factors, surge protection becomes more challenging.

This article outlines the evolving landscape of USB-PD and PoE technologies, illustrating the essential need for circuit protection. It then introduces transient diverting suppressors (TDSs) from Semtech and explains how these devices can be used to provide low clamping with excellent temperature stability in industrial and other applications.

The expanding power levels of USB-PD and PoE

USB-PD and PoE have become the standard for combining high-speed data communications and power into a single cable connection. Their data rates today far exceed 1 gigabit per second (Gbit/s), and in recent years, their power levels have seen a dramatic increase:

• PoE: In 2003, PoE (Type 1) initially provided 15.4 W per port for powering wireless access points. By 2018, PoE++ (Type 4) supported 100 W per port, enabling PoE in high-power applications such as advanced industrial cameras.
• USB-PD: In 2014, USB Type-C cables were required to support 60 W USB-PD for devices such as tablet PCs. By 2021, the USB-C PD 3.1 standard enabled USB Type-C to deliver 240 W to charge larger systems.

With such large power loads being transmitted through such finely pitched connectors, surge events have become a very real risk to safety and reliability in systems using PoE and USB-PD. This makes surge protection a vital part of product design, especially as these products become more compact.

Protecting space-constrained devices from supply voltage transients

For compact devices that are charged via USB-PD, high levels of design integration can increase the risk of surge events. For example, shorter distances between components make it easier for voltage spikes or ESD to cause arcing between traces. This arcing can damage components or cause data errors through increased electromagnetic interference (EMI).

Surge-related heat is more likely to cause insulator breakdown between pins, leading to arcing and short circuits that further damage nearby circuitry. When power spikes occur on I/O or data lines, a device’s more sensitive components are at risk of severe and immediate damage due to EOS or ESD.

Supply voltage transients can also compromise electrical safety and increase the risk of fire due to high-current short circuits. These factors make it essential that incoming power anomalies are quickly detected, and high voltages and currents are diverted away from critical application circuits before damage can occur.

For effective protection across many applications, transient suppression components should offer the following performance characteristics:

• Clamping voltages should be very close to the operating voltage of the protected circuit to ensure that even slight overvoltage or ESD events are suppressed. Suitable clamping will depend on the USB-PD or PoE standard used.
• A consistent clamping voltage, regardless of pulse current amplitude or operating temperature, streamlines protection in systems where conditions are varied.
• Surge and ESD immunity protection components must be highly robust to remain functional even during the harshest events, such as lightning strikes.
• Compact components suitable for increasingly space-constrained installations are required.

A novel approach to surge protection

Semtech SurgeSwitch TDSs are designed to meet or exceed these application requirements. This family of compact devices provides single-line protection against high EOS and ESD events for the full range of USB-PD and PoE operating voltages. Key specifications across the series include:

• Peak pulse current capability of 40 A at 8/20 μs
• Surge immunity to level 2 ±1 kV as per IEC 61000-4-5
• ESD immunity exceeding level 4 (8 kV contact and 15 kV air discharge)

The internal mechanism of the SurgeSwitch TDS (Figure 1) differs significantly from that of traditional surge protection devices, such as transient voltage suppressor (TVS) diodes.

Figure 1: The FET-based shunt mechanism of SurgeSwitch TDS devices offers consistent clamping in unpredictable surge conditions. (Image source: Semtech)

Instead of relying on a conventional PN junction for breakdown, Semtech TDSs use a surge-rated field-effect transistor (FET) to protect sensitive components from EOS and ESD events. Paired with a drive circuit, this FET is activated by a precisely tuned trigger circuit to form a voltage-controlled switch that acts as the breakdown mechanism. When a transient voltage increases beyond the rated breakdown voltage of a device, the trigger circuit activates the shunt FET, switching it on and diverting the transient current to ground.

By utilizing a FET-based switching mechanism with an ultra-low ON resistance, SurgeSwitch devices can achieve consistent clamping voltages across a wide range of operating temperatures and peak pulse currents. This enables the integration of USB-PD and PoE into more demanding industrial applications that require predictable surge protection to support deployments across a wide range of operating conditions.

Selecting the right TDS solution

Selecting the right SurgeSwitch device primarily depends on the working voltage of the application, as this determines the clamping voltage required for circuit protection. For higher voltages, the TDS5801P.C (Figure 2) protects one I/O or power line operating at 58 V, which is typical of PoE. This device is available in a 1.6 mm × 1.6 mm × 0.55 mm package for high levels of space optimization.

Figure 2: The TDS5801P.C provides robust surge protection for lines operating at 58 V. (Image source: Semtech)

The TDS5801P.C offers:

• Peak pulse power rating: 1,490 W at 8/20 μs
• Peak pulse current: 20 A at 8/20 μs
• Supply clamping voltage: 70.2 V (typ.)
• ESD clamping voltage: down to 4.4 V
• ESD voltage ratings:
  • Air: ±20 kV
  • Contact: ±15 kV

With a high pulse power rating and low ESD clamping voltage, the TDS5801P.C TDS is suitable for outdoor PoE applications such as surveillance cameras, remote meters, and networking equipment, where adverse weather can heighten ESD. In these applications, the extended operating temperature range of -55 to 125°C is also essential for maintaining consistent protection, regardless of seasonal conditions.

In contrast, the TDS0521PW.C (Figure 3) provides a solution for 5 V working voltages used in Internet of Things (IoT) devices and VBUS lines for low-power USB-PD. To serve highly integrated devices, the TDS is available in a 1.6 × 1.0 × 0.55 mm package, with side-wettable flanks for flat mounting.

Figure 3: With a compact two-lead package, the TDS0521PW.C enables surge protection in space-constrained designs. (Image source: Semtech)

Key specifications of the TDS0521PW.C include:

• Peak pulse power rating: 412 W at 8/20 μs
• Peak pulse current:
  • 40 A at 8/20 μs
  • 8 A at 10/1000 μs
• Supply clamping voltage: 8.7 V (typ.) for 40 A pulse
• ESD voltage rating: ±30 kV (air and contact)

For sensitive, low-voltage equipment, this device provides excellent protection against high-level surge events, especially when connected to the primary power source during charging.

For similar protection at 22 V working voltages, the TDS2261P.C (Figure 4) is a TDS suitable for mid-range USB-PD applications such as industrial tablet PCs. The TDS2261P.C offers:

• Peak pulse power rating: 1120 W at 8/20 μs
• Peak pulse current:
  • 40 A at 8/20 μs
  • 3 A at 10/1000 μs
• Supply clamping voltage: 27.7 V (typ.) for 40 A pulse
• ESD voltage ratings:
  • Air: ±30 kV
  • Contact: ±20 kV

Figure 4: The TDS2261P.C offers versatile protection for 22 V systems where short-duration pulse currents reach 40 A. (Image source: Semtech)

Despite being the largest of the SurgeSwitch devices, measuring 2 mm × 2 mm × 0.75 mm, the TDS2261P.C still offers a compact solution for high EOS and ESD protection in space-constrained devices. In addition to USB-PD, other target applications include storage devices and industrial sensors.

Conclusion

As USB-PD and PoE standards continue to expand power delivery performance, robust surge protection becomes challenging in highly integrated device designs. The Semtech SurgeSwitch series overcomes design challenges with clamping voltages that remain consistent across a wide range of temperatures and pulse currents. They also provide reliable protection from harsh power anomalies across different line voltages and operating conditions.