Power


Protecting USB-PD and PoE circuits from industrial power surges


By Rolf Horn, applications engineer, DigiKey E


volving 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.


22 March 2026


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


Components in Electronics


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


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.


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,


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