Protection Solution for USB Power Delivery 3.1

Table 1. Fixed Voltage Power Ranges

With its launch, USB PD 3.1 will be seen in consumer applications, such as PCs, laptops, tablets, and smart phones. It will take USB power delivery into a bigger market, such as powered tools or electric two-wheelers. USB PD 3.1 is built upon the physical port of USB Type C, which not only allows improvement of transmission up to 40Gbit/s but also facilitates fast charging with the maximum power supply to 240W. This port is an exposed one on system that allows users to insert and remove as desired. The most common application is plug and play, and remove and exit. However, this seemingly harmless hot-swapping is often the culprit that cause malfunctions in electronics or even damage to USB Type C control elements, where this hot-swapping often introduces transient noises, such as electrostatic discharge (ESD). During a hot swap, the signal line at the port may have already been live, and this live line creates ESD as it makes contact with the system. An event like this is called ESD, which can do serious harm to systems. Direct discharge is the generic terms for such a phenomenon. When it comes to the ESD tests on system, more and more clients are asking direct discharge tests on products, simulating ESD events to which the system is subject in users’ hands.   

Now in addition to qualifying the ESD test specifications of IEC61000-4-2 on housing, more and more clients are specifying that the USB Type C ports on their products must be subject to direct-pin injection tests. It has been heard that some brand names requested simulation of direct discharge events that may occur to products sold in the plug-and-play maneuver by subjecting the system to bombardment of ±8kV ESD without any harmful effects. As a result, it is absolutely necessary to prevent the interference of ESD with data transmission with the use of protection elements in USB Type C interface. Figure 1 provides a typical direct-pin injection test setup. 

On the other hand, electronic products have reached every corner of the world. However, the probability that these products experience electrical over-stress (EOS) starts to grow due to poor infrastructures in many remote areas or the impacts of extreme weathers, and the result is that an increasing number of these products are returned for service. EOS usually comes from events like AC/DC interference, power noises or hot swap. At present, the EOS tests follow the IEC 61000-4-5 specifications, where the test voltage waveform is 1.2/50μs and current waveform is 8/20μs. Some brand-name manufacturers add EOS direct-pin injection tests in addition to the ESD direct-pin injection tests required in house. Figure 2 provides a typical EOS direct-pin injection test setup. 

For a USB PD 3.1 interface, the following need to be considered when selecting an ESD/EOS protection element: 

1. The critical parameter to consider is ESD and EOS clamping voltage: for an ESD/EOS protection element to provide effective protection, the element itself needs to survive sufficiently high ESD/EOS bombardment without damage, while a low enough clamping voltage must be taken into consideration, so that the ESD/EOS energy is suppressed to an even lower voltage to keep system circuitry from damage. This clamping voltage is the most important parameter to determine if an ESD/EOS protection element has what it takes to protect system circuitry. 

 2. This interface provides fast charging capability and supports multiple voltages of 5V/9V/15V/20V/28V/36V/48V. The frequent hot-swapping during charging may generate constant ESD/EOS threats to power line. It is necessary to have a better ESD/EOS protection solution on system against external surges.   

Amazing Microelectronic has a wide range of cutting-edge ESD/EOS protection design techniques, and has launched families of ESD/EOS protection elements at various voltages specifically for USB PD 3.1 protection needs, as shown in Figure 3 below. 

This port allows fast charging and, therefore, needs an ESD/EOS protection element at its power supply end. An appropriate ESD/EOS element selected based on design voltage helps protect the port from ESD/EOS threats. Figure 4 presents the protection circuit for a complete ESD/EOS solution for USB PD 3.1 interface.