TopFeatured.com

Today’s consumers have quickly become dependent on mobile devices that incorporate the USB-C, or USB-Type C, communication interface standard—from smartphones and tablets to wearables and laptops. The USB port also doubles as the fast-charging port for most of these devices as well. As a result, designing robust protection against electrostatic discharge (ESD) and overheating conditions has never been more important.

The USB-Implementers Forum (USB-IF) has upgraded the standard through four major revisions.¹ It was first standardized in 1996 and has been evolving with higher speeds and allowing more power carrying capacity. The USB standard started with version 1.0 and has progressed through version 2.0, 3.x versions, and is currently up to revision 4, USB4. Table 1 lists the versions from 2.0 to USB4 and shows how the maximum throughput of each version has substantially increased.

Table 1. Evolution of USB standards showing increases in data transmission rates. (Source: Littelfuse, Inc.)

To handle higher data transmission rates and higher power delivery, the USB Type-C cable and connector standard has been updated to revision 2.1² and the USB-PD (power delivery) standard has been updated to revision 3.1. Figure 1 shows the Type-C connector which can implement the enhanced USB feature sets. The PD revisions allow devices to be charged and powered through the USB interface. The maximum power capacity has increased from 2.5 W (5 V @0.5A) through 100 W (20 V @ 5A) to, currently, an extended power range of 240 W (48 V @ 5A). The higher power capacity will open new powering and charging applications for USB-C such as gaming notebooks, docking stations, 4K monitors, and all-in-one computers.

Figure 1: USB Type-A and Type-C connectors. The Type-C connector has 24 pins compared with the 4-pins of the Type-A connector. The signal contact pitch for the Type-C connector is 0.5 mm. Click for a larger image. (Source: Littelfuse, Inc.)

Challenges to product reliability

While the evolving standards have improved data transmission rates and increased charging power, the standards do not directly prescribe specific methods for protecting the USB interface from external hazards. This article will address methods to eliminate the possibility of failure from ESD and overheating conditions. These techniques are essential for ensuring a more reliable and robust product.

Protecting USB ports from ESD

Electronic circuitry such as USB ports that are exposed to the external environment through cables and connectors are potential targets for ESD. ESD strikes can occur through direct contact from a person or through the air if a source of energy arcs to an electronic circuit. ESD strikes can be up to 30 kV or more with fast rise times and can melt silicon and conductor traces with currents up to 30 A. ESD, with this much energy, can cause total failure of components.

In addition, ESD strikes can cause more subtle damage. Current due to ESD can cause soft failures including a state change in a logic device, latch-up, or unpredictable behavior. This can lead to a corruption of a data stream. Data will need to be re-sent which slows down the data transmission rate. In the case of a latch-up failure, the system will need a reboot. ESD can also cause a latent defect in which a component still functions but is degraded and can fail prematurely.

Products need to be robust to ESD for high reliability. They must also comply with international standards such as IEC 61000-4-2³ to enable sales in all regions of the world. Figure 2 shows an ESD-simulated test waveform specified by IEC 61000-4-2 which a product must be capable of withstanding for CE certification.

Figure 2:  ESD test waveform as specified in IEC 61000-4-2.(Source: Littelfuse, Inc.)

There are a wide range of products available to protect communication ports from ESD damage. Figure 3 shows recommended protection components for lines on USB interfaces with up to 100 W power delivery capacity and extended power delivery range up to 240 W. The recommended components are transient voltage suppressor (TVS) diodes. Table 2 describes the component technologies and their respective features and benefits.

Figure 3: USB interface block diagrams showing recommended components (See Table 2) for protection from ESD. Click for a larger image. (Littelfuse, Inc.)

Table 2: Recommended USB protection technologies (Source: Littelfuse, Inc.)

For the USB 2.0 lines, consider using an SP3530 unidirectional TVS diode or equivalent. This TVS diode can safely absorb, without degradation, a 22-kV ESD strike, almost 3 times the 8-kV level required by IEC 61000-4-2. Typically, a low capacitance of 0.3 pF minimizes interference with signal transitions. This component is available in a 0201 surface-mount package designed to save PC board space.

The SuperSpeed lines require a component with the lowest possible capacitance to not degrade the high-speed data transmissions. For example, the SP3213 bidirectional TVS diodes, two diodes connected anode-to-anode provide a minimum of protection for ESD strikes up to 12 kV. These diodes draw typically 20 nA of leakage current to minimize circuit power consumption and are in a compact µDFN-2 surface-mount package.

For the sideband use (SBU) and configuration channel (CC) lines, consider the SP1006 unidirectional TVS diode. This component can safely absorb a 30-kV ESD strike in a µDFN-2 package. The SP1006 is a very rugged TVS diode and is AEC-Q101 -qualified for use in automotive applications of USB communication.⁴

The V_bus lines require TVS diodes that can withstand a higher level of power than the signal line protection devices. The SPHV series of 200 W TVS diodes protects a Vbus line with 100 W capacity. The SPHV diode withstands 30 kV from ESD strikes and is AEC-Q101-qualified in a surface-mount package. For the Extended Power Range interface, an example solution is the SMBJ diode. It has a higher peak power rating, 600 W, than the SPHV diodes and can absorb ESD strikes as high as 30 kV. Like the other recommended TVS diodes for USB ports, the SMBJ diodes are surface-mount components.

Each of the different TVS diodes serve a function necessary to protect a specific set of lines from ESD and do not interfere with the functionality of the line. Incorporating these diodes into the circuit will prevent immediate failures, soft failures, and latent, premature failures.

Recommended
The big problem with fast charging using USB Type-C cables

Protecting USB Type-C plugs and receptacles from overheating

The high density of the USB Type-C connector allows more opportunity for contamination from dirt and dust to cause resistive faults between power and ground. Combined with higher power on the V_bus line, the USB connector has a greater risk of overheating, which can damage the connector, cable, and the attached port electronics. The temperature rise can melt a connector or, in the worst case, start a fire.

The solution for preventing overheating is a digital temperature indicator designed to be compliant with the USB Type-C cable and connector specifications. The temperature indicator increases its resistance by at least five (5) decades when it detects a temperature of 100° C or greater. The example component technology referenced in this article is the unique setP digital temperature indicator from Littelfuse. Its characteristic curve is shown in Figure 4.

Figure 4: Resistance vs Temperature curve for a temperature indicator using the Littelfuse setP as the example. Click for a larger image. (Source: Littelfuse, Inc.)

As shown in Figure 3, the temperature indicator is placed in the configuration channel line. It is not placed in the V_bus line so that it does not drop any voltage or power and does not reduce the capacity of the power delivery on the V_bus line. If the component detects the temperature reaching 100° C, its resistance increases substantially. The USB protocol interprets the high resistance as an open connection between the source connection, V_bus, and the sink connection, the load, and the V_bus line is de-activated.

When the condition causing the overheating is corrected and the temperature of the sensor falls below the 100°C threshold, its resistance resets to its low-temperature value of around 10 Ω and V_bus is re-energized. For best results, the temperature indicator should be built into a USB plug and/or receptacle so that it can monitor the connector temperature at the source of the fault.

Unlike a positive temperature coefficient device or a mini-circuit breaker which must be in the V_bus line, a digital temperature indicator does not consume power and reduce power delivery capacity. Furthermore, these other components are limited to 100 W and lower power which would prevent their use in the extended power range USB Type-C application.

The temperature sensor should be small in size so that it enables detection at the source of faults. It should also be able to change its resistive state in as fast as one (1) second to prevent damage to the cable and electronic components. Figure 5 shows how a temperature indicator maintains a safe connector surface temperature during an overtemperature fault.

Comparison of the lower rise in connector surface temperature when a temperature indicator (A Littelfuse setP) is used for overtemperature protection. Click for a larger image.(Source: Littelfuse, Inc.)

Summary

Without the proper protection, ESD or debris in USB Type-C connectors can cause field failures in the valuable consumer electronics upon which users rely on a daily basis. Electronics engineers can protect their latest designs by using TVS diodes to protect the USB lines from ESD and digital temperature indicators to protect connectors from overheating. As mobile devices become smaller and more complex and the demand for faster charging continues to increase, designers face the additional challenge of finding smaller surface-mount protection components to accommodate the limited space and minimize the PCB real estate required to put in place the necessary protection methods.

Forethought about these important design considerations helps prevent problems for the end users. It also contributes to more robust product performance, a longer product lifetime, and greater consumer satisfaction.

References:

¹USB-Implementers Forum website: Front Page | USB-IF.

²Universal Serial Bus Type-C Cable and Connector Specification. Revision 2.1. May 2021. USB Implementers Forum (USB-IF), Inc.  USB Type-C Cable and Connector Specification Revision 2.1 | USB-IF.

³IEC 61000-4-2Electromagnetic Compatibility (EMC) – Part 4-2: Testing and Measurement Techniques I Electrostatic Discharge Immunity Test. International Electrotechnical Commission. Edition 2.0 December 2008.

⁴Automotive Electronics Council website: AECMain (aecouncil.com).

Digital Temperature Indicators for USB Type-C Cables Design & Installation Guide, Littelfuse, Inc., April 2019, updated Sept. 2021

About the author

Todd Phillips is the global strategic marketing manager for the Electronics Business Unit.  He joined Littelfuse as a sales engineer in 2006 for the industrial POWR-GARD business unit.  Todd joined the electronics business unit in 2011 as a regional sales manager.  His current responsibilities include development of marketing collateral material, management of marketing activities for new product launches, and performing market studies and feasibility analyses for new product ideas.  He received his BSEE from Milwaukee School of Engineering.  Todd can be reached at tphillips@littelfuse.com.

The post How to protect USB Type-C connectors from ESD and overtemperature appeared first on Electronic Products.