The evolution of USB Type C in power-only applications
Since their inception over two decades ago, USB connectors and their associated standards have gone through an array of advancements to both their data transfer rates and power capabilities as well as multiple iterations of the physical connector itself. Introduced in 2014, USB Type C is the latest physical standard, well-recognised for its simplified, bi-directional package, higher data rates, and greater power delivery.
By Jeff Smoot, CUI Devices
As has already been alluded to, USB connectors are defined by these three different, yet related standards: the physical connector, data transmission protocol, and power delivery. However, the relationship between these various standards is often misconstrued. Prior to diving into the evolution of the power-only USB Type C connector, CUI Devices’ clarifying the connection blog post provides a good primer on the various USB standards.
Comprehending the USB Standards
At a basic level, the USB Type C standard only represents the physical connector found in today’s electronics such as cell phones and laptops. USB 3.2 and other data transfer protocols are only concerned with the electrical signal. These standards are quite synonymous with one another, but it is possible for a designer to utilize a data transfer protocol like USB 3.2 in their system, while implementing a proprietary connector not associated with any of the physical USB connector standards.
A similar logic also applies to the USB Power Delivery (PD) specification. Supporting up to a 5A current rating and 20Vdc voltage rating, USB Type C connectors can deliver up to 100W of power as defined in the USB PD 3.0 standard.
But, again, while often seen together, the Power Delivery specification is really controlled by the charging circuit and only limited by the voltage and current rating of the physical USB Type C connector. However, it is USB Type C’s higher power capability that has created new opportunities for it in the world of power delivery.
Figure 1: USB PD levels
The Benefits of USB Type C in Power Designs
A standard 24-contact USB Type C connector supports up to 100W of power transfer with its 16 data transfer contacts, 4 power contacts, and 4 ground contacts. When data transfer is not needed, USB Type C has become an attractive option for power applications capable of replacing a standard dc power connector.
It is USB’s standardisation that gives it an advantage as a method for power delivery. USB connectors are everywhere, while USB Type C continues to gain momentum as the universal connector in many electronic devices. In fact, the European Union is already pushing to make Type C the connector standard for all devices sold in its member countries. It cannot be understated how much convenience is provided to the end-user by only requiring a single, off-the-shelf cable to connect to a wide range of devices.
End-users are not the only ones who stand to benefit, as OEMs also have access to a stable supply chain due to USB’s widespread use, while its standardization affords a level of interoperability and simplified design integration. USB Type C connectors also feature a smaller footprint than most dc power connectors and carry 10,000-mating cycle ratings for added robustness and reliability.
Introducing Power-Only USB Type C Connectors
As a result of the benefits listed above, CUI Devices has introduced power-only USB Type C receptacles for designs where power delivery or charging is the singular function. CUI Devices’ 60 W power-only USB Type C receptacle accomplishes this by removing the 16 data transfer contacts and 2 of the ground contacts, leaving only 4 power contacts and 2 ground contacts. On the other hand, the 100 W version maintains all 4 power and ground contacts for 8 total contacts.
Figure 2: 24-contact USB Type C vs 6- and 8-contact power-only USB Type C
In removing the 16 data transfer contacts, the simplified design of the power-only USB Type C connector leads to a substantial cost reduction with only 6 or 8 contacts instead of the standard 24. Not only is the part cost reduced, but also the complexity and failure rate with fewer contacts and solder joints that could potentially fail. One might think that because these connectors do not transfer data that they require a special power-only USB Type C cable as well. However, this is simply not the case, as they can interface with any standard data+power USB Type C cable, further adding to their convenience with no additional hardware or requirements needed to function.
It is important to note that with no data transfer pins, the USB 3.0 power negotiation process does not occur. This means that the charging device will default to the USB standard power transfer rate of 5V and 1A. For all other cases, the power-only USB Type C connector will operate like any other power jack with the charging governed by the adapter/charging circuit.
Additional Power Considerations
USB Type C connectors have found a home in a multitude of applications, but dc power connectors and other dedicated power connectors still have their uses. First of all, with a hard cap of 100W, USB Type C connectors are not suitable for designs needing more than that amount. A USB Type C’s standardised footprint also offers a range of advantages, but it can be a limitation if a design requires an alternate footprint or package size.
Simply put, if a more highly customised solution is needed, USB Type C could be hampered by its standardisation. For further information on when other power connectors can still be the best option, read CUI Devices’ blog on selecting a dc power connector.
USB Type C Moving Forward
USB Type C connectors have opened a new window in which to look at power management and transmission thanks to their power capability up to 100W and global standardisation. CUI Devices’ power-only USB Type C receptacles, with their low cost and simplified design integration, give designers a worthwhile option when power delivery is the lone function.
CUI Devices currently carries a 60W power-only USB Type C receptacle with a 3A max current and 20Vdc max voltage. A 100W version is also available that features the full 5A max current and 20Vdc max voltage supported by USB Type C connectors.