USB Type-C
USB Type-C pad distances are such that the voltage rating between adjacent contacts within the plug and receptacle fall well below the IPC-recommended distances as voltages get pushed up over time. The original PD specification allowed for up to 20 V to be delivered to a powered device, which falls under the typical ~30 V peak threshold for the tight spacings present in the USB Type-C connector design.
The USB Type-C receptacle/plug can have contact-contact spacings of only 0.25 mm (0.5 mm pitch with 0.25 mm nominal contact widths). The board side, however, typically drops down to ~0.15 mm on surface-mount pads, and annular rings on PTH pins approach ~0.15–0.18 mm, where minimum soldermask webs are the only thing maintaining the spacing—if present at all.
USB PD (Power Delivery)
As the power delivery standard evolved, the original 5 A / 20 V (100 W) max power capability no longer seemed adequate. Laptops with adaptors that deliver 130, 180, and even 240 W are now on the market, using barrel plugs to supply the required currents while keeping voltages below 30 VDC. USB Type-C has found itself in a similar situation—trying to satisfy the need for increased consumer power demands while serving as the one-stop shop for power adaptors and high-speed data interconnects.
USB Type-C cables, pins, and wires can only support up to 5 A continuous. That 5 A capability comes with significant complexity and analysis to ensure the implementation within a product is safe and provides long-term reliability.
PD 3.1
The latest PD specification now allows for 28 V (140 W), 36 V (180 W), and 48 V (240 W). This new 48 V requirement places fairly high voltage levels next to sensitive high-speed signal pairs with minimal spacing. The IPC-2221 standard has significant spacing requirement increases for voltages above 30 V—from 0.1 mm to 0.6 mm for uncoated external conductors.
Complexity
The complexity of the USB Type-C specification and Power Delivery standards deserves consideration. Did you know the Type-C specification now has a “liquid corrosion mitigation mode”? The spec covers how to detect liquids, test procedures, sample liquids… This 400+ page Type-C document, coupled with the 1100+ page USB PD document, makes one think the ideal cell phone or laptop should connect power and data wirelessly.
Sometimes we do things because we can and not because we should. Designs start out clean and collected—like good code—and then little add-ons accumulate. A few hundred revision cycles later, backwards compatibility in both software and hardware leaves you designed into something that wasn’t the original spirit of the idea. Is there an issue with having a dedicated power plug and a separate high-speed data path? What problem is solved by having one connector to rule them all instead of two?
Maybe, like software, hardware was destined to stand on the shoulders of giants. Much like import requests—a simple module call that hides thousands of lines of code in the background—we don’t have to understand it at that layer. But do we want to lose the ability to fully understand the hardware?
references