Google Engineer Goes to War Against Bad USB Type-C Cables

The new USB Type-C standard has been adopted by many laptop and smartphone manufacturers this year for its superior power and data transfer capacities – with the added bonus that, unlike previous USB cables, there is no top or bottom – including Google’s Pixel laptops and tablets. However, it seems that many cheaper USB Type-C cables do not meet the official 1.1 specifications, and one man in particular is as mad as Hell and is not going to take this any more.

Benson Leung, a Google engineer who works on the company’s Pixel range of computers, has been testing USB Type-C cables found on Amazon, and he’s been left disappointed by their performance. Faults such as poor wiring or not being 3A compatible means that many of the cables on sale are not worthy of certification, and Leung has been leaving product reviews that make this abundantly clear to prospective customers.

Leung left the following two-star review of the TechMatte USB-C to MicroUSB adapter:

“I’m a Software Engineer on the Chrome OS team at Google on the Chromebook Pixel and Pixel C teams.

I bought these two USB-C to Micro USB adapters from TechMatte and found they do not work properly with the Chromebook Pixel.

Upon closer inspection by our engineering team here, we have determined that this adapter is not correctly following the USB Type C specification.

The specification can be found here :
http://www.usb.org/developers/docs/usb_31_102015.zip

Specifically, these adapters do not charge the Chromebook Pixel 2015 because the adapters leave the C-C lines floating, where the specification requires a Rp pullup to Vbus to identify the cable as a legacy adapter or cable.

Please see the document named “USB Type-C Specification Release 1.1.pdf”
section 4.5.3.2.4 for a description of why the Rp pullup is necessary.

Please also see Section 4.11 and the following note :
1. For Rp when implemented in the USB Type-C plug on a USB Type-C to USB 3.1 Standard-A Cable
Assembly, a USB Type-C to USB 2.0 Standard-A Cable Assembly, a USB Type-C to USB 2.0 Micro-B
Receptacle Adapter Assembly or a USB Type-C captive cable connected to a USB host, a value of 56 k’
± 5% shall be used, in order to provide tolerance to IR drop on V BUS and GND in the cable assembly.

In other words, since you are creating a USB Type-C plug to a USB 2.0 Micro-B receptacle assembly, you must use a resistor of value 56k’ as a pullup to Vbus. This cable does not do this.

Please let me know if there is any more information I can provide about why these adapters are problematic.”

Leung’s full Amazon review history can be found here, and it’s certainly worth referring to if you’re in the market for a new USB Type-C cable, especially as the engineer does give five-star reviews to the products that deserve it.

Image courtesy of Stuff.tv.