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USB Type-C™ Explained Lynnette Reese

I was intrigued to hear that Benson Leung, a Google engineer working on the Chromebook Pixel, had gone on a one-man crusade to help early adopters of USB Type-C technology (used in the Pixel) to review Type-C cables online to weed out the ones that were not USB Type-C spec compliant. Turns out that this amazing connector that will de-clutter our lives by channeling up to 10 Gbps data and 100W power in one small cable has many not-quite-right cables flooding the market.

The USB-C standard is somewhat new, and so cable markings or logos for USB Type-C certification are not clear yet for even the ones who are legitimately certified. This concerned me, so I checked with Qualtek’s engineer R.J. Nuti, to see if Qualtek’s USB Type-C cables are certified, and how to tell. R.J. had heard about Benson’s crusade and was very clear that Qualtek’s cables are indeed certified. He also said that the Superspeed+ (10Gbps) cables should have a SS+ USB mark on them.

Thanks Benson, for doing the right thing. And thanks for making me really curious about USB Type-C and why a Type-C cable can still be certified but unable to stream video to your 4K HD screen from your Type-C Chromebook. The hype on Type-C can be misleading, and there’s more to it than, “One cable to connect them all.” If you want the very short explanation, here’s my best advice: to avoid confusion, don’t ever buy anything but a cable that is certified as a Type-C, USB 3.1, and USB PD compliant cable. Yep, all three. If you want to know why, read on.

 

How USB became King of all Connectors

USB has gained wide international adoption for battery charging, especially for mobile electronic devices. Standardization on USB for charging devices has been primarily intended to reduce electronic waste by doing away with having a separate proprietary charger for every electronic gadget.

Three new USB technology specifications provide for USB solutions that promise to reduce clutter, provide unprecedented inter-operability, simplify connecting USB devices with reversible and “flippable” plugs and cables, and provide much faster charging. These improvements are specified in the USB Type-C™ and USB Power Delivery (PD) specifications that are compatible with USB 2.0, 3.0, and the new USB 3.1 specifications, cables and connectors in various ways.

 

 

 

But there are several independent (i.e., “mix-and-match”) USB specs:

1. 1. USB 3.0/3.1 (USB 3.0 =USB 3.1 Gen 1/SuperSpeed/5Gbps and USB 3.1= USB 3.1 Gen 2/SuperSpeed+/10Gbps)

2. USB Type-C™ (USB-C™)

3. USB Power Delivery (USB PD)

…and then there are the USB 2.0 and 1.1 specs.

But don’t confuse the specification USB 1.1 with USB Type-C 1.1.

Ultimately, when the current installed base of USB products are phased out, we will all use a single cable for everything, a cable that is:

1. Compliant with USB 3.1 SuperSpeed+  at up to 10Gbps

2. Uses the flippable, reversible Type-C connectors on both ends

3. And provides charging and data all in one cable for everything from smartphones to laptops to monitors. (Cool, huh?)

That indeed would be a single cable to connect nearly every gadget to power or another gadget. But we are not there yet. We still have many legacy USB products that will still be working 20 years from now, and no one is going to throw away a perfectly good Smartphone because its USB micro-B connector is annoying in the dark. You might have the Chromebook Pixel that only has Type-C connector receptacles (and is USB 3.1 Gen 1) and yet want to load images from our older USB 2.0 compliant digital camera, which has a USB micro-B plug. Therefore, until all these older USB products are phased out, you can have a Type-C-to-USB micro B connector/adapter/cable assembly that will never be able to implement the USB PD spec because the USB Type-B connectors were never designed to handle the voltage and current that a Type-C, USB PD compliant AC/DC charging cable (aka “wall wart”) would be able to provide to the Chromebook Pixel, for instance. Therefore, you will find chips, connectors, and cable assemblies that are both USB 2.0 and Type-C compliant, for example, and cannot charge higher than 1.5A or spew data faster than 480 Mbit/s (High Speed). Even if a cable is Type-C compliant, you will never need 10Gbps for your Type-C keyboard. Thus, we have cables that are USB 2.0-compliant and USB Type-C compliant that look exactly like a USB-Type C USB 3.1 (10Gbps) cable. I asked R.J. if there was a way to tell if a Type-C-to-Type-C cable was based on USB 2.0 or USB 3.1 speeds. He said there should be an SS+ marking on the USB 3.1 cable, otherwise they are visually identical. Since USB 3.1 is limited to 1m in length, I surmise that any Type-C cables greater than 1m long are the USB 2.0-chipped cables that will work for slower devices (<480Mbps, a.k.a. “High Speed”).

Right now, only USB Type-C cables and connectors can carry the power capability of (and compliant with) the USB PD (power delivery) specification, and Type-C can even operate in “alternate mode” to be used with other communications technologies like HDMI and DisplayPort.  (Scenario:  A new USB-C Smartphone connects to an older TV via a Type-C-to-Type C cable with a DisplayPort-to-Type-C adapter on your older TV.)

 

 

USB Type-C can do everything that all of these connectors do now, separately, and thus promises to seriously de-clutter consumer's lives. Image courtesy Cypress Semiconductor, AN95615

 

The USB Type-C spec mainly addresses how vendors will implement a USB cable with a connector that’s shaped something like a flat Chiclet. You can flip it over and the profile looks the same; no extra ridges to force you to get it just right. Type-C is tiny and robust. Type-C can deliver up to 100 Watts. But it comes at a cost: there’s a chip the size of a pepper flake inside the Type-C connector. The chip is needed in order to figure out which side is up or down, and which end is the “master” (host/DFP) and which is the “slave” (peripheral/UFP). Thus, the Type-C is both “flippable” and “reversible.” Clumsy smartphone users rejoice! The Type-C connector also has to know what type of power is needed (there are 5 profiles of 10W, 18W, 36W, 60W, and 100W.) One Type-C USB cable will be able to fast-charge and communicate simultaneously to a laptop from a monitor that’s plugged in to an AC adapter/”wall wart.” (That’s both charging, operating power, and video at the same time.)  The typical monitor may become a hub/docking station where everything is plugged in and inter-communicating while also charging.

 

 

USB PD standards create flexibility and concurrently deliver both power and data on a single cable. Image Courtesy Cypress Semiconductor, AN95615

 

For power, the Type-C cable must detect:

1. If the connected device will be providing or consuming power

2. How much power is needed (based on the power profiles.)

Devices that consume power with Type-C connectors must also comply to the USB Type-C standard in that they can consume at a pre-established power profile (choose from  5 profiles of 10W,18W,36W, 60W, and 100W at set voltages of 5V,12V, or 20V.)

But for the time being, we still have a bunch of smartphones, netbooks, laptops, mice, keyboards, GPSes and handheld gaming devices created to various (and backward compatible) USB standards. The Type-C physical connector is not physically backwards compatible, so you can expect lots of adapters to hit the market that convert Type-C to USB-whatever. Macbook Retina has a USB 3.1 Gen 1 (5 Gbps) multiport adapter that will communicate with other standard-A-port USB devices at 5Gbps, if those other devices are also USB 3.1 (Gen 1 or 2) devices. But do not expect your Type-C cable assembly to do more than USB 2.0 in charging or speed if that USB-C to USB-C cable is conducting communications with a USB 1.1- or USB 2.0-compliant device. It’s kind of confusing, and I think most people just want a cable they can trust, and having discussed all of this with R.J., you can trust the Qualtek 562-3023041-01M or the 562-3027001-005M to work with that Chromebook Pixel or the Mackbook Pro. Note that these are USB-PD compliant to 60W.

 

 

Qualtek 3027001-005M is rated at 10Gbps and up to 60W. Source: Qualtek datasheet.


Until all of your devices can use Type-C, buy adapters and take care to buy Type-C-to-Type-C compliant cables that comply with the USB Type-C specification. Better yet, make sure they are also USB PD and USB 3.1 compliant and you will not have to fuss with different cables for a good while. Without certification or logos that are earned by passing tests, you cannot be certain of Type-C cables or connectors from dubious sources. The form factor is just one facet of Type-C; Type-C connectors are smart connectors and will not work or may even damage devices if they are not fully Type-C compliant. (Drawing 100W over a non-compliant cable might burn up the non-compliant wires, etc.) Indeed, some Type-C chips (remember that pepper flake?) are Type-C compliant at USB 2.0 speeds. A human-device-interface (HID) class device will never need USB 3.1 speeds; no one can type that fast, therefore a keyboard may house a USB 2.0-compliant Type-C receptacle. (But a USB 3.1, USB PD and Type—C compliant cable will work just fine on that USB 2.0 Type-C keyboard, because USB 3.1 is backwards compatible with USB 2.0.)

So don’t confuse “USB Type-C” with a specific speed or power profile. Designers will need to confirm if a chip that supports Type-C also supports the USB PD and/or USB 3.1 if top-of-the line is needed in a Type-C compliant device or cable.

 

To learn more, see this 2 minute video from Cypress Semiconductor:

If you already understand USB standards and want a deeper dive, watch this excellent 38 minute video from Cypress Semiconductor:



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Lynnette Reese holds a B.S.E.E from Louisiana State University in Baton Rouge. Lynnette has worked at Mouser Electronics, Texas Instruments, Freescale (now NXP), and Cypress Semiconductor. Lynnette has three kids and occasionally runs benign experiments on them. She is currently saving for the kids’ college and eventual therapy once they find out that cauliflower isn’t a rare albino broccoli (and other white lies.)




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