USB Type C and 3.1: clearing up the confusion

by: Robert TriggsNovember 20, 2015

The arrival of USB Type C connectors and the faster USB 3.1 standard should be heralding a new age of consumer convenience. However, there seems to be quite a bit of confusion about what these new standards mean, and Google Engineer Benson Leung also recently spotted that a number of cables weren’t exactly matching up with the latest USB specifications properly.

So, let’s clear all the mess up by taking a closer look at the new technology and what companies are and aren’t doing correctly.

Standards (ill-)defined

First, we should clarify that although they may often appear together, USB Type C and 3.0 or 3.1 are not synonymous. This means that you can have a USB Type C port that supports slower 2.0 data transfer speeds, or an older USB Type A port sporting faster 3.1 compliant speeds.

For example, OnePlus recently stated the following with regards to its new connector:

The OnePlus USB Type-C cable and adapter are compliant with USB 2.0 and Type-C 1.0 protocols.

Not exactly crystal clear, huh? Furthermore, the USB standard has grown over the years to include a number of additional power specifications to cope with the needs of more powerful devices and new technologies. This includes six different USB Power Delivery profiles that work across USB 2.0 and 3.1 products and the USB Battery Charging specification. The USB-Type C 1.1 specification also carries its own power operation modes, which is design to quickly charge up compatible gadgets and laptops. More on that later.

As part of the Power Delivery standard, a new power management system was introduced that uses a new bidirectional data channel to request certain levels of electrical power. This is to ensure compatibility with legacy devices and minimize the damage from non-compliant cables.

Here’s how the base USB specifications compare:

 USB 1.0USB 2.0USB 3.0USB 3.1
Data Rate12 Mbps480 Mbps5 Gbps10 Gbps
Default Power2.5W (5V, 0.5A)2.5W (5V, 0.5A)4.5W (5V, 0.9A)4.5W (5V, 0.9A)

The only major difference between USB 3.0 and 3.1 is that the latter supports double the peak data speeds of the original. Most devices are likely to jump straight to 3.1, but developers have a task on their hands making sure that they support the two latest standards while retaining backwards compatibility.

When it comes to speed, you will be limited by the slowest component in your chain. Connecting a USB 3.1 devices to a USB 2.0 port will limit your speed to 480 Mbps, for example. In reality, hardware components like a hard-drive are likely to be limiting factors as well.


USB Type-C is a reversible interface, unlike (left to right) micro-B, Type-A, Mini-A, and Type-B.

So essentially, USB Type C refers to the reversible connection type, while the version numbers refer the data transfer speeds and other specs that a port or cable supports. However, neither of those parts strictly define the type of USB Power Delivery specification or the peak current that the device or cable is compatible with.

There’s an awful lot of potential cross over here and it can be pretty confusing. Part of the problem with USB is trying to accommodate older devices while simultaneously pushing forward with new technologies. Hopefully this table helps to explain how the different power standards compare to one another, and in what order of precedence they are given by devices.

USB Power Sources

Good and bad cables

Ok, if you’re still with me we can begin to make sense of some of the latest news around these standards and unravel a bit of this mess when it comes to cables and connectors.

USB Power Delivery CableFor devices making use of USB Power Delivery, communication is exchanged over the connector’s CC pin, which was introduced with the new 2.0 standard. This communication configures the right power between the charger and device, allowing for up to 100W of power at its most extreme, using up to 20 volts and 5 amps of current. This mode is most likely to be used by laptops and other more power hungry devices, as it supports higher voltage modes.

A handshake between micro-controllers overwrites all of the lower power modes and sets up the correct voltage and current settings, while no handshake means that these higher power modes can’t be activated. This also means that lower power use cases, such as smartphones, can be covered without this extra technological cost.

For the basic USB Type-C 1.0 and 1.1 standards, 5V devices can be powered with up to 3A of current using the same pin but without the need for USB PD. Rather than sending configuration data over the CC pin, the pin is pulled up to the 5V supply rail and the current coming into the pin is monitored to determine the output power requested by the device. The amount of current is controlled by the pull-up resistor Rp, and setting it to specific values sets the device to draw either 0.9A, 1.5A or 3A.

USB Type C pull up resistorFor Type-C to Type-C connections, using these higher current modes is fine, as the ports are all built around the same standard, and is a convenient way to charge devices up quickly. However, a lot of the recent issues have been about legacy adapter cables, the ones that will take your USB-Type-C socket on your new phone or laptop and connect up to an older Type-A PC port or charger.

usb-type-c-3See also: Beware of cheap USB Type-C cables, warns Google engineer7

We’re not worried about speeds here, but the thing to look out for is power transfer between devices. Because the USB Type-C standard specifically defines higher rates of charging that aren’t catered for in older Type-B or other connectors, cable manufacturers are supposed to use the CC connection and Rp resistor to ensure that devices don’t attempt to draw too much current from older chargers or devices that can’t support it.

The specification table below shows what values can be used to set a specific Type-C charging mode and underneath, in the small print, we can see that a 56kΩ resistor should be used with all legacy cable connections. This is to limit the amount of current transferred to Default USB power or the USB Battery Charging standard (if the cable supports fast charging) when connecting up to older USB type devices.

USB resistor requirements

What has happened with the case of OnePlus and the other out of spec USB adapter cables is that they are not setting this resistor properly. A number of companies are opting for 10kΩ values, perhaps mistakenly thinking that they are meeting the maximum capabilities of the specification when in fact they are breaking it. This could mean that a USB Type-C device attempts to draw 3A from an older charger than can only handle 1A or less, a recipe for destroying your charger or port.

Another part of the issue is that cables also want to support fast charging technologies for smartphones and other products. This often falls under the USB Battery Charging standard, which supports higher currents than the default mode. Manufacturers may be mistaken into thinking that the correct way to cater for these currents is to allow for the maximum of 3A over Type-C. However, communication for this standard is managed over separate USB D+ and D- data lines, rather than the CC line, and is usually handled by an on-device power management circuit. The 56kΩ resistor is still required, as we know that the Type-C modes overwrite the USB BC standard.

What-is-USB-Type-C-video-thumbnailRead on: What is USB Type-C? How does it change the game?30

Picking the right cable

Hopefully now we’re all clued up and on the same page. There are a ton of different USB charging options out there and when it comes to backwards compatibility, you want a cable that is set-up to correctly support older hardware.


USB 3.1 offers the fastest data speeds, but only if devices on both ends of the cable support it. Remember, they don’t both have to be USB Type-C connectors.

A big part of the problem is that there isn’t a very easy way to figure out if the cable you are intending to buy actually has this resistor set correctly, at least not without whipping out the ohmmeter yourself. Obviously, using the one that comes with your device is a safe bet and buying a replacement from the manufacturer is usually wise, but it might be easy to forget that this cable might not always work correctly with other devices (as is the problem with OnePlus’ cable).

Unfortunately, datasheets and details are not readily available for most cables, and descriptions can be misleading, as support for 3A doesn’t really tell you if the cable has been configured correctly. Instead, try to find the official product page from the manufacturer and look for mention of USB-IF Certification and markings on the cable or packaging. The USB-IF is a non-profit organization that tests products to ensure compliance with the standards. Although not every reliable manufacturer goes down this route.

USB-IF certified logos

Google Engineer Benson Leung also has quite a growing collection of USB cable reviews on his Amazon account. Picking any of the ones he has given a high rating too is a safe bet, and be sure to steer clear of any of the cheaters that he has spotted.

  • Randy_Thompson

    Has anyone found a good USB Type-C car charger? I’m looking for something for my Nexus 6P/my boyfriend’s Nexus 5X that will do the trick and, if possible, put out enough power for the phones to charge rapidly. Doesn’t seem like Benson Leung has a lot reviewed on his end for this instance – he has just one, but it’s not highly rated X.X

  • James

    Got a nexus 6P here. Will the charger that came with that also charge some of the new laptops or hybrids that are coming out which charge with USB-C? Specifically the Macbook, Google Pixel, Hp Elite X2 1012 or Hp Spectre X2.

    It would be cool to only have to carry around one charger.

    • Yes

    • nxtiak

      Yes, but you should buy the 60W charger, fast charge your Macbook/Pixel2!!!!

      • James

        Cool, thanks for the advise! I assume the 60W charger is still safe for the Nexus 6pp?

        • M3D1T8R

          Confirm elsewhere because I’m not 100% sure but I believe it should be. Modern devices are generally smart enough to draw the right amount of power even if the charger is rated for much higher amperage than the device needs.

        • Aaron

          Yes, it would still change your Nexus 6P at 3A

  • PlatinumX

    Just to make things more confusing, USB 3.0 (5Gbps) has been renamed USB 3.1 type 1, and USB 3.1 (10 Gbps) is now USB 3.1 type 2.

    • Michael Benvenuti

      I thought they referred to it as gen 1 and gen 2.

  • Sashimi

    … And then people wonder why apple came up with lightning ports and and drm’ed cables.

    My god tech engineers should be required to see a bit of day light now and then…

    • Jared

      Cables don’t have DRM. It’s proprietary…

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      • Sashimi

        yes they do. look it up (and it was cracked, obviously). DRM is not perfect, but in this case, it buys useful time.

    • There is nothing wrong with the cable. It is perfect. And has a certification and rules to follow. But companies don’t want to follow them.

      • Sashimi

        Certification & rules are techfapping material if they aren’t followed by hardware manufacturers. Add to this non-certified stuff displaying fake certification logos… Thus the DRM approach of apple.

      • JohnW

        There is plenty wrong with the specification though. If they had omitted the 1.5A and 3A type C modes they could have eliminated all the confusion. Cables should be as simple as possible to avoid the issues we are seeing.

  • 1213 1213

    So is there anything about plugs that we need to know?

    • s0uLjah

      Do you mean the wall adaptor or charging brick? I have the same question too.

  • Michael Benvenuti

    Great article, I have been reading through the the USB Type-C and USB PD Specification Release and this really nails the key parts.

  • Olav

    Ok this is enough…. besides that 90% of the world uses underpowered supplies to their devices i have to say one thing only : Seriously? You are going to discard a company that made people drool
    over the specs and prices based on some guys comments about a CABLE????
    Talk about looking at the finger and missing the forest….. ( i am not
    even mentioning that he is probably paid from samsung or apple to put
    himself out there, open your eyes people, this is how big companies do
    when they cant win otherwise… a RESISTANCE in the cable???? LIKE how
    many houses have been burned down in the last 6 months from OP2 cables
    charging nexus devices???? HOW MANY??? THINK dont be SHEEP….. )

    • The certification has a protocol that must be followed. OnePlus is not following the protocol. That is why it’s cheaper.

  • Aaron

    Rob Triggs, regarding the second image, you’re supposed to put a Type-B male instead of Type-B female. You’re painting a wrong impression for the readers.

    • He didn’t say Type B female, he only said Type B ?

      • Aaron

        When we talk about USB Type, we always use the male as the standard. That’s why you see the other 3 are male. Got it?

  • s0uLjah

    Do the wall adaptors matter? My adaptor that came with the 6P is pretty much done, unless it’s the cable, but would it matter what type of third-party adaptor I buy so I can still utilize the Type-C to Type-C cable that came with my phone?

    P.S. please be gentle, I am so new to all of this cable, power, resistor talk, I may end up with more questions. I hope the above question is easy enough to answer.

  • mr.pedro

    Can I use any usb type-A to type-B cable with usb type-c adapters? Or usb type-A to type-B cables can be also unsupported?

  • Sebastián Greco

    I get so confused with so many web pages explaining technical details about standards and specifications. May any of you give me a good and simple to understand rule for buying a cable. No explanation needed:
    – 56kΩ resistor is necessary only for Legacy USB Type-A to USB 3.0 Type-C?
    – If I have a Type-C charger (like the one it comes with Nexus6P), does that cable need to have 56kΩ too?

    We have 2 mobiles at home. 1 Nexus 6P and 1 Huawei P9 (AL-029, yeah, the chinese ROM version). I want to buy chargers and cables for both of them. For home, car and computer use. Have no idea whatsoever what to buy. Of course, I could go with manufacturer ones but that’s way too expensive and wouldn’t cover all our needs.

    • Homero Garza



      I don’t understand how a type c charger is expected to be 3 amps though.

      • JohnW

        You are not alone. Even manufacturers don’t understand it.
        It appears you want a 56kΩ resistor unless you are using one of the more perverse modes in which case you device manufacturer will supply a special cable probably affixed to a charger.

  • BenT9

    are there any phones that support 3.0 or 3.1 speeds?

  • Adamya Agarwal

    I want to know one more thing. Oneplus 2’s OTG only works with oneplus usb type-c adapter( 10k) and not with any standard usb type-c adapter(56k). I know that the adapter is non-conforming but is the oneplus 2’s usb type-c port also defective? I mean to say is this a hardware defect or software defect.