USB – UNIVERSAL SERIAL BUS
A standard for data exchange?
USB has evolved from bulk data transfer capability to an allround and multi functional interface, featuring data, power, audio and videosignal transfer. More functionality comes at the cost of confusing naming, specifications and classifications, resulting in significant performance differences.
Starting with data transfer rates of 480 Mbit/s up to a multi functional interface featuring up to 100 watts of power. Let´s summarize what the USB interface is capable of and under which conditions. Let´s also talk about features like USB 3.1 Gen2, USB Power Delivery and USB Type-C.
An USB chain primarily consists of a host controller (source), USB ports, USB hubs, slave clients (device, pit) and cables. The host controller usually is the PC. USB ports and hubs are like multi outlets, while slave clients are connected peripherals. Keep in mind: A chain is only as strong as it´s weakest link. In this setup even the connectors at the end of each cable play an important role.
USB cables are data and power lines at the same time. A proper shielding of the cable is mandatory for a reliable communication. Keep in mind: Higher transfer rates require better, more advanced shielding. A special way of keeping the signal clean is a so called ferrite-choke, which is mainly used in combination with self-powered devices e.g. 2.5“ HDDs or slimline DVD recorders.
Recent USB standards as well as USB Power Delivery require even more advanced cables. The conductors of the cable have to be extra strong to be able to transport the higher current. A lower AWG (American Wire Gauge) number indicates thicker, stronger conductors. Usually in the range of 20-28.
These cables also act as a means of linking host- and slave-clients. They ensure a proper handshake in regard to power transfer capabilities between both devices. Real world setups show that low quality cables may very well lead to damage to the connected devices.
USB plugs usually are either Type A or Type B: While Type A is wide and flat and is usually used to connect the host side, Type B is almost square and is usually connected to the device end. For small, mobile devices, like MP3 players, digital cameras or cell phones, both ends are made of the Mini- or Micro version of each type. The modern replacement of the mini-USB plug is the Micro-USB plug, which is especially used with mobile universal chargers. Micro-USB is the smallest USB plug. The micro version also has Type A and Type B connectors, which look almost like their larger brothers in form and shape. With cell phones and smartphones the micro USB connector is widely used, so that chargers of different manufacturers may be used for each device. This is subject to change due to the multi functional USB Type C connectors. In tight lock with USB 3.1 Gen2 and not prone to the classic host / client role assignment, you can find more information regarding USB Type C in another chapter.
What is my USB connection capable of?
To understand which USB interface does what, it is important to distinguish between the different speed classes, plugs and specifications. The most recent USB specification is USB 3.1, also called SuperSpeedPlus. This specification also incorporated the older USB 3.0, SuperSpeed standard. That is why one differentiates between #1 and #2 generation. USB 3.1Gen1 (SuperSpeed, former USB 3.0) and USB 3.1 Gen2 (SuperSpeed+)
The full potential of USB 3.1 Gen2 is only supported by the new USB Type C connectors. This is not valid vice versa. USB Type C is only a connector, not supporting any features of USB 3.1 Gen2. Also new and independent by the USB standard is USB Power Delivery - a specification to transfer power over the USB interface.
USB classifications and versions
The most recent USB classification USB 3.1 Gen2 features double the data rate compared to it´s predecessor. SuperSpeed+ provides data rates of up to 10 Gb/s (Gigabits per second). The maximum charging current is 5A and ensures proper supply of up to 100 watts for devices featuring USB Power Delivery (USB PD 2.0).
This speed is supported by Type C connectors, USB 3.1 A, B and Micro-B, while only USB Type C is able to support the full feature set of USB 3.1 Gen2. This is especially true for compatibility to alternative interfaces like Thunderbolt, HDMI ans DisplayPort. USB Type C features video and audio transfers as well. You want to know more? Head over to USB Type C.
Every day use: It is even possible to transmit uncompressed UHD video signals via USB e.g. from a camera to a display. Devices using up to 100 watts are supported directly using an USB connection. This allows the user having only a single USB connection to power the display and yet at the same time transfer audio and video data using the very same connection.
Predecessor is the classification USB 3.1 Gen1, also known as USB 3.0 back then, supporting 5Gb/s max. data transfer rates (SuperSpeed) and 900mAh current. USB 3.1 Gen1 is backward compatible to earlier versions and features duplex data transfers, so data can be transmitted in both directions at the same time. These advantages are made possible by five additional lines, which also change the requirements in regard to the cable. The cables are a little thicker and less flexible. Connectors of this classification are USB 3.1 A, B and Micro-B.
USB 2.0 is only able to transfer data using HighSpeed (480Mb/s) and current of up to 500mAh, resulting in a power of max. 2.5 watts. Connectors of this classification are USB 2.0 A, B and Mini-B as well as Micro-B.
A glimpse of the future: USB 3.2
The USB implemeters forum will announce USB 3.2 in July 2017. The specification shall be released in a timely manner and will provide 20 Gbit/s using Type C connectors.
Along USB classification, USB ports and cables the plug types play an important role in regard to the efficiency of a USB connection. That is why the USB 3.1 Gen 2 specification needs a more capable connector. The new USB Type C connector (USB-C) will be device indepedent the one single way of transporting data, power and video information. This uber-USB incorporates speed and power in a compact design and will not only support regular PC setups but also mobile applications and smartphones, tables, notebooks... you name it. Manufacturers like Apple and Google are already focusing on one single type of connector: The USB Type C port.
Here is an overview showing the most important new features of the Type C connector:
- No up or down anymore, the connector fits in any direction to the socket.
- No discrimination anymore in regard to host or client device e.g. PC and printer. So one single cable fits both ends, since it got the same plug on each end.
- Small, compact and an inexpensive design: The socket only needs an opening of
8.4mm by 2.6mm. The design features a center board mounting to be able to use both sides of the PCB.
- Longevity: Compared to Micro USB the new Type C connector features 10.000 connection cycles.
- Backward compatibility is provided by adapters.
- In part it is still compatible to other standards like Thunderbolt or DisplayPort.
- 2x 12 connectors
There are no longer defined host/client role models in place. The roles are automatically installed betwenn both parties of the USB Type C devices using a handshake during linkup. One differentiates between data source and sender, power source and sender, as well as multi-functional ports which are able to be both at the same time, power and data source and sender.
USB Type C at first is only a connector, not mandatory featuring all USB specification 3.1 Gen2 or other audio and video standards. This featureset is defined by the host´s chipset.
USB 3.1 Gen2 can be operated in an alternate mode using Type C connections, rendering it compatible to other interfaces. Other, non USB protocol links like Thunderbolt 3 with up to 40 Gbit/s, MHL, PCI Express, Display Port (device dependent up to DP 1.4) as well as HDMIconnections can be created. Using MHL a smartphone can be connected to a display, while at the same time the display charges the smartphone. This connection can be established by using USB Type C to USB Type C, HDMI Type A or Micro-USB.
USB Power Delivery
USB Power delivery (PD) is a specification for transferring power via USB and supporting power ranges of up to 100 watts. This specification is not dependent in regard to the USB standard, but builds on it and is available starting with USB 2.0 e.g. by Type A and B plugs.
USB ports are widely used, e.g. in notebook computers, cars, planes and even as a wall outlet. At the same time electronic devices tend to use more and more energy and often resort to the USB standard. USB Power Delivery features the highest possible functionality of USB by supporting more flexibility at the power level while at the same time using one single cable to transfer data.
How does USB power delivery work?
Using USB Power Delivery the source, receiver and cable communicate with each other to determine the highest possible power rating. By default USB provides 0.5A to 5A (USB 2.0 to 3.1 Gen2, only using the Type C connector). This provides up to 25 watts of power. Using USB Power Delivery source and client do a handshake to determine the power and voltage. There are more different protocols in place to support additional voltages (e.g. 12V and 20V), which are to be enabled by handshake between source, receiver and cable. This enables the USB Type C connector and USB 3.1 Gen2 reaching 100 watts using a voltage of 20V. Using USB Power Delivery even with USB 2.0 or USB 3.1 Gen1, higher power rates are supported. The directional flow of the current is no longer fixed. The device connected proving the better power source is providing the power to the other one. It is no longer important whether it is a host or peripheral device. e.g. a fixed display may charge a smartphone or tablet connected to it.
To ensure it is possible to even charge turned off devices and to make sure a smartphone does not charge the notebook computer, there is a pre-defined direction of power flow in place, which is active even without operating system or a turned on device. To achieve this USB Power Delivery defines power receivers, providers and combi-devices. By handshake between these devices along with the cable the power flow direction is determined and the maximum power is set by profile. The directional power flow as well as the providers and consumers may be selected freely within the USB tree. USB Power Delivery demands high standards in regard to the cable. These cables are active and include their own chipset, which is doing the handshake between the devices and setting the power profile. The power source lists available current and voltage rates while the receiver selects the matching combination and requests it using the cable. The cable is the central point of communication. Is too much power provided, e.g. because an old profile is still active, the device may get damaged. Especially with USB Power Delivery cables you want to be on the safe side and always resort to proven InLine quality.
To ensure everything works even in combination with older devices, USB Type A connectors are providers while USB Type B connectors are consumers. If there is no problem, the flow direction is set automatically once connected.
Please note, The current is set by the cable and it´s plugs. A regular cable will support 7.5 watts (5V, 1.5A) and an active USB Type C cable will support 15 watts. Using Micro-USB connectors there is a upper limit of 60 watts (3A). USB Power Delivery requires USB Type C connectors on both ends at the higher power profiles.
The optimized USB Power Delivery management allows to provide each device with the power it currently needs. The power profile may be set higher if the device requests more power. This is also true for a PC and hub communication or for devices with very low power requirements, like headsets.
Every day use?
That means a display featuring an external power source, e.g. a power supply, will support a notebook using the USB connection. Other devices like HDD drives, printers etc. do not need their own power supply anymore. USB-Powerbanks or power supplies will support powering devices like notebook computers using their USB port. The other way around notebook computers may charge the batteries of e.g. a smartphone at much higher rates. Currently there are only a few devices and accessories supporting USB Power Delivery available. Most recent smartphones, tablets and notebooks featuring an USB Type C connector, like the One plus 2, Microsoft Lumia 950 and 950 XL, the Google Nexus 5x and 6P as well as the new Apple MacBook and some chargers are already supporting the new technology.
The USB Power Delivery specification was revised several times now. There are Rev. 3.0, 2.0, 1.3 currently available. Please note: These revisions are not to be confused with the USB standards 2.0, 3.0 etc. The most basic features are independent in regard to the revisions. The most recent revision 3.0 adds some features like authentication. InLine cables named USB 3.1 PD 2.0 are compliant to the Power Delivery revision standard 2.0 and are also compliant to USB 3.1 featuring data rates of SuperSpeed+.
USB Power Delivery 3.0 is backward compatible to Rev. 2.0. So hosts, devices and cables of revision 3.0 will work in combination with devices featuring revision 2.0. USB usually does not specify for this very reason, which PD revision is supported by the product. They are simply PD products
USB Type C, Power Delivery, image transfer, data rate? What will my USB connection be capable of? Please note these icons!