USB cables have four pins – Vbus, D-, D+, and GND. The Vbus pin provides power to a connected USB device. So the answer is – the Vbus pin on a USB cable provides power.
What is USB?
USB stands for Universal Serial Bus. It is an industry standard interface that defines cables, connectors and communication protocols used for connection, communication and power supply between computers, peripherals and other computers.
The USB interface allows easy plug-and-play connectivity between devices from different manufacturers. USB has become the standard connection method for computer peripherals such as mice, keyboards, printers, cameras, storage devices etc.
History of USB
USB was developed in the mid-1990s by a group of 7 companies – Compaq, DEC, IBM, Intel, Microsoft, NEC and Nortel. The goal was to standardize the connection of computer peripherals and avoid the proliferation of different connectors and protocols.
USB 1.0 was released in 1996. It provided data rates up to 12 Mbps. USB 1.1 was released in 1998 introducing support for interrupt data transfers.
USB 2.0 was released in 2000. It introduced higher maximum signaling rate of 480 Mbps. USB 3.0 released in 2008 increased speeds up to 5 Gbps. The latest version USB 3.2 released in 2017 supports data rates up to 20 Gbps.
Over the years, USB has become ubiquitous. It has replaced many varieties of serial and parallel ports as the primary means of connecting peripherals to computers.
USB Cables and Connectors
USB connectors have evolved over the years along with the USB standards:
USB 1.x Connectors:
- USB-A – Rectangular USB host connector commonly found on computers, hubs etc.
- USB-B – Square shaped USB device connector commonly used on USB printers, scanners etc.
USB 2.0 Connectors:
- Mini-A, Mini-AB, Mini-B – Smaller versions of USB-A and USB-B connectors used in smaller devices like cameras, phones etc.
USB 3.x Connectors:
- USB 3.0 Micro-B SuperSpeed – Supports USB 3.x speeds in a Micro-B form factor.
- USB Type C – Reversible plug connector that supports USB 3.x and Thunderbolt 3. Being increasingly adopted.
The most commonly used USB connectors are:
- USB-A – For hosts/upstream ports
- USB-B – For devices/downstream ports
- USB-C – Reversible connector for both hosts and devices
USB cables have four conductors – a power line (VBus), a ground line (GND), and a twisted pair of data lines (D+ and D-). The USB spec requires a cable voltage of 5V +/- 5%. Thicker cables are used to minimize power drop over long cable lengths.
USB Cable Pinout
The four pins of a USB cable are:
| Pin | Name | Description |
|---|---|---|
| 1 | VBus | +5V Power |
| 2 | D- | USB Data – |
| 3 | D+ | USB Data + |
| 4 | GND | Ground |
So in summary:
- VBus – Provides power to the USB device
- D- and D+ – Twisted pair used for USB data transfer
- GND – Ground reference for power return
USB Power Delivery
The USB specifications limit standard downstream USB ports to 5V 500mA (2.5W). High power devices like external storage enclosures, printers etc may require more power.
For this, the USB Battery Charging specification released in 2010 defined configurable charging ports that can provide higher currents up to 1.5A (7.5W).
USB Power Delivery introduced in 2012 further expanded this by allowing much higher power of up to 100W over a USB cable. This is achieved by negotiating increased voltages up to 20V between the host and device.
USB-C connectors and cables designed for USB Power Delivery can dynamically negotiate these different voltage/current profiles to either deliver or receive power efficiently.
Uses of USB Power
The most common uses of the 5V power from a USB port/cable are:
- Powering USB peripheral devices like flash drives, keyboards, mice etc.
- Charging smartphones, tablets, cameras and other mobile devices
- Providing power for external USB hubs and accessories
- Cooling small USB fans
- Powering small lamps, LED lights etc.
With higher power delivery over USB-C, more power hungry uses are:
- Charging laptops
- Powering monitors, TVs and other display devices
- Running external GPUs and docking stations
- Charging high capacity power banks
- Powering peripherals like external hard drives, printers etc.
USB Power Delivery even enables some computers and laptops to be powered entirely over USB-C at up to 100W.
Conclusion
To conclude:
- USB cables have four pins – Vbus, D-, D+, and GND.
- The Vbus pin provides +5V power to USB devices.
- USB Power Delivery allows negotiating higher voltages up to 20V for power delivery up to 100W.
- Common uses of USB power include charging mobile devices, powering peripherals, lights, fans etc.
- So the Vbus pin on a USB cable is responsible for supplying power to connected USB devices.