How USB Cables Have Been

USB is ever-present in consumer electronics, allowing consumers to easily interface one device to another: add external storage to a tablet; connect a smartphone to your laptop to charge the phone and while you’re at it, sync files - transfer videos from your digital camera to your computer for editing.  No training. No configuration. Just plug it in and go.

With the mechanically distinct Type-A and Type-B connectors, plugging in the cables correctly for the USB tree is easy. Connecting from the USB host downstream to the other devices are details that consumers don’t need to know.  That it can be a “string” of trees - consumers don’t need to know that either. The USB tree was designed for simplicity - from the “upstream” host to “downstream” devices, such as a USB hub with multiple Type-A ports to connect “downward” to multiple USB devices and one Type-B port to connect “upward” to the computer’s Type A port. A “normal” USB cable has a Type-A connector on one end and a Type-B connector on the other end.  (Originally, the ports were designed for the Type-A plug and the Type-A jack – which is still in use on some products.)

Type-A	Type-B	Micro-B	Type-C

And then came the smaller, symmetrical Type C cable, destined to replace Type A and Type B connectors. There is no Type D for downstream devices; Type C connects to both the upstream and the downstream devices.

How USB Cables Are Today

The Type-C cable increased the options for consumer products, such as connecting a docking station with only one cable, delivering video signals and power to the monitor with only one cable, or determining whether the laptop is receiving power or providing power.

• The USB tree is still the same, but with the reversible design, there is no mechanical difference of which end of the cable goes where.
• There are more I/O pins - more operations are possible.
• Power Delivery (PD), an optional feature for carrying more than 3A and changing voltage and power direction for powering or charging devices.

The Type-C cable also changed things for the engineer. It had been so easy for consumers to connect their electronic devices, did that need to change?

To keep it simple for the buyers, how the cables work had to change, such as adding the Configuration Channel (CC) control logic detection, which identifies which end is connected to the host and which is connected to the device. The port has two CC pins, but the cable has only one pin CC. Some of the features CC is used for:

• Determine the orientation of the cable, which enables the devices to adjust to the wiring
• Determine which is the host and which is the device
• If both items are host or both items are device, then nothing happens, minimizing the risk of damage
• Configure VBUS for USB Type-C current modes or USB Power Delivery
• Discover and configure optional Alternate and Accessory modes, such as carry non-USB video signals
• Determine which item is being charged (and which item provides power)

There are also PD controllers. This is important as some items are Dual-Role Power – can either provide or receive power, depending on which products are connected together. Many features add many options, and many technical complications.

How to test and analyze these features? How to verify compliance? Look into the Total Phase USB Power Delivery Analyzer and the Advanced Cable Tester v2. Have any questions? Contact sales@totalphase.com.