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Unraveling the hype around USB C connectors
USB C connector type aims to finally bring the “Universal” to Universal Serial Bus.
You’ve probably noticed the latest USB connector popping up on your new electronics devices and thought “Oh, Great! Now I need new cables and chargers… again.”
Why do designers create new cables with different connectors?
In the past, new USB connectors were created to serve higher speeds, smaller connector area, and more power. The driver is similar for USB C, but this time the designers had much more foresight and made some design improvements too.
With this perspective, let’s look at some of the factors to keep in mind while choosing the right design partner for you:
A brief History:
Before the days of USB, computer cabling was a disaster: Different peripherals had different cables and connectors (often very bulky), many required special software installations and reboots, and each computer port could only handle one peripheral.
USB elegantly solved all these problems: one connector type on a light cable with plug-and-play, hot-swapping, and expandability of up to 127 devices on a single bus.
|Speed & Transfer Rate
|USB 1.0 with USB A connector
|1.56 Mbps, 100mA
|USB 1.1 with USB A connector
|12 Mbps, 100mA
|USB 2.0 with USB A connector
|480 Mbps, 500mA
|USB 3.0 with USB 3 connector
|5 Gbps, 900mA
|USB 3.1 with USB 3 connector
|10 Gbps, 1.5A
|USB 3.1 with USB C connector
|10 Gbps, 3A
|USB 3.2 with USB C connector
|20 Gbps, 5A
|USB 4.0 with USB C connector
|40 Gbps, 5A
Some of the design improvements with USB C include:
1. A reversible connector: There is no need to fumble around for the correct orientation. Just pop it in the right way the first time.
2. A reversible cable: Both ends are the same! Again, no need to fumble around.
3. Higher power capability: Up to 250W of power - enough for most consumer electronics, so you’ll see these connectors on just about every electronic device, from laptops to cell phones to set top boxes, tv’s, and lamps.
4. Higher Speeds: Up to 40Gbps for USB 4 and Thunderbolt
5. Alternate modes: USC C cables can also be used for non-USB purposes such as HDMI, Thunderbolt, and DisplayPort. The aim is to reduce the number of different cables one needs around the home or office, with the ability to re-purpose them in the future.
6. Backward compatibility: With adapters, you can use the USB C cable for any previous type of USB.
Figure 1: Type of USB connectors
USB C is being promoted as the universal solution for electronics/connectivity going forward. This push comes from the European Union driven by their superior environmental policies. In the past, every electronic device came with its own power supply (whether built-in, or as a separate unique part). The power supply would be chucked into the garbage at the end of a product’s life. In recent years we’ve seen USB A chargers start to power and charge a wide range of electronics, so many devices no longer come packaged with a new charger or voltage adapter – reducing the amount of electronic clutter and waste. We should see this trend expand with USB C’s higher power and speed capabilities.
USB C adds a feature called “Power Delivery” (PD) that allows the connected devices to discuss their power roles and capabilities/ needs. For example, a cell phone’s USB C connector could be used to charge the phone’s battery (when the cell phone acts as a “sink”) but might also be used to charge another device such as a laptop or a wearable device (cell phone acts as a “source” in this case).
The electronics designer needs to determine which Power Delivery capabilities to support in their designs when they adopt the USB C standard, if any, and integrate the hardware to support it - such as PD controllers and/ or switching power regulators.
Reversibility - Data Switching:
High data rates are achieved using dedicated unidirectional data lines. But those lines can be mis-connected because the USB C connector is reversible. The device must accommodate this using a high-speed data switch: It detects the connector’s orientation, then directs data flow accordingly.
USB C Connectors:
Despite their smaller size, USB C connectors have 24 connections (compared 4 on USB 2 or 9 on USB 3) packed closely together. Routing these connections necessitates multi-layered circuit boards with thin traces/ clearances and careful impedance control - especially for high- speed applications.
Another challenge is that most of the USB C connectors on the market are surface-mount (as opposed to through-hole) - leading to a weak mechanical connection, where it is likely to encounter high mechanical strain. Proper mechanical support and/ or through-hole supports need to be implemented and tested, with careful attention to the manufacturing/ soldering process to ensure these connectors don’t break off.
With one “standard” cable covering so many different applications, there is bound to be some confusion, improper connections, and frustration. For example, Thunderbolt and USB C use the same connectors, but they are not always compatible. Yes, there are standard symbols for indicating device capabilities - but device size often limits their visibility (if they’re used at all).
Electronics Designers and Engineers must consider all the ways their USB C connector will get used and abused, and help the end-user understand the capabilities and limitations of their devices - despite their “Universal” connector.