USB-C for data transfer and fast charging

Everyone is charging every day, all the time, on multiple devices, everywhere you look. As more designs opt to use USB Type-C® connections instead of USB Type-A, this type of connection needs to be thoroughly understood by the design engineer. USB Type-C has some significant advantages, with some complications. The launch of USB Type-C adds more capabilities to these connections than just charging. Data is also being exchanged at very high speeds.

Although the designations for various versions and types of USB-C can be confusing, understanding that USB-C is a game changer is essential for several reasons outlined in this article.

The USB Revolution

Since its introduction in 1996, USB has revolutionized the way we connect our computers to peripheral devices, replacing a plethora of outdated serial and parallel ports. But that was only the beginning. With the launch of USB 2.0 in 2000, speeds reached an impressive 480Mbps, and power capacities were increased to 500mA, making it possible to charge cell phones and other devices.

The improvements don’t stop there. USB 3.0, or USB 3.1 Gen 1, can handle data speeds of up to 10Gbps, while USB 3.1 Gen 2 doubles this to an impressive 20Gbps. The latest USB-C connectors, introduced in 2014 (Figure 1), are rapidly taking over the world, and with a recent EU requirement that they be used in chargers and devices, it’s clear that USB-C is the way of the future. But with different formats and revision levels, design engineers must be careful to ensure compatibility.

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USB-C connection configuration

A USB-C connection includes a configuration channel (CC) (Figure 2) which is used when a device is connected to determine the (inverted) orientation of the cable and establish a power supply “contract” passively or actively between the source and the load (and the cable, as we shall see). The load (downstream port) can detect the capacity of the source by sensing the value of a resistance presented by the source. Table 1 below shows the various possibilities.

When a USB-C cable is first connected, the device (load) end checks a resistor divider connected on both sides of the host and the device using the DC connector pins (see Figure 2). This divider has three levels and indicates whether the host is basic with 5V/0.5A or is capable of a little more at 1.5A or 3.0A. If the appropriate level is not found, the system will remain at the lower data and power levels, but will continue operations.

The basic interpretation of the DC line can increase the available power to 3.0A, but cannot raise the voltage above 5V. If the host and load start talking over the digital lines (D+ and D-), the connection can be upgraded to use PD multi-voltage operation.

USB for Power Transfer

While USB was only a data carrier with limited power capabilities in the past, the latest versions offer significant power capabilities. USB PD describes the power delivery protocol that operates over this interface. USB source-to-charge communication is multi-layered. USB PD is a specific version that emphasizes power delivery and often has data communication. PD communicates power capabilities and needs between the source and the load.

The USB-C Power Delivery (PD) standard allows the voltage to be 5, 9, 15 or 20V at power levels of up to 100W (Table 1). The current is a maximum of 5A, but a voltage of 5, 9, 15 or 20V allows much more power. “Fully featured” USB-C PD cables have a chip in their cable connector body called a channel or port configuration controller. These chips produce an electronic marker that tells the other end which power it can send and receive. Cables with a transmission current of 3A or below do not need a channel configuration chip.

PD messages are transmitted in 196-bit blocks at a frequency of 300KHz +/- 10% over the CC line. At the end of the packet, a 32-bit CRC is sent, followed by a 4-bit end-of-packet (EOP) token that completes the message.

In a PD configuration, a chip in each cable connector detects the type of power connection at both ends and adjusts the voltage supply. The device is powered/charged and can request intermediate voltages between 5V and the maximum fixed voltage available from the charger.

USB-C PD cables deserve some caution. “Basic” cables may not meet the requirements for wire size or USB signaling, so check the specifications. If your power supply is capable and you connect everything correctly, but you’re not getting the power level or signal speed, which is often difficult to determine, it’s likely due to the cable.

Advantages of USB PD

Power transmission via USB PD offers several advantages. One of the main benefits is the availability of higher energy, which is sufficient to power laptops or monitors and quickly charge compatible smartphones. The charging process can be managed by the phone, which can instruct the charger to slow down or speed up depending on the current requirement. USB PD is also highly versatile, accommodating a wide range of devices, from smartwatches to laptops. In addition, wall power adapters (Figure 3) can now safely charge almost any device with high efficiency and optimized rates, simplifying the hardware and reducing costs by being single-direction from the adapter.

Brands

In 2021, the USB Implementers Forum (USB-IF) released updated power rating logos for certified USB Type-C cables in order to specify the power capabilities of USB-C cables for consumers. Certified USB Type-C cables now feature logos (Figure 4) highlighting support for 60W or 240W of power, as defined by the recently published USB Power Delivery.

The international standardization of USB performance for data and power has now been formalized in the IEC 62680 standard.

Conclusão

In conclusion, USB-C is becoming increasingly popular and has significant advantages over its predecessor, USB Type-A. USB-C connections are not just for charging, but also for data transfer, with high-speed data transfer capability. USB-C connections have a configuration channel that determines the orientation of the cable and establishes a “contract” for passive or active power delivery between the source and the load. The latest USB-C connectors can handle data speeds of up to 20Gbps, and the USB-C PD standard allows power delivery of up to 100W at power levels of up to 5A.

However, care must be taken when using USB-C PD cables, and it is important to ensure that the cables meet the requirements for wire size and USB signaling. Despite the complexity of its connections, USB-C is the way of the future.

Article written by Jim Harrison and published on the Mouser Electronics blog: USB-C for Data and Fast Charging

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(*) This post was sponsored by Mouser Electronics.