Have you noticed USB Type-C connectors on the latest laptops and mobile electronics? In addition to having a reversible connector, closer inspection will reveal that USB Type C connectors are replacing many specialized connectors for power, display, and peripheral connectivity. The flexibility of this new interface standard is revolutionizing product design as a few small form-factor ports can now support USB 2, USB 3, power, many legacy ports, and even newer interfaces such as HDMI and DisplayPort.
USB Type-C is the latest specification to be released by the USB Implementers Forum. While the initial USB cable design was intended to replace certain types of connectors on legacy PCs, USB Type-C has moved beyond peripheral attachment and is designed to allow a single-cable “world”. It is no longer necessary to have separate power cables, display cables, and traditional USB cables. USB Type-C replaces all of these and more, and can even handle multiple functions over the same cable (like powering your laptop over the cable you’re using to connect to an external display!)
Some of the features enabled by this new connector include:
- Small form factor with enhanced mechanical robustness: The Type-C port is only 3mm tall and has been designed to offer the same level of mechanical attachment to circuit boards as legacy Type-A connectors.
- Reversible port: The USB connector is now the same on both ends of the cable, and the connector is mirrored so that it can be plugged in any orientation.
- Support for the latest USB Power Delivery (PD) specifications that allow peripheral devices to supply power to a laptop or mobile device.
- Data rates up to 40Gbps can be achieved on the same connector that powers several devices.
- Full support of USB 3.1 protocol for high speed data transfer to peripheral devices.
- DisplayPort replacement: Two 4k displays can be connected via a single port (more with compression), or one 4k display can be while also supporting USB 3 SuperSpeed connectivity.
- HDMI interface is also supported for connectivity to media devices such as TVs or projectors.
- PCIe and Thunderbolt functional extensions are also supported, enabling unique opportunities for externally installed graphics cards or high speed data storage.
Due to the flexibility of USB Type-C, the complexity and pin count of the interface has increased greatly over legacy USB ports (see Figure 1). Several major features enable this flexibility: First, the center D+ and D- pins cover legacy USB2 features. The Control Channel pin (CC) is used for cable rotation detect and service negotiation between connected devices. Four VBUS and GND pins supply the necessary current capacity for high power USB Power Delivery (USB PD), and Sideband Use (SBU) pins supply sideband communications for certain alternate mode interface protocols. Finally, the TX and RX pairs supply high bandwidth communications for USB3, DisplayPort, PCIe, and other high speed interfaces.
Figure 1: USB Type-C pin map (Credit USB Implementers Forum)
USB Power Delivery is one of the most important options to consider during product design, as the interface can support downstream 5 Volt operation to USB2 and USB 3.1 specifications (500mA/900mA), USB Battery Charging Spec (1.5A), and an additional 5V 3A profile. It also supports 5V - 20V operation at up to 5A with directional control, depending on the class of the interface. Directional control allows an attached device to either source or sink power, thereby enabling flexible power delivery solutions that weren’t available until the Type-C port was introduced. Overall maximum ratings are limited to 5A or 100W in order to comply with international product safety requirements for Limited Power Source devices. Since not all devices need to support all of these modes, it is important to select the appropriate power profiles & choose power delivery components accordingly.
During connection, a resistance to ground is first detected on the CC pin. If the device at either end of the cable can function as a Downstream Facing Port (DFP), it then supplies 5V across the VBUS and GND pins, which enables normal operation of the attached device. The CC signal is then used to detect cable rotation and configure the TX and RX pair multiplexers at both ends of the cable accordingly. Once this occurs, the interface controllers on either end of the cable determine which will be the Host and which acts as an attached device. In the case of two dual-role devices, this is determined randomly. Power delivery is then negotiated and if alternate power or reversed roles are necessary, the change is made and operation on the VBUS pins transitions to the newly negotiated mode. Finally, alternate mode functional extensions such as DisplayPort or PCIe are enabled; these connections are negotiated on the Side Band Use (SBU) pins.
On a full-featured port, many specialized components are necessary in order to achieve full functionality. A common implementation method is a Type-C interface controller and power switch, augmented by a separate high speed multiplexer. The controller handles USB2 communications and port setup, and configures the multiplexer to allow the appropriate data to flow. TI has two excellent examples of port and Power Delivery controllers in their TPS65982 and TPS65986 devices. The TPS65982 can be configured as an Upstream Facing Port (UFP), Downstream Facing Port (DFP), or Dual-Role Port (DRP) and provides cable plug detection, port setup, and PD power path negotiation and setup with alternate mode power support of 5-20V@5A. It also negotiates alternate mode functional extensions (DisplayPort, PCIe, etc.) and provides configuration for internal and optional external multiplexers. The cost reduced TPS65986 offers an identical feature set, but only supports alternate power at 5-20V/3A and it cannot negotiate or configure functional extensions. For the high speed signaling portion of the interface, a separate analog multiplexer is frequently employed to ensure the appropriate signal paths while minimizing interference from high power circuits. Because of the multiple TX and RX pairs, it is possible to use the multiplexer to connect one TX/RX pair to a USB 3 hub and the other pair to DisplayPort; Higher rate interfaces such as PCIe over Type-C may utilize all of the high speed TX/RX pairs. The TI HD3SS460 is a 4 x 6 Channel USB Type-C™ Alternate Mode multiplexer that allows simultaneous support of 5GHz USB 3.1 Gen 1 and Alternate Mode including 5.4 Gbps DisplayPort 1.2a. For ports that only need to support SuperSpeed USB 3, the TI HD3SS460 is a high speed bidirectional switch ideal for use in a bidirectional mux/de-mux application. Its -3dB bandwidth exceeds 8GHz, and it supports USB Type-C signaling up to 10 Gbps with minimal attenuation to the eye diagram and very little added jitter.
For mobile devices, peripherals, secondary Type-C ports, and other applications that do not require alternate power functional extensions, a single port controller with integrated mux can be used. The TI HD3SS3220 offers the same cable connect detection and dual-role port configuration features as the above USB Type-C controllers, but exchanges support for alternate mode power and functional extensions for an internal 10Gbps mux/de-mux switch.
Once the interface is established correctly, a USB physical layer interface is needed to translate the serial USB data to and from the USB bus interfaces on the CPU or MCU. TI’s TUSB1310A USB 3.0 transceiver simplifies system design by operating on a single clock input. It offers 5Gbps USB 3.0 SuperSpeed operation as well as a 480 Mbps USB 2 connection to ensure the device works with legacy USB hosts.
For devices utilizing DisplayPort over USB Type-C, the DisplayPort signal can be significantly degraded by the time it reaches the DisplayPort connector in an attached dock or peripheral. In these scenarios, a DisplayPort re-driver can be used in the dock to regenerate the DisplayPort signaling and ensure proper signal reception at the display device. TI’s SN75DP130 is a perfect fit for these applications as it supports 4-lane main link interface signaling at up to 5.4 Gbps per lane, and also features DP++ Dual-Mode, offering TMDS signaling for DVI and full HDMI Version 1.4a support. 2kV ESD protection is also provided, which helps ensure upstream devices are not damaged by transient events.
Where needed, additional ESD protection on other ports can be provided by TI’s TPD4E02B04 and TPD4E05U06 transient voltage suppressors. These devices feature ultra-low loading capacitance, making them ideal for super high speed interfaces. The TPD4E02B04 is ideal for regular USB links and alternate modes, including USB 3.1 Gen 2 (up to 10 Gbps) whereas the TPD4E05U06 is ideal for protecting the USB3.0 SS (5 Gbps), SBU or CC pins.
Texas Instruments has developed several USB reference designs that showcase many of the above solutions and provide insight into designing fully-functional USB Type-C devices. The first is their TIDA-00630 USB Type-C dock reference design, which is built around the TI TPS65982 USB Type-C port controller and USB-PD controller discussed above. It is powered by an external 20Vdc supply and provides 20V@3A alternate mode power delivery to the host device through the upstream facing Type-C port. It also supports DisplayPort and contains an integrated USB 3 hub. The hub connects to two Type-C data ports that each feature up to 5V/3A power output, and two USB 3 Type-A ports. One Type-A port features USB-BC battery charging at 5V/1.5A, and the remaining port offers standard USB power values (900mA for USB 3, 500mA for USB 2).
The second is for a USB Type C Power Delivery Controller and High-Speed multiplexer. This design is also built around the TPS65982, and demonstrates the full USB-PD capabilities of the part by allowing all USB-PD modes, including up to 20V/5A of upstream power delivery.
The final reference design is the TIDA-00882, a USB Type-C to SATA bridge again built around the TPS65982. This design offers an example of an external storage peripheral with USB-PD upstream power delivery of 12V/3A to a host device. A TI TUSB9261 USB to SATA bridge provides USB SuperSpeed connectivity for full SATA 3.0 Gbps operation, with USB 2 HS/FS fallback operation if connected to a USB 2 host.
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