Port controllers, transceivers, and special dc/dc converters now simplify the task of adding USB Type-C functions.
DANIEL LEIH, MICROCHIP TECHNOLOGY INC.
CONSIDER THE VIRTUES of the USB-C connector. In addition to its 10 Gbit/sec (Gbps) bandwidth and Alt Mode video capabilities, two attributes, in particular, make this form factor incredibly valuable: a reversible plug and intelligent, high-power capability. The value of the reversible plug is obvious: Finally, we can all simply plug in our devices without having to flip the plug over (often twice). It is the intelligent power aspect, however, that makes the USB-C connector so useful.
USB has always had the ability to provide power, as long as 5 V and less than 1.5 A was enough. That limited the previous Type-A and Type-B form factors to power small electronic devices like thumb drives or keyboards, or to trickle-charge devices such as cell phones. With USB-C comes a new standard, Power Delivery (PD), which allows the source and the sink to negotiate power up to 100 W at voltage levels from 5 – 20 V. This means that a little USB-C plug can energize many more products than previously possible, including external storage devices, phones, PCs, power tools, medical devices and countless others. With 100 W on tap, just about anything you can fit in your electric car can be charged with a USB-C port (but not the car itself – sorry).
The PC and mobile phone industries have quickly adopted USB-C. Most notably, the iPhone supports Power Delivery through the Lightning Connector, and Android phones implement the USB-C connector in most new models. Initial USB -C and Power Delivery designs were complicated, involving many external components and software configuration tools. Now, new ICs take the guesswork out of USB-C designs.
In any product design, the first step is to define the desired feature set. This is especially true in a USB-C system with Power Delivery because the number of PD features have a direct impact on the cost of the system. PD itself adds cost to the system, so the end product must benefit from the power delivery capability to justify the added expense.
USB-C is versatile and supports data types beyond those of traditional USB. Designers must keep data types in mind when selecting the appropriate USB-C components. If the product is a storage device or a battery charger, there is no need to spend money on firmware to implement Alt Mode video. Conversely, if the system is a monitor that will connect to a DisplayPort-enabled laptop, the design must include specific port controllers and components. The USB-C port elements include the PD/USB protocols, data and power, so the design will include both a USB-C Power Delivery Port Controller and analog and power components.
One of the simplest USB-C implementations is the charge-only port. In this case, the system is designed to power and/or charge the devices that connect to it. An example of this type of system is a rear-seat charger in a car, a power tool battery or a wall charger in a house.
In this example the list of major ‘Bill of Materials’ (BOM) components is relatively short:
- USB-C port controller – Negotiates the connection and power contract.
- DC/DC converter – Converts the input voltage into the Vbus voltage required by the PD contract.
- Load switch – Delivers 5 V to Vbus at plug in, connects the appropriate Vbus voltage once the PD contract is established. Sometimes combined with the dc/dc converter.
- LDO – regulates voltage to the port controller because the dc/dc may be requested to supply from 5 V – 20 V
- USB-C connector
The port controller in this example must be able to handle all of the negotiations with the connecting device. Modern standalone controllers such as those from Microchip include, at a minimum, the following features:
- USB-C connector support with connection detection and control
- USB Power Delivery 3.0 compliant MAC
- Pre-programmed Power Delivery Firmware
- Support for all standard Power Delivery profiles (15/27/45/60/100 W)
- Integration of select analog components that reduce the BOM cost and design complexity.
Examples required for connection include:
- VCONN FETs with Rp/Rd switching
- Dead battery Rd termination
- Programmable current sense for overcurrent conditions
- Voltage sense for overvoltage conditions
- Appropriate temperature support for the application
Because this is a charge-only app, it requires no other system controllers. Though some suppliers offer programmable devices, the logical choice for a charge-only design is a pre-programmed product with no software requirements. System configurations take place through simple device straps (connections to ground or Vcc). If the controller is PD 3.0-compliant, users will have access to all standard power profiles: 15 W/27 W/45 W/60 W/100 W.
The choice of dc/dc converter type mostly depends on the input voltage. The power supply must always be able to provide an output voltage from 5 to 20 Vdc for full PD compliance. A basic buck topology can usually handle a design having a 24-Vdc input or voltage greater than 20 Vdc. Lower-voltage dc or offline ac-powered systems will need alternate topologies.
Another common configuration is that of a USB-C connection behaving like a power source and handling USB 2 data. In this case, the designer provides USB 2 host support for data transfer because the product contains a microcontroller with native USB 2 support. Note that the port controller does not need any connection to the USB 2 data path. No additional components are necessary, and the USB-C port BOM is the same as the charge-only design. USB 3 could also be added by including a USB 3 mux (to enable the USB-C plug reversibility), provided the MCU/system controller supports USB 3. In this example, the use of a standalone USB-C pre-programmed port controller is also the simplest way of adding a single USB-C port to an existing product offering.
At the top of USB performance architectures is the hub-based system. The hub-based design offers the most flexibility and performance of any USB architecture while removing the burden of communications from the central processor. This type of system is common in PC docks and monitors, automotive center consoles, and in any application that needs multiple USB connections.
In a PC use-case, video signals will likely pass through the USB-C port, so the Alt Mode functions must be supported. The port controller for this use case must be capable of supporting Alt Mode functions, and the design must contain the circuitry to manage direction and interpretation of the protocol passing through the Alt Mode channels.
The use of a multi-port “SmartHub” in this system offers designers a more efficient system-level design. The designer could simply purchase a more feature-rich port controller and leave the functions separate, but the use of the controller within the hub as the port controller reduces cost and processing overhead. This is especially true in multi-port systems where coordination of data movement or power usage is important.
An evolved version of port control is increasingly prevalent as USB-C becomes more available natively within controllers and processors. All USB-C functions — such as Port Policy Management, Power Delivery, Alt Mode support and Billboard support — reside within the hub. In this architecture, the standalone port controller is replaced with a transceiver. The transceiver contains the physical layer of the USB-C interface, much in the way Ethernet networks are designed.
To support the Alt Mode function, the design includes an external crossbar mux which redirects the video data to a DP connector for display on an external monitor. To address today’s increasing concerns about data and network security, this design contains a security IC that enables secure updates to the system firmware. Highly secure devices such as Microchip’s ECC608A enable the designer to ensure the safety of code through the use of NIST, SHA-256 and HMAC hash, and AES-128 encryption, without the manufacturer, even knowing the owner’s key.
Additions to the system BOM examples above include:
- USB multi-port SmartHub – Contains controller and multiple USB connections.
- Crossbar mux – Diverts various data channels to different locations.
- DP Connector – Connects to a video display.
- Type-A connector(s)
- Type-A power source
- Security IC – Enables secure code updates to the hub.
- USB-C transceiver for each port
- DC/DC converter for each USB-C PD port
A USB SmartHub with integrated Power Delivery also enables other system-level features. Advanced systems that contain HostFlex Technology, wherein any Type-C port can become the system host, let users take over displays and output functions without regard to which port they connect to. Power Balancing functions also let a user-defined algorithm apportion some fraction of total power to various subsystems. Users can decide if power is delivered in the order of connection, based on device type, based on the number of devices connected, or via some combination of those criteria.
The enabling technology for these features is the Microchip SmartHub, which orchestrates platform-level management of all concurrent USB-C PD port connections. Microchip has demonstrated system-level features such as HostFlex, MultiHost (concurrent host capability), and power balancing on the newest line of USB 3.1 multi-port SmartHubs with integrated PD.
USB-C is the connector that finally enables multiple types of data and multiple power levels to coexist within a single connector. Advanced system features such as HostFlex and Power Balancing can be easily implemented using a SmartHub design, while basic charging circuits can be implemented with simple, strappable port controllers. Future devices will make use of higher levels of integration and will further ease implementation.
Designers need not fear the task of adding USB-C to their designs. Semiconductor companies like Microchip are now producing unique and highly capable port controllers, transceivers and companion dc/dc converters, as well as the support needed to make the design job simple and low-risk.
Microchip SmartHub IC Design Center, www.microchip.com/design-centers/usb/product-families/smarthub