Making the most of industrial USB Type-C connectivity
03 November 2016
USB allows flexible, low cost connectivity but there are challenges for using the technology in industrial environments.
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This article looks at the techniques for implementing USB in industrial applications, with the different use case and technology approaches that apply to USB2.0 and 3.0 and USB Type-C connections.
The world of industrial connectivity is going through significant changes. USB has dominated the PC industry for two decades, with the rectangular Type A socket found on host devices such as desktops and laptop computers and the squarer Type B socket used on larger peripherals, like printers, scanners and test equipment. Smaller peripherals, e.g. a mouse or flash drive, connect to hosts with Type A plugs while a Type B to Type A cable would normally be used to connect larger peripherals to their hosts.
Type A and Type B connectors have increasingly been adopted in industrial applications for their ease of design and suitability for high volume production. They may simply be used for connections that previously used a serial cable or for interfaces for peripherals such wireless modules or additional memory. Other uses include providing a port for diagnostics or to allow a memory stick to be used to upgrade firmware.
These connectors have been used with the USB2 and USB3 Full Speed and SuperSpeed protocols, moving from 480Mbit/s through to 5Gbit/s, and have been widely adopted in industrial equipment designs, largely because they have been a standard connector on embedded PC boards.
Now the 24pin Type C connector and a new protocol, USB3.1, are set to shake up the market. The Type C connector is reversible so there is no longer the challenge of inserting the cable the correct way round, and is designed to support higher power ratings up to 100W. However, the 3.1 protocol also provides detection capabilities and data rates up to 10Gbit/s.
This is also opening up the opportunity for new applications where industrial or medical displays act as the power and data hub for equipment, with the USB Type-C cables supporting both higher power peripherals and delivering high speed data over a range of other protocols such as I2C. This gives the system designer much more flexibility for moving data around.
As USB Type-C connectors become standard on PC motherboards, so they will appear on single board computers for industrial applications, providing the same advantages to industrial designers. The higher speed supported by the connector and the protocol also allows HD video streams to be easily transferred for machine vision applications.
Connector suppliers are delivering Type C connectors that handle the higher power and are rugged enough for industrial applications, while semiconductor suppliers are providing USB and power controllers small enough to fit into those connectors.
A key element of the Type C connector design is the USB Power Delivery Specification, which enables the maximum functionality of USB by providing more flexible power delivery along with data over a single cable.
This provides an increase in power levels from the existing USB standards up to 100W with bidirectional power so that the product with the power (whether Host or Peripheral) can provide the power. The protocol also allows each device to take only the power it requires, and to get more power when required for a given application. The specification is not just about the connector, as an I2C interface can also be added using the PD specification.
The Transport Interface specification defines a communication protocol for use over I2C or other peripheral interfaces. It uses the structure defined in the USB Power Delivery Specification and extends it for use on other buses. By way of a simple example, this specification enables a standardised communication protocol between a USB Power Delivery Controller and a system controller as well as providing control over power management peripherals such as a DC-DC converter.
However, there are different ways of implementing the technology.
The USB Type-C connectors from TE Connectivity provide one solution to deliver data up to 10 Gbit/s, power up to 100 watts, and audio/video input in a single small form-factor connection.
The USB Type-C connector features a reversible mating interface where the receptacle is designed to accept a plug in any direction, enabling easy, reliable mating. This connector supports a variety of different protocols, and with the use of adaptors, it is backwards compatible to HDMI, VGA, DisplayPort, and other types of connections from the single USB Type-C port. A distinctive electromagnetic interference (EMI) design on the back of the stainless steel shell helps eliminate unwanted EMI leakage, as well as providing enhanced retention for better performance in rugged industrial environments.
As the connector can be connected either way round, a connection detection capability has been added to the connectors at the Vconn pin. This determines the orientation of the connectors and so determines which pins will be used for the upstream and downstream facing ports (UFP and DFP) as well as the high power pins. This means some pins need to be powered up first.
The connector supports USB 2.0 (480 Mbps), USB 3.1 Gen 1 (5 Gbit/s) and USB 3.1 Gen 2 (10 Gbit/s) and is specifically aimed at factory automation and industrial machinery as well as medical devices, power packs and chargers, and automotive infotainment system designs with a temperature rating of -30°C to 85°C. It has a voltage rating of 30V and current rating of 5A on the Vbus pins, 6.25A on the ground pins and 1.25A on the Vconn pins. The signal pins support a maximum current of 0.25A.
Amphenol has seen USB evolve from a data interface capable of supplying limited power to a primary provider of power with a data interface. These additional capabilities can be added using the latest semiconductor devices, such as the controller from Cypress Semiconductor shown in Figure 3, integrated into the connector shell.
Fairchild Semiconductor’s FUSB301ATMX device is an example of a flexible, thin client solution for USB Type-C control. This targets system designers looking to implement the DFP and UFP elements of the USB Type-C connector without the USB-PD power capability while also providing software flexibility for multiple platform support through the I2C connection. The FUSB301 performs USB Type-C detection including attach and orientation by automating the VBUS threshold detection as well as the various charging current levels.
Some chip developers are adding more processing capability. The CCG2 from Cypress Semiconductor is the company’s second generation controller for Type C connectors. It uses a 48MHz ARM Cortex M0 32bit processor core to configure the connection, with a separate block for the Vconn detection of the pins on insertion, as well as integrating the transceiver, termination resistors and ±8kV system level electrostatic discharge protection. There are up to 14 GPIO pins on the QFN package, 7 GPIOs on the smaller DFN package and 9 GPIOs on the chip scale WLCSP package that measures just 3.3mm2. It provides a complete solution for passive Electronically Marked Cable Assembly (EMCA) cables, active EMCA cables, USB Type-C notebooks, power adapters, monitors, docks and cable adapters such as dongles.
The system-on-chip design adds integrated timers, counters and pulse-width modulators as well as two Serial Communication Blocks (SCBs) that are configurable to I2C, SPI or UART modes to extend the PD power specification.
The process of connecting with a Type-C device is demonstrated by the TPS65982 from Texas Instruments. This single chip controller is divided into six main sections: the USB-PD controller, the cable plug and orientation detection circuitry, the port power switches, the port data multiplexer, the power management circuitry, and the digital core.
The USB-PD controller provides the physical layer (PHY) functionality of the USB-PD protocol, with the data output through either the C_CC1 pin or the C_CC2 pin, depending on the orientation of the connector. The cable plug and orientation detection analogue circuitry automatically detects a USB Type-C cable plug insertion and also automatically detects the cable orientation.
On cable detection, the TPS65982 communicates over the CC wire using the USB PD protocol. When cable detection and USB PD negotiation are complete, the TPS65982 enables the appropriate power path and configures alternate mode settings for internal and (optional) external multiplexers.
The mixed-signal front end on the CC pins advertises a 500 mA supply as default as well as 1.5 A and 3 A options for Type-C power sources. It detects a plug being inserted or removed and determines the USB Type-C cable orientation, and autonomously negotiates USB PD contracts using a specified bi-phase marked coding (BMC) protocol. This is a self clocking scheme that can handle either synchronous or asynchronous data and depends on phase-inversions to identify bits.
The port power switch provides up to 3 A downstream at 5 V for legacy Type A and B connectors and for Type-C power connections. An additional bi-directional switch path provides USB PD power up to 3 A at a maximum of 20 V as either a source at the host, a sink at the end device or a source-sink.
The port data multiplexer passes data to or from the top or bottom D+/D– signal pair at the port for USB 2.0 HS and has a USB 2.0 Low Speed Endpoint. A Sideband-Use (SBU) signal pair is used for alternative connection protocols such as DisplayPort or Thunderbolt but still within the same connector.
The power management circuitry uses VBUS to start up and negotiate power for a dead-battery or no-battery condition.
The digital core provides the engine for receiving, processing, and sending all USB-PD packets as well as handling control of all other TPS65982 functionality. A small portion of the digital core contains the boot code in non-volatile memory for initialising the device and loading a larger, configurable portion of application code into volatile memory in the digital core. This uses information provided by the analogue-to-digital converter ADC to read the status of general purpose inputs and trigger events, and controls general outputs which are configurable as push-pull or open-drain types with integrated pull-up or pull-down resistors that can operate tied to either a 1.8 V or 3.3 V rail.
Just as USB Type A and B connectors and the USB2.0 and 3.0 protocols have become a key part of the design of industrial and medical equipment, so the advantages of Type C and USB3.1 will drive the technology into these applications even more effectively. Although the reversibility of the connector requires more complex pin detection and allocation, improvements in the silicon controllers allow this complexity to be easily integrated into the new connector shells.
While the higher data rate is not a large driver of new designs, it also helps to add higher resolution displays to equipment to make user interfaces more effective and open up applications in machine vision.
However the key factor is that the new Type C connectors with their higher power delivery to open up new ways of designing industrial equipment, allowing displays to be USB hubs and allowing developers to easily add new higher power and higher performance peripherals to a system without having to worry about power delivery and management. This can significantly reduce the complexity of the system design and reduce the cost and development time.
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