Lattice – Implementing USB Type-C Cable Detection and Power Delivery Negotiation

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By: Gordon Hands, Director of Marketing, Lattice Semiconductor

20 years after the first Universal Serial Bus (USB 1.0) helped bring interoperability to a fragmented electronics industry, the Type-C interface specification updates USB to meet the needs of 21st century electronics and promises to once again change the way computers, consumer electronics and mobile devices connect and interact with each other. The slim, rugged and reversible Type-C connector extends the capabilities introduced by the USB 3.1 SuperSpeed+ specification by using two channels to provide a total bandwidth of over 20Gbps, opening the door to reducing data transfer time for large files such as HD movies and 3D images by up to half. Thanks to USB Type-C’s high power capabilities, it can supply up to 100W to allow fast battery charging and the provision of power to larger devices such as laptops, monitors and TVs. Type-C also introduces several other unique features, including new alternate modes which enable the USB connector and cable to carry other data such as DP, VGA, MHL and HDMI video.

Type-C in a Nutshell
The Type-C USB interface derives its name from the Type-C connector, selected by the USB Implementers Forum (USB-IF) as a sturdier, easier-to-use alternative to the Micro-B connector used in many of today’s mobile devices. The non-polarized 24-pin connector’s mechanical design reflects the lessons learned from the Micro-B’s checkered service history and is rated for 10,000 mate/de-mate cycles. In addition, users no longer need to worry about “which end goes up” because the Type-C connector allows mating in either orientation. And, unlike the majority of other USB cables, Type-C cables use the same male connector on both ends (see Figure 1).

Figure 1: USB Type-C connector

Figure 1: USB Type-C connector

Type-C Signals
The Type-C connector’s 24-pins are arranged within a symmetrical shell which allows it to mate in either a ”normal” or an ”inverted“ orientation. While convenient for the user, it does mean that only some of the connections it makes are ”symmetric“ i.e. orientation-independent, while the others require some level of accommodation from the USB devices (see Figure 2).

Figure 2: Type-C connector details

Figure 2: Type-C connector details

D+/D-: These pins provide a signal path for USB2 signals when a USB3 interface isn’t available.

Vbus/GND: These pins can be used to deliver up to 100W of power. Until prior versions of USB, VBUS can be increased from the default 5V to up to 20V.

Tx1/2 Rx1/2: Provide for up to 2-channels of SuperSpeed+ data links providing a bandwidth of up to 20Gbps in both directions.

CC1/CC2: Configuration channel signals used in the discovery, configuration and management of connections. Note that only one of these signals is used as a configuration channel. The other is repurposed as a power supply for active components that may be present in the cable.

SBU1 and 2: The side band use signals are intended to carry non-USB signals. They are used in analog audio mode and may be used by alternate modes.

Implementation Challenges for Type-C Applications
At present, adding a Type-C USB interface to a new design requires developers to supplement the capabilities of the chips they intend to use in their systems because neither the PHY devices, MCUs nor Application Processors (APs) used in today’s systems include the hardware needed to support several critical functions required to unlock the power of USB Type-C interfaces. These essential building blocks include Cable Detect (CD) and Power Delivery (PD) functions.

CD in Detail
USB Type-C Upstream Facing Ports (UFP, typically a device in older USB terminology) apply 5.1K pull-down resistors to the CC pins in their Type-C receptacle. Downstream Facing Ports (DFP, typically a host in older USB terminology) apply pull-up resistors to the CC pins in their Type-C receptacle. The value of pull-up resistors they apply advertises the amount of current that can be drawn unless a PD contract is established. Cables only have one CC conductor. The other signal corresponding to CC in the receptacle is VCON. Cables apply a 1K pull-down resistor to VCON at each end of the cable. The CD function uses the voltage on the CC lines to determine if a cable is attached, the orientation of the cable and the type of device attached to the other end of the cable (see Figure 3).

Figure 3: Cable configuration overview

Figure 3: Cable configuration overview

PD in More Detail
PD communication allows both sides of the link to communicate and determine the voltage and current to be provided on VBUS, swap data and power roles, agree to use alternate modes for functions such as video and implement Vendor Defined Messages (VDM). The PD communication stack has 4 levels. The physical layer sends data at a nominal 300KHz on the CC line. Data is sent using Bi-phase Mark Coding (BMC) to provide a clock transition for each bit of data, making clock recovery simple. 4b5b encoding and CRC are also used. Above the physical layer is the protocol layer which defines the communication format. Above the protocol layer is a policy engine layer. The policy engine layer defines how a device will negotiate a PD contract and other capabilities. The policy engine’s behavior can be modified by the final layer, the device policy manager layer (see Figure 4).

Figure 4: Power deliver communication stack

Figure 4: Power deliver communication stack

Lattice USB Type-C Solutions
Lattice provides 3 solutions that enable designers to implement the CD, PD and VDM functions required to unlock the power of USB Type-C. These solutions use state machine logic to implement the CD and physical and protocol layers of the PD function. This approach yields low power consumption while meeting the tight timing required. A mix of microcontroller and logic is used to implement the PD policy engine and device policy manager layers.

Lattice CD/PD for Chargers Solution
The LIF-UC110-SG48I provides a standalone solution that implements the CD and PD functions that are required to implement Type-C in charging ports and travel adapters (see Figure 5). The device is supplied in a 48-pin QFN package to match the PCB technology most normally used in this type of equipment.

Figure 5: Using FPGAs to implement CD/PD functions for chargers

Figure 5: Using FPGAs to implement CD/PD functions for chargers

Lattice CD/PD-PHY
The LIF-UC120-CM36I and LIF-UC120-SWG36I implement the timing critical CD and PD physical and protocol layer functions, allowing a microcontroller to be used to implement the policy engine and device policy management layers (see Figure 6). The solution is intended for use in handheld devices and other space constrained applications. It is provided in 0.35mm and 0.4mm BGA packaging with dimensions as small as 2.08 x 2.08mm.

Figure 6: CD/PD lite for mobile devices

Figure 6: CD/PD lite for mobile devices

Lattice CD/PD
The LIF-UC140-CM81I provides a standalone solution that implements the CD and PD functions required within a USB device or host. A serial interface (I2C or SPI) allows a system microcontroller to read the connect status and modify the behavior of the device policy manager if desired (see Figure 7). Initially this solution is available in a 4 x 4mm 0.4mm BGA package. Additional larger pitch packages are also under investigation.

Figure 7: CD/PD for mobile devices

Figure 7: CD/PD for mobile devices

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