Designing Type-C products based on EZ-USB™ FX3 and CX3 - KBA218460
Translation - Japanese: FX3™/CX3ベースのUSB Type-C製品の設計 - KBA218460 - Community Translated (JA)
The salient features of the USB Type-C connectors are that they are reversible and they could provide power up to 100 W. That is, the USB Type-C cable can be connected in any orientation (upside down) and that the VBUS voltage can be up to 20 V, 5 A. To achieve a reversible connection, the USB Type-C receptacle has one extra pair of all the USB data lines (SuperSpeed and Hi-Speed). The correct pair of USB data lines should be selected using a multiplexer based on the orientation in which the USB Type-C connector is inserted. The following sections describe three types of FX3/CX3 designs with USB Type-C connectors.
For more details on Type-C connectors and USB power delivery (PD), see the USB Type-C specification and the USB power delivery specification. The following sections are applicable for FX3 and CX3 families of devices.
1. FX3 Type-C Plug Design
This Type-C plug design is suitable for standard devices (for example, RAID dongles, flash drives) that require the VBUS voltage of 5 V and current not more than 3 A; such designs don’t require any USB-PD controller.
For applications with Type-C plug and FX3, a multiplexer is not required for selecting the correct pair of USB data lines because the USB host can handle the right connection. The sample schematic for FX3-based USB Type-C plug design is shown in Figure 1. A pull-down resistor (Rd) of 5.1 kΩ is required on the configuration channel (CC) line of the plug to indicate that the device is a power consumer (power sink) and requires VBUS of 5 V and not more than 3 A.
No additional power delivery controller or additional firmware implementation in FX3 is required when using a USB Type-C plug-based design because, by default, the host provides 5 V, 3 A over Type-C. If the application needs other voltages/currents, a PD controller is required. See Section 3 for more details.
Figure 1. FX3 Type-C plug design schematic
2.FX3 Type-C Receptacle Design
Devices such as camera modules, docks, and monitors are designed with Type-C receptacles. They are connected to the USB host through a Type-C cable.
For applications that use the USB Type-C receptacle, a multiplexer is required to select the correct pair of USB SuperSpeed (SS) data lines to communicate with the USB host depending on the Type-C connector orientation. A Type-C SS mux, which automatically detects the orientation using the CC lines from the connector and routes the proper SS differential TX and RX lines to FX3/CX3, can be used for this purpose.
The USB Type-C specification, by default, without USB power delivery (PD), supports transmitting up to 5 V, 3 A of power through VBUS. For applications that do not require more than 3 A current at 5 V, the USB PD controller chip is not required. The sample schematic of the USB connections with USB Type-C receptacle and multiplexer is shown in Figure 2.
- In Figure 2, the pull-down resistors on CC lines are marked DNP because these are implemented internally by the mux (PI5USB30213AXEAEX). If a different mux that does not internally pull down the CC lines is used in the design, CC lines should be pulled down externally.
- For mux-only designs that do not have a redriver inside, consider the following additional guidelines:
a. AC capacitors are required between the Type-C connector and the mux input on TX lines.
b. AC capacitors are not required between the FX3 controller and the mux output.
A sample schematic for a USB Type-C receptacle + mux-only design is shown in Figure 2.
Figure 2. FX3 Type-C receptacle design schematic
- In Figure 3, the pull-down resistors are placed externally because the redriver (PI2EQX638XUBEX) does not have internall pull down.
- For a mux + redriver design or for those multiplexers that have redrives inside, consider the following additional guidelines:
a. AC capacitors are required between the Type-C connector and the mux input of the redriver on both TX and RX lines.
b. AC capacitors are required between the FX3 controller and the mux output of the redriver-only design on the TX lines.
A sample schematic for the USB Type-C receptacle + redriver design is shown in Figure 3.
Figure 3. FX3 Type-C receptacle + redriver design
3. FX3 Type-C receptacle design with PD controller
For applications that require different voltages/currents other than 5 V, 3 A, a USB PD controller is necessary to negotiate the power numbers with the Type-C PD host. The PD controller chip controls the multiplexer/switch matrix and selects the correct pair of USB SS data lines. The PD controller takes care of the USB Type‑C and PD-related requests.