Author: RajathB_01 Version: **
Translation - Japanese: 標準USB 3.0 / 2.0コネクタをType-Cコネクタに置き換える- KBA228953 - Community Translated (JA)
Legacy USB connectors vs USB-C
Standard USB 3.0 ports will have only one pair of {TX+/-, RX+/-, D+/-} whereas the Type-C connector/port will have two pairs of {TX+/-, RX+/-, D+/-}. The pinout is symmetric and therefore, the connector is flip-insensitive. Type-C connector also has extra pins for Type-C specific functionality like CC (configuration channel) and SBU (sideband usage). A comparison is shown in Figure 1.
Figure 1. Legacy USB Connectors Compared to Type-C
Figure 2. Pinout of Type-C Receptacle
Figure 3. Pinout of Type-C Plug
To detect attachment, orientation, and identity of the source and sink, the CC termination model is defined with the help of pull-up (Rp) and pull-down (Rd) terminations. Even though the connector is flip-insensitive, the orientation is required to know which of the SuperSpeed (SS) lanes in the receptacle is connected to the SS lanes in the plug. Initially, a Source exposes independent Rp terminations on its CC pins, and a Sink exposes independent Rd terminations on its CC pins. Figure 4 represents a valid connection of the Source-to-Sink combination of this circuit configuration.
An electronically marked cable assembly chip (EMCA marker chip) asserts Ra termination on one of the CC lines through which the Downstream Facing Port (DFP) will provide the VCONN supply to the e-marker. The other CC line will be used for source-sink negotiation (port partners).
A plug will assert either Rp or Rd (or Ra if cable plug) on any one of its CC pins (the other one is fixed as VCONN). A receptacle will assert either Rp or Rd on both the CC pins. This will aid arbitration among the CC pins.
Figure 4. Pull-Up/Pull-Down CC Model
For example, if you consider a USB 3.0 bus-powered hub (converted to a Type-C-only hub) which will have one upstream port and multiple downstream ports, the upstream port is a sink; therefore, the CC lines need to have pull-down (Rd) termination. The downstream ports will have pull-up (Rp) terminations because they source power. Table 1 lists the values of termination resistances for different values of default current advertised.
Table 1. CC Line Termination Resistances
Termination | Value for advertising the default capability | |||
DFP - 5 V, 0.9 A | DFP - 5 V, 1.5 A | DFP - 5 V, 3.0 A | UFP | |
Rp (pulled up to 3.3 V ± 5%) | 36 kΩ ± 20% | 12 kΩ ± 5% | 4.7 kΩ ± 5% | - |
Rp (pulled up to 4.75 – 5.5 V) | 56 kΩ ± 20% | 22 kΩ ± 5% | 10 kΩ ± 5% | - |
Rd | - | - | - | 5.1 kΩ |
Typical implementations with Type-C Plug and Type-C receptacle are explained in the following sections.
- Type-C Only Source with Plug:
Because it is a source, Rp will be the termination connected on the CC pin. Generally, DFPs for data (USB hosts) will not employ Type-C Plug. This configuration is used by power sources without data, i.e., mostly power adapters, mobile chargers, and power banks with captive cable. Because this configuration is not for data, USB SS lanes are left unconnected. The USB High-Speed lines maybe routed to a legacy charging hardware block (for examples, Battery Charging (BC) 1.2, Quick Charge (QC) 4.0)
Figure 5. Type-C Source with Plug
- Type-C only Sink with Plug:
Because this is a sink, Rd (5.1k) will be the termination which will be connected to the CC pin. This will act as an Upstream Facing Port (UFP – USB device) which will sink power. Only one of the SS lanes need to be routed to the SS physical layer.
Figure 6. Type-C Sink with Plug
- Type-C Only Source / Sink with Receptacle:
Here, the CC lines are monitored and terminated by a Type-C port controller such as Cypress CCGx. CCGx will present Rp termination in the case of source (host), and Rd termination in the case of sink (device) on both the CC lines. The USB High-Speed lines from top and bottom rows of the connector are shorted accordingly as shown in Figure 7. This short cannot be applied to SuperSpeed lines because it will create a stub at 5 Gbps data rates and cause signal deterioration. A SuperSpeed multiplexer will be used to switch between the two SS lanes of the Type-C connector, which will be controlled by a controller like CCGx or FX3. See KBA218460 for more details on SS mux control.
Figure 7. Type-C Only Source / Sink with Receptacle
Note:
- For replacing a USB 2.0 connector with a Type-C connector, just terminate the CC lines with the corresponding terminations Rp or Rd, and route the High-Speed lines as shown in figures 2-7. Other unused pins can be left open.
- A Type-C port controller (like CCGx) will be required when the application requires Power Delivery (PD), or/and there is a need to control the SS mux. If the Type-C controller is not used in a receptacle design, the receptacle will work only for one orientation. Termination of the CC lines for UFP / DFP also needs to be asserted as discrete components if the port controller does not have them integrated.
- The addition of a mux in the SuperSpeed path will cause attenuation of the signals. If the legacy system is already tight with signal integrity, the mux might cause failure of the SS connection. Therefore, in such cases, an active mux can be used which will perform redriving and retiming of the SS signals. The active mux will draw some power that needs to be considered in power budgeting.