USB Type-C UFP sink: USB 2.0 without USB PD

The most simple and likely most common application is a UFP USB 2.0 without USB PD (≤15 W). Common applications include anything USB-powered today that does not require SuperSpeed data, such as a mouse, keyboard, wearables or various other small electronics. Figure 2 highlights the necessary functional blocks for a USB Type-C UFP USB 2.0 system.

At this point, we will assume that you understand the USB Type-C connector pinout and how reversibility works; if not, see Figure 13. Note that the USB 2.0 physical layer (PHY) is no different than previous USB 2.0 designs with a Type-A or Type-B connector. It serves as the physical layer between the data from USB’s D+ and D– lines to the USB 2.0 Transceiver Macrocell Interface (UTMI) plus low-pin interface (ULPI) for the application processor to manage.

USB 2.0 PHYs are often integrated into processors or microcontrollers; however, there are discrete PHYs available to integrate USB functionality into your design. The configuration channel (CC) logic block introduced in the USB Type-C specification determines cable detection, cable orientation and current-carrying capability.

• Cable detection occurs when one of the two CC lines pulls down (see Figure 3). A DFP will have both of its CC pins pull up with resistor Rp, and a UFP will have both of its CC pins pull down with resistor Rd [1]. Once a DFP processor detects that one of its CC lines is pulled down, the DFP will know that a connection has been made.
• Cable orientation is based on which CC line pulls down (if CC1 pulls down, the cable is not flipped; but if CC2 pulls down, the cable is flipped). For nonactive cables, the remaining CC line remains open; for active cables, the remaining CC line will pull down with Ra.
• The values of Rp determine the current-carrying capability. USB Type-C can natively support either 1.5 A or 3 A. A DFP can advertise its current-carrying capability with a specific value pullup resistor. A UFP has a fixed- value pulldown resistor (Rd) such that when connected, it forms a voltage divider with Rp. By sensing the voltage at the center tap of the voltage divider, a UFP can detect the DFP’s advertised current.

The last block is a USB 2.0 multiplexer (often called a high- speed mux). The dotted outline in Figure 2 represents an optional block not required by the USB Type-C specification. To understand the purpose of the mux, it’s important to understand how flipping the cable affects data flow. In a USB Type-C receptacle, there are two pairs of D+/D– lines for a single channel of USB 2.0 data. In one orientation, data flows down one of the pairs. In the flipped orientation, data flows down the other pair. The USB Type-C specification allows shorting the pairs together, D+ to D+ and D– to D–, to create a stub. Although it’s not required, some designers elect to include a USB 2.0 mux in their system to improve signal integrity.

Texas Instruments (TI) offers a variety of devices for UFP applications with USB 2.0 data and no USB PD. These devices from TI offer a compact solution for CC logic that can determine cable detection, orientation and current- carrying capability.