4 Implementing an isolated USB Type-C DRP

Figure 4-1 shows the block diagram of a self-powered isolated USB Type-C DRP.

The first and main requirement is to have an isolated USB repeater that does not have fixed upstream- and downstream-facing sides, but allows those roles to change dynamically. In such a repeater, 15-kΩ pulldown resistors are included on both side 1 and side 2, and enabled at power up. After that, whichever side detects a 1.5-kΩ pullup on DP or DM assumes the role of the upstream-facing port and disables its 15-kΩ pulldown. The other port assumes the role of downstream-facing port and keeps its 15-kΩ pulldown resistors enabled.

The second component in Figure 4-1 is a USB Type-C controller that can control the Rp and Rd resistors on the CC lines, interpret the state of the CC lines, and output information on the host or peripheral role, current being advertised by host, and so on. Next, an isolated DC/DC converter provides power to the USB Type-C controller and to the USB isolator’s secondary side. Lastly, a power switch on the VBUS turns on when the USB Type-C controller detects a peripheral connection; that is when the DRP has to assume a host or downstream-facing port role.

Most industrial applications are self-powered; in other words, they do not need to draw power from the VBUS when in peripheral mode. Therefore, Figure 4-1 and Figure 5-1 only show a unidirectional isolated power supply from the controller side to the connector side. Dual-role applications that need to draw power from the VBUS (for example, battery-powered applications) may require a bidirectional isolated DC/DC power supply, battery-charging circuitry and additional controls.