In a notebook or PC implementation, a single USB-C port has the ability to sink USB PD voltages in order to charge the battery; provide at least 5V out to power small connected devices such as mice, keyboards and flash drives; and connect a monitor. You can quickly see how the required capabilities of a USB-C port is robust and flexible enough to meet the end user’s expectations for certain end equipment.

Figure 50 shows the power architecture for this type of system. There are typically separate power paths in the system: one for sourcing the 5V and another for sinking up to 20V. If you only have one USB-C port in the system, you could implement a single power path rather than two separate ones. In such cases, you would need the battery charger to have bidirectional support, and include on-the-go support. Most systems that require 5V source and 20V sink as well as DisplayPort Alternate Mode support will have more than one USB port.

If the end equipment will have multiple USB ports, a shared 5V rail can provide the sourcing power for both USB Type-A and USB-C ports. You will need to calculate the power budget of this 5V DC/DC supply based on the maximum current supported by each USB port when sourcing 5V to connected devices.

Connecting the sink power path to the battery charger isolates the capacitance from the battery charger from V_BUS, while also making sure that the battery charger receives power when the user connects an AC/DC adapter.

As in the previous examples, the USB PD controller will have integrated power path or provide a method to control them through GPIOs. Some USB PD controllers offer a N-channel field-effect transistor (NFET) gate driver to drive external NFETs directly.

Figure 50 also shows that the USB PD controller has the ability to supply V_CONN. The USB PD source-only design requires V_CONN when exceeding 3A of current. But adding support for DisplayPort Alternate Mode requires V_CONN in order to determine the data capabilities of the cable, not the power capabilities. Similar to the 5V USB-C source-only port with USB 3.0 data example, it’s important to confirm that the connected cable has capabilities for supporting DisplayPort Alternate Mode as well. V_CONN needs to power the e-marker in the cable in order to read back its capabilities.

Figure 51 shows a more complete block diagram that includes both the power and data blocks for implementing a 5V source, 20V sink USB-C port with USB PD and DisplayPort™ Alternate Mode design.

The last block in Figure 51 is the DisplayPort Alternate Mode multiplexer. As in previous cases, DisplayPort Alternate Mode also uses the SuperSpeed pins on the USB-C connector to transmit video data.

DisplayPort Alternate Mode includes several different pin configurations that help determine the distribution of the SuperSpeed pins between supporting USB 3.0 or DisplayPort video data. There are pin configurations that enable maximum bandwidth for DisplayPort by dedicating all SuperSpeed pairs for DisplayPort, and pin configurations that split the SuperSpeed pairs to enable both USB 3.0 and DisplayPort data simultaneously. The DisplayPort specification has further details about the pin configurations supported on USB-C.

The DisplayPort Alternate Mode multiplexer will multiplex the SuperSpeed pins to either the DisplayPort host or USB host, depending on the pin assignment negotiated within DisplayPort Alternate Mode. As with other peripheral devices, the USB PD controller is expected to communicate over I²C or with GPIOs to the DisplayPort Alternate Mode multiplexer to configure it accordingly. If the port partner also supports DisplayPort Alternate Mode, the USB PD controller will automatically negotiate and enter DisplayPort Alternate Mode with the connected device. Based on this negotiation, the USB PD controller will then configure the DisplayPort Alternate Mode multiplexer through either I²C or GPIO. During USB PD negotiation, power always gets negotiated first, followed by alternate modes such as DisplayPort.