SLYY228 November 2024
A 20V USB-C sink-only port with USB PD is relatively easier to design than a source port. According to the USB PD specification, the source port is required to manage most of the power protections and control the voltage across the cable. The sink side mainly requests the connected source for voltage or current in the form of a PDO and completes USB PD negotiation.
In this implementation, the system likely receives its power from the USB-C port. With the expansion of USB-C and some countries now mandating adoption of the USB-C connector, devices that have historically been powered by a barrel jack, coaxial cable or other proprietary DC input must now have charge via a USB-C port. A few end-equipment examples would be Wi-Fi® adapters, Bluetooth® speakers, and e-bikes and e-scooters.
Similar to the 5V USB-C sink-only port, a USB PD sink-only port could also be required to implement a power path. The decision to add a power path will depend on the amount of capacitance exposed on VBUS. From the USB-IF specification, you’re only allowed 10µF of capacitance on VBUS, so if your system requires more, you’ll need to add a power path to isolate the system capacitance from VBUS.
Figure 12 is a basic system-level block diagram for implementing a 20V USB-C sink-only port with USB PD design. The main difference between a USB-C 5V sink-only design and a 20V USB-C sink-only port with USB PD design is that the load switch scales up to 20V, and you will need a USB PD controller instead of a CC controller.
Figure 49 20V USB PD sink only block
diagramAgain, support for USB 3.0 data necessitates the addition of a multiplexer.