What is USB-C PD and can it be used in Ham Radio?

 As most of us are aware, USB is a data transfer protocol which has been revised from the original Universal Serial Bus to the latest USB4, with data transfer speeds up to 80 Gbit/s. Type C is the designation of the connector which you are familiar in mobile phone chargers. Type A plug and socket are the ones you connect with your laptop and type B the one for your printer. A cable to the printer from the laptop will have type A plug at one end and type B plug at the other end. My FT-710 radio uses a similar cable for CAT control or Computer Assisted Transceiver control as well. PD stands for power delivery and the current USB cables are capable of power delivery with rapid charging of devices including mobile phones with varying levels of voltage and current. Original USB devices could deliver only 5 V while the latest ones can deliver even up to 48 Volts and 240W. The white cable is a conventional USB type A to type C cable. The black one is thicker USB-C PD or power delivery cable.


USB type C connector has 24 pins and is reversible, meaning that it can be connected with any side up or down. Though the USB protocols for data transfer are different from the designation of the connectors, the latest USB4 protocol released in 2019 is implemented only through USB-C. Reverse symmetry is visible between upper series numbered with A and lower series numbered with B. There are four ground connections, two on either side. TX and RX stands for transmit and receive signals. They are meant for Enhanced SuperSpeed data transfer in USB 3 using shielded differential pairs. D stands for differential pairs taking legacy USB 2.0 high speed data transfer with unshielded twisted pair cables. SBU stands for sideband use and CC for configuration channel. VBUS is the bus power supply line.

This picture illustrates the typical unshielded twisted pair used in legacy USB cables for low, full and high speed data transfer (D± signals). Twisted pair is meant to reduce noise and crosstalk. As already mentioned, Enhanced SuperSpeed data transfer in USB 3 uses shielded differential pairs. USB C cable has only 16 wires though the connector has 24 pins. That is because B6 and B7 have no connections as seen in the plug pinout diagram and four ground and four VBUS pins are connected to the same solder joint. In USB-C PD standard, the source monitors the supply current to avoid overcharging. This is done by negotiation between source and sink. Properly designed circuits will also check short circuits between pins and will pay attention to electrostatic discharge surges. Latest type-C port protection associated with a microcontroller can even detect moisture in a USB port.

As mentioned initially, USB-C PD cable can deliver higher amounts of power. Raspberry Pi 5 supports the PD protocol. You may be aware that Raspberry Pi is being used in ham radios like Radioberry and sBitx, though currently they use Raspberry Pi 4 and Raspberry Pi 5 compatibility has not been mentioned. Using a USB-C PD protocol with Raspberry Pi 5 is a future expansion possibility. A PD charger needs to have a type-C port protection (TCPP) which starts with 5 V mode and then negotiate through configuration channel (CC) lines to define the optimum charge mode. If no negotiation is possible, the charger remains in 5 V. In that way over voltage is not delivered to an incompatible device. Legacy mode provides for up to 15 W power at 5 V and 3 A. SPR mode or Standard Power Range provides for up to 100 W with 20 V and 5 A, while Extended Power Range or EPR mode is capable of 240 W at 48 V and 5 A. Obviously these higher ranges needs compatible cable and charger and of course the device capable of receiving it.

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