I’d like to use STUSB4500 to allow for 20V 60+W to enter the system, but I’d also like to use the sideband pins (or other pins) to send some serial data to the host side. I’d like to know whether this is possible (seems like the chip doesn’t use SBU pins to deliver power), and whether this use of SBU during PD is compliant with USB specs.
The SBU pins are not connected to the Sparkfun STUSB4500 board, they are not used at all. For the PD setting, it is using the CC1 and CC2 pins so use the SBU pins as you like. Last year I studied the board and chip in detail and wrote an extension/analyzer for the Saleae Logic 8. You can find that and the learning on https://github.com/paulvha/HLA_I2C_STUSB4500.
Thank you for the reply Paul!
In the USB-C specs, 4.3: "The SBU pins on a port shall either be open circuit or have a weak pull-down to ground no
stronger than zSBUTermination when in USB 3.2 or USB 2.0." Do you think USB PD is part of these two specs or is it a separate spec, ie. I don’t have to leave SBU with pd or oc?
The SBU pins are NOT used at all by the STUSB4500. All the STUSB4500 does is handle PD and provide the requested voltage and current based on the source capability. The onboard QWIIC connector is only used to access and configure the STUSB4500 registers. Nothing more nothing less. Somehow you need to make a junction between a cable from the STUSB4500 that delivers the power, to a cable that connects 2 USB devices where you want to communicate with each other using SBU.