Getting started with the STUSB4500QTR

[DavePfz]

I'm trying to get started with the STUSB4500QTR and at this point have not changed anything in the device but at the same time I am not using any of its capabilities. The attached schematic shows where I am now. The intent is that a PC (right now just Windows 10) would connect into the 'C' connector and a pigtail connector would carry the D+/D- lines on the the 'C' connector on a Raspberry Pi 4B+. That's what I'm trying to get going now. Eventually, my board (the schematic) would extract power, but that is not my immediate concern.

Right now, if I plug the 'C' cable from the PC directly into the Pi, it works is gadget serial mode - what I want. However, when I plug the PC into my board and the pigtail into the Pi, Windows does not recognize the device.

The pigtail is cut from an 'A' to 'C' adapter cable. The green/white wires are soldered into the test points. The Black and shield are wired in to ground on the PCB. (Red wire is left floating.) All wires are kept as short as possible.

What am I doing wrong? Must there be some setup of the STUSB4500QTR even though the power path is not being used?

Thanks for any pointers.

[RhSilicon]

I found this, see if it helps:

For simple USB-C usecases, like “get USB 2.0 and 5 V out of a port, follow a simple recipe – attach a 5.1 kΩ pulldown to each CC pin, and you will have a USB-C port that will work with all reasonable devices out there.

https://hackaday.com/2022/12/06/usb-c-introduction-for-hackers/

[DavePfz]

Thanks for the pointer. I had been following the USB-C series but missed that detail.

In looking at the Pi schematics, both CC1 and CC2 are pulled to ground through a 5.1K resistor. So, the Pi should be happy. On the PC (0r upstream) side, looking at the product sold by PiMoroni (https://shop.pimoroni.com/products/usb-c-pwr-splitter?variant=39299226992723 ), it looks like the side facing the PC needs to have both of these pulled up through 10K resistors. Does this mean that I should set up the STUSB4500 in some manner?

[RhSilicon]

USB is standardized by USB-IF, it may be interesting to search the documents to verify the information:

https://www.usb.org/documents

[DavePfz · Accepted solution]

The ESD protection diode D4 apparently was loading down the bus too much. Once removed the data path started working.

Now, I'm clear to start working on the power portion of the design.

Thanks for listening.