I was looking at the USB-C PD board in the store, the USB-C PD DEEP DIVE on Gman's blog, and the datasheet for the stusb4500 chip, in order to learn more about how power delivery negotiation and other related concepts work. In doing so, I have been able to figure out the purpose of a lot of the ICs on the board, but there's one that I can't figure out. What is the U4 chip, and what does it do? I can't see any symbols or numbers to identify it. Can anybody help me out?