NUCLEO-U575ZI-Q USB-C CC1/CC2 capacitor placement

[ChristianB]

We designed a custom made board based on NUCLEO-U575ZI-Q schematic. Specifically, we copied the USB-C connection part including the TCPP01-M12. The design is BUS powered. The devices are only recognized if connected via USB-A to USB-C adapters or if the CC1/CC2 pins are shortly shorted to GND while plugged in an USB-C connector, i.e. forcing an re enumeration.  In the Nucleo schematic capactors (C62 & C 63)are placed at CC1/CC2 between MCU and the TCPP01-M12:

The TCPP01-M12 datasheets places them on the CC1c/CC2c pin, i.e. between USB connector and the TCPP01-M12:

Furthermore it specifies:

After rewiring the caps the boards are recognized more reliable but still some fail. So questions are:

-is the TCPP01-M12 functionallity influenced by the placement of the capacitors at CCxc vs CCx?

-what are potential reasons to fail negotiations while plugging in (i.e. only voltages at CCxc pins and VBUS is low - disconnected by host) but succeeding if CCxc is shorted shortly?

P.S.: we are still investigating the influence wether the DB/ connected to the MCU might have an influence.

[ChristianB · Accepted solution]

The solution is humbling:

The working devices had a short in the rewiring forcing one CC line to GND. Reason why this resulted in working devices is that the intended use is to directly plug them into an USB port. So no cable inbetween. This means both CC lines are directly connected. Appearently the orientation detection relies on only one CC makes connection. Thus pulling the other line to GND solved the issue.

[FBL]

Hi @ChristianB 

USB PD negotiation relies on the CC lines to detect power roles, current capabilities, and cable orientation. USB-A ports and connectors do not have the CC (Configuration Channel) pins required for USB PD communication.