There is no standard reference design. But few modifications in existing designs will work.
Can you provide some detail into the application?
Is it going to be a fixed UFP-power? And are there any specific reasons behind choosing CCG3PA?
CCG2, CCG3 and CCG3PA can do the job. With CCG3 and CCG3PA you will have the luxury of internal VBUS to VDDD LDO.
But you will not require the Battery charging, internal billboard and alt mode support provided by CCG3, so CCG3PA will be the best option for you.
With CCG3PA to sink power refer to the power bank reference design. The only change is to remove the FB - CATH/COMP feedback to the power converter, use only VBUS_C_CTRL, connect VBUS_IN_DISCHARGE to TYPE_C_VBUS instead of output of power converter (similar to powerbank reference design). In the configuration utility you can disable source PDO's and change default port role to sink. Add required Sink PDO's and it should be ready.
You can take help from Rad, I think he has a good design there which seems to be working well.