Building CT-VPD dongle with ST products

[VasylV]

Hi all.

Are there any guides on building the charge-through VPD device with the ST product? An illustration from the standard:

The goal is to maintain the smartphone's supply from the external PD charger while maintaining the connection with a USB 2.0 auxiliary device (specifically, the simple USB CDC device). The auxiliary device consumes <0.1 W.

[FBL]

Hi @VasylV 

TCPP02 and TCPP03 can manage up to 0.1W using Vconn. From HW point of view, that should be ok.

However, there are no guidelines as done with SINK / SOURCE / DRP cases with examples. VPD is not supported on current library.

[VasylV]

Hi, and thank you for the comment!

I've looked through the ST portfolio, and if I stop focusing on VPD mode, STM32G071C8U6 might be a good match.

If I understand correctly, an ST MCU with two PD blocks can cover such an application. One port will act as a pure sink, and the other will be a DRD DRP port. The sink will authorize the highest advertised PDO, subtract its consumption + consumption of the auxiliary circuit, and re-advertise a smaller PDO to the dual-role port.

After studying the quick guide for dual role port, I'm sure your software could handle such an operation (role swap + FRS) with a bit of aux vdd capacitance to cover FRS transient. But I am unsure if the MCU can handle such an operation here. Your comment on that is highly appreciated.

Regards.

[FBL · Accepted solution]

Thank you @VasylV, STM32G071C8U6 is perfect for described. 

But you may face some limitations since swapping timings are too aggressive for FRS to manage voltage regulation. When Vbus drops below vSafe5V till the new source starts supplying USB Type-C current, this period/delay must be less than 150us. Check section 11.3.5 Dual-role power port with FRS in AN5225 for more details.