Questions about the USB power delivery


On Xavier’s official carrier board, two type-c ports share one DC-DC convertor. I wonder what would happend if two devices inserted with different power demands (e.g., different voltage) and also different sequence (e.g.,a 20V device is inserted first and the DC-DC output 20V, and a 5V device is inserted later; a 5V device is inserted first and a 20V device is inserted later). Are two DC-DC convertors needed for these sisuations or one is enough?


If you mean devices drawing power from the USB-C, then only 5V is supported in the USB standards. All devices drawing power from this should require a 5V supply. Any supply within the carrier board should be able to provide 5V output to the connectors at the sum of the two connector’s required minimum current limits.

Hi, linuxdev

There are USB PD(Power Delivery) components (CYPD4226, NCP81239MNTXG) on official carrier board and it should support USB PD with higher voltage such as 12V, 20V (not tested as I don’t have such USB PD test device).

We are designing a carrier board for Xavier module and wondering how to implement the USB PD part. The CYPD4226’s firmware is not opensource and the hardware design is a little confusing, so we want to know its behavior in above conditions.

I cannot answer that, I’m only familiar with the 5V delivery.

the PD (CYPD4226) will detect to use the firstly insert power such if you insert USB TYPE C power at firstly , then insert DC-DC power , the system will use the USB TYPE C power.

It sounds like what @rita_wangning is saying is that the Xavier dev board uses the power delivery circuits for RECEIVING power delivery, not for SOURCING power delivery.
Meanwhile, @linuxdev is talking about SOURCING 5V from the Xavier, which, AFAIK, only works at 5V.

Thank you guys. Now I have a USB PD monitor. Xaiver’s USB type c can provide 5V only (at least for now, the hardware supports different voltage, maybe it would provide different voltage with new firmware or driver), and it can sink 20V with a USB PD power source (not sure whether Xavier works if only 5V provided, as the max power seems not enough).

What will happen in the defined scenario if USB-c will be detached? will the board remain powered by DC-DC or will shutdown? In the latter case - is there any chance to prevent it from shutting down?

I can’t answer that, but even if both power delivery routes are valid, then there could be an issue with a power surge at the moment of disconnect. I don’t know if switching supplies would produce the problematic power fluctuation. I think you’d have to try it to know, and it could be dependent upon the particular power supplies and the current computing load.