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by rickdeckard 392 days ago
For 5V output (like used on the Pinebook) you don't need to negotiate anything over USB-PD, that's the default provided by a USB-C PSU to ensure legacy USB compatibility. Support for higher currents can then be "unlocked" with resistors between the Alt Data-Lines (like a USB-A charger would).

Everything beyond 5V requires a handshake between device and PSU, which ensures that the connected device can actual handle higher power output.
1 comments
nfriedly 391 days ago
It's arguably not "negotiation", but if the connector is USB-C on both ends, then even 5V requires a couple of resistors to determine which side is the source and which side is the sink.

It's pretty common for really cheap electronics to skip these resistors, and then they can only be powered with a USB-A to USB-C cable, not C-to-C. (Because USB-A ports always a source and never a sink.) Adafruit even makes a $4.50 adapter to fix the issue.

But you're right that everything higher than 5V & 3A gets significantly more complex.

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rickdeckard 390 days ago
All correct and agreed.

My comment was in context of the active communication between source/sink on USB-PD and the increased complexity, intentionally excluding passive configuration using different resistors.

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