PORTS Forum

Ports and Interfaces => USB => Topic started by: jb on October 27, 2020, 07:33:31 pm

Title: Various questions about Type-C Current
Post by: jb on October 27, 2020, 07:33:31 pm

• If a Device/Sink sees a 1.5 A or 3.0 A resistor on CC, then it must be connected to a Host/Source with a Type-C receptacle, right, since there's no way for an A port to advertise 1.5 A or 3.0 A on the CC pins?
• If a Device/Sink sees a 1.5 A or 3.0 A resistor on CC, then it can start drawing that much current immediately, with or without enumerating?
• If a Device/Sink sees a "Default" resistor on CC, then it must be connected to a legacy A-to-C cable? Type-C receptacles won't have "Default" resistors?  No, a Google Pixel has a C receptacle and "Default" resistors.
• If a Device/Sink sees a "Default" resistor on CC, can it draw 500 mA immediately, or does it need to enumerate first like a legacy USB 2.0 device?
• The spec says a "USB Type-C Power Sinking Device (PSD)" can "draw up to 500 mA" after connecting, but it has no USB communication ability, so wouldn't that imply that we can always draw 500 mA without enumerating?
• "A PSD shall fully support USB Type-C Current operation" so it could also draw 1.5 or 3.0 A immediately if it sees the right resistors?  The spec doesn't actually say this.

Title: Re: Various questions about Type-C Current
Post by: Jan Axelson on October 31, 2020, 11:39:40 am

These are good questions. I see you found the answer to one of them. I'm sorry I can't help with the rest. The USB specs can sometimes be challenging to figure out due to incompleteness or imprecise language.

Title: Re: Various questions about Type-C Current
Post by: jb on December 17, 2020, 10:59:48 am

Also, if a computer port uses CC pin to advertise >1.5 A, do you still have to drop to 2.5 mA in suspend?  Or can you draw 1.5 A in suspend?

I think I found the answer:

Universal Serial Bus Type-C (USB Type-C)Functional Test Specification Chapters 4 and 5 (https://usb.org/sites/default/files/USB%20Type%20C%20Functional%20Test%20Specification%202019%2004%2030.pdf) says

Quote

USB suspend power rules shall apply when the USB Type-C Current is at the Default USB Power level or when USB PD is being used and the Suspend bit is set appropriately.

1.5 A and 3.0 A are not Default level.

Quote

6. CVS transitions to Unattached.SRC advertising vRd-1.5 with Rp
...
8. If the PUT is USB 2.0 Capable:
a. CVS brings PUT to the HS/FS/LS Default state.
b. CVS suspends PUT.
c. Wait 1 second
d. CVS verifies the PUT draws suspend current up to 1.5 amps.

So it's ok to draw 1.5 or 3.0 A even during suspend.

Title: Re: Various questions about Type-C Current
Post by: Jan Axelson on December 17, 2020, 08:43:48 pm

Thanks for posting this.