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RPi 5 USB C PD

WA9ONY over 1 year ago

I there a way to check the RPi 5 to see what USB C PD and USB C Emarker cable configuration is being used?

I believe if the USB C cable does not have a Emarker, the USB C PD current level will be limited to max 3A and to max 20V.

Therefore, using a USB C cable with no Emarker will result in a USB C PD being limited to 3A even if it can supply 5A.

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0 wolfgangfriedrich over 1 year ago

One would need to record and decode the messages that are sent over the CC line. There must be a very non-standard profile being sent by the official RPi power supply. Alternatively they might be using vendor defined messages, which are part of the PD communication messages spec.

When I have my equipment back and get my hands on RPi5 equipment, I would love to go down that rabbit hole.
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0 shabaz over 1 year ago in reply to wolfgangfriedrich

Or they may have taken the lazy approach, and simply allow the power lines to draw 5A regardless of the limit that would be associated with the negotiation! : )

i.e. I'm wondering if their AC-DC converter simply is not monitored at 3A, since it's just a sense-resistor change to make their chip think it's within spec.
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0 shabaz over 1 year ago in reply to wolfgangfriedrich

Or they may have taken the lazy approach, and simply allow the power lines to draw 5A regardless of the limit that would be associated with the negotiation! : )

i.e. I'm wondering if their AC-DC converter simply is not monitored at 3A, since it's just a sense-resistor change to make their chip think it's within spec.
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0 wolfgangfriedrich over 1 year ago in reply to shabaz

Yeah, I am sure it does not limit the current. But still the RPi5 needs to know that it is connected to an official PS, to allow 1.6A for the USB ports as WA9ONY describes.

I had an early (before e-marker cables) 95W power supply, it was happily supplying 5A at any voltage. Was great for testing trigger boards.
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0 shabaz over 1 year ago in reply to wolfgangfriedrich

Ah, good point. I had forgotten about that.

I tore apart a Microsoft laptop power supply brick the other day, and they were monitoring current using an INA213 chip, which was neat. But that was a £100 power supply.
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