Oh god I just read about the RPi 5 power supply situation. It's so dumb.
From https://www.raspberrypi.com/news/the-inside-story-on-the-new-raspberry-pi-5-hackspace-72/ : RPi 5 needs > 15W in some situations, but they didn't want to put DC-DC converters on the board to use 9V/12V USB-PD modes.
So instead it looks like they have a hacky non-standard 5V/5A mode which only works with their own power supply?!
What the fuck.
@delroth And seems to be not just non-standard as uncommon, but actually not following the USB-C and Power Delivery standards (assuming my quick skim is correct)... and considering you need better cables for normal 5A USB-PD this is going to be "fun"...
@simonlbn @delroth The USB-PD spec supports a maximum of 5A at all voltages, but most implementations top out at 3A at 5V because apparently nobody is going to want 5V at 5A, right?
Pretty sure they’re not violating the spec - it’s more that a lot of chargers violate the spec by making assumptions. Given the ferocious heat budgeting that must go on in RPi design and the fact that buck/boost converters will always generate heat (and the higher the current, the more heat) I can understand not wanting to do that on the board.
@m @delroth
I got curious enough to download the spec rather than just reading secondary sources like I did before my first psot :-).
I think* you are correct. 5A @ 5V is allowed, but it's not required to be supported to be spec compliant.
* As in, it's a long spec, there could be other parts I missed :-).
This is from USB Power Delivery Specification Revision 3.1, Version 1.8 Page 805.
@simonlbn @m @delroth Page 815, section 10.3 Sink Power Rules
> A Sink optimized for a Source with Optional Voltages and currents or power as described in Section 10.2.3 with a PDP Rating of x W Shall provide a similar user experience when powered from a Source with a PDP Rating of ≥ x W that supplies only the Normative Voltages and currents as specified in Section 10.2.2.
It would be complaint if RPi5 also worked at full capacity with normative 27W sources over 9V or higher.
