I pulled up the actual USB power delivery standard[1] USB_PD_R3_1 V1.8 2023-04.pdf, and 5V 5A is perfectly compliant, albeit optional.
On page 805 you find Table 10-2 SPR Normative Voltages and Minimum Currents, which specifies that a USB PD source with a rating of 15 < x ≤ 27 watts *shall* support 3A at 5V, however it *May* advertise up to RoundUp (PDP/Voltage) to the nearest 10mA. Requires a 5A cable if over 3A is advertised. 27W/5 rounded to the nearest 10mA comes to 5.4A
The problem here is that a power supply offering 5V 5A is compliant, but a device requiring a 5V 5A source is not.
If a device needs 25W it is required to accept 9V 2.8A, if it wants to be PD compliant. This is precisely because 5V 5A is optional for a 25W source, so a device cannot rely on it being present.
It’s worth noting that this is _allowed_ by the USB-PD spec, but you’re right that 5V @ 5A is not common because it is not required. At least it’s better than the Pi 4 was at launch? :D
It doesn't need it, on the blog they say that if you use a standard 15W USB supply, it (by default) limits the board's USB output current so it can't cause a power failure at 100% CPU.
Oh, I see, so 100% CPU with no USB devices can run fine on 5V3A? That's nice to know. I could just use a powered hub for USB devices then.
I wish they had an auxilary DC power connector of some sort though that could just power the Pi on straight up + and - from a DC power supply. Ideally anywhere from 5-12V.
> When using a standard 5V, 3A (15W) USB-C power adapter with Raspberry Pi 5, by default we must limit downstream USB current to 600mA to ensure that we have sufficient margin to support these workloads. This is lower than the 1.2A limit on Raspberry Pi 4, though generally still sufficient to drive mice, keyboards, and other low‑power peripherals.
This is also very uncool, since powering it through the GPIO header with a capable PSU won't trigger the PD signal and makes it impossible to draw any meaningful current through USB? I hope this blockade can be worked around in the boot config.
I mean theoretically dupont connectors are rated for 2.5 A so two of them could get it done, but the current will never be completely equal across both and one may get overloaded. Maybe the safest option would be to find some kind of barrel-jack-to-usb-c dongle.
In practice I doubt it would be a real problem since you'd need to max out both the USB draw and CPU load at the exact same time to get the full draw.
None of your 100W Anker or Apple power bricks will supply this. They'll do 12V3A, 12V5A, 20V5A, but not 5V5A.
Yet another piece of nonstandard USB-C equipment.