3 ms·

Does it not accept standard USB-PD?

by Hamuko 3y ago

ssl-3 3y ago
It does support USB-PD. It just doesn't do it in a way that many USB-PD power supplies work with. Whereas lots of USB-PD devices (at each end) will negotiate higher voltages in order to accomplish greater power delivery, the Pi 5 only ever wants 5V -- not 9V, not 12V, 15V, not 20V, and not PPS. Ideally, it wants up to 5A of 5V.[1] And many (I dare say "most," or "nearly all") USB-PD power supplies top out at 3A when in 5V mode. Also: Getting 5A of USB-PD also requires a special e-marked cable because that's getting into the realm of current flow where things can get melty. A dumb cable will never be expected to transmit 5A of current with a USB-PD device at each end. --- The Pi 5 still can still work even if it can't detect that it is running from a 5 Amp-capable supply, though. It may be slower (due to detected voltage sags), and there will be less power available for USB devices attached to the Pi (which can be toggled in config.txt). But it can work. It can also be powered through the GPIO header, just as other models in the past: Nothing prevents those who think they know what they're doing from using whatever they have laying around that they think is adequate, and just powering the device up in full capacity.[2] [1] https://www.raspberrypi.com/documentation/computers/raspberry-pi-5.html#powering-raspberry-pi-5 https://www.raspberrypi.com/documentation/computers/raspberr... [2] https://forums.raspberrypi.com/viewtopic.php?t=358008 https://forums.raspberrypi.com/viewtopic.php?t=358008
- sschueller 3y ago
  Isn't more than 3A at 5V out of USB-PD 2 and 3 spec? You can set max 3A amp for USB PD with just placing a 5.1k resistor on each USB CC line without the need for a USB PD IC. If you need more you would need to request for example 20V at 5A and then buck convert it down to 5V. Not ideal but you can at least pull the current you need through thinner cables and you also have enough to power external USB devices.
  - Kirby64 3y ago
    The “normal” way to support 25W would be to support 9V 3A input, giving 27W adapters functionality. Or possibly accept multiple options such as 9, 12, and 15, and then buck any of those down to the system voltage needed. The 5V5A is because raspberry pi org is being cheap/lazy and doesn’t want to design or pay for a power converter to handle that on the pi, and instead is pushing that complexity/cost to the user via an overpriced and nonstandard supply.
- cge 3y ago
  >And many (I dare say "most," or "nearly all") USB-PD power supplies top out at 3A when in 5V mode. 5 A at 5 V seems to be sufficiently unusual for USB-PD that Wikipedia's section on the specification doesn't mention it as being part of the specification at all, giving 3 A as the maximum in the specification for 5 V, and only mentioning 5 A with EPR and marked cables at higher voltages [1]. Discussions about 5 A at 5 V seem to come up essentially only in the context of the rpi5, and there most references seem to be to footnotes in the specification mentioning that more than 3 A can be advertised if a 5 A cable is detected. The rpi5 also apparently doesn't support 5 A at 5 V with PPS; it only supports it as a fixed voltage profile. The result would seem to be that essentially no USB-PD power supply other than theirs, and one other SBC power supply, actually offers 5 A at 5 V in a way that the rpi5 will accept. [1]: https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Deliver...
  - ssl-3 3y ago
    It is unusual. I'd even go as far as to say that it is an awful and stupid decision to do this at a time when USB-PD operating at higher voltages is finally becoming somewhat commonplace (common, as in: we might have extra junk laying around that can do it), but I'm not trying to make 90,000 widgets per month and build them down to a price. But a casual Google search where I am located at least two alternative suppliers that are already shipping appropriate power supplies that can do 5@5. And the usual (US) distributors (places like Adafruit and also places like Digikey) are selling the official power supply for $12, which I personally consider to be very cheap. --- And remember, wanting peculiar power supplies is normal in the RPi space. The very popular Pi 3 was weird (5.1V@2.5A over MicroUSB, with many unofficial recommendations suggesting 3A), for instance -- in a world where common "high-power" USB power bricks topped out at 5.0V@2.4A on a good day, with the wind from the South, and under the direction of an unladen sparrow. Many of us are familiar with the struggles that this entailed as we worked on whatever we were working on. But other suppliers did come to the front and offer alternative products that reliably delivered 5.1V@3A, and there's no indication that this won't be the case for this round as well -- especially if they're able to produce the quantity of RPi5s that they say they will. At a projected 90k units per month, then: Every 7 seconds, an opportunity to sell another RPi5 power supply opens up. (The Pi 4 has a different version of the same story.)
- gambiting 3y ago
  >>A dumb cable will never be expected to transmit 5A of current with a USB-PD device at each end. I mean, a lot of cables(Certainly all Anker ones) support 100W charging and that's 20V@5amps, so the 5amp part really shouldn't be a big problem.
  - izacus 3y ago
    Supporting 20V@5A doesn't mean they'll successfully negotiate for 5V@5A. That's the whole point of the post you're replying to.
  - mardifoufs 3y ago
    The issue isn't the cables. It's the USB pd wall adapters, that usually use the same broad range of USBPD ICs and those rarely support 5v5a. So you are fundamentally limited to almost just some raspberry centric hardware since no one else uses that USB PD level.
  - wkat4242 3y ago
    With 5V @ 5A the heat isn't the only problem, you also have a relatively higher voltage drop to contend with. Which the raspberry is also known to be pretty sensitive to. I imagine that will need even thicker cables to work reliably than 20V@5A.

Does it not accept standard USB-PD?

by Hamuko 3y ago

Does it not accept standard USB-PD?

It does support USB-PD. It just doesn't do it in a way that many USB-PD power supplies work with. Whereas lots of USB-PD devices (at each end) will negotiate higher voltages in order to accomplish greater power delivery, the Pi 5 only ever wants 5V -- not 9V, not 12V, 15V, not 20V, and not PPS. Ideally, it wants up to 5A of 5V.[1] And many (I dare say "most," or "nearly all") USB-PD power supplies top out at 3A when in 5V mode. Also: Getting 5A of USB-PD also requires a special e-marked cable because that's getting into the realm of current flow where things can get melty. A dumb cable will never be expected to transmit 5A of current with a USB-PD device at each end. --- The Pi 5 still can still work even if it can't detect that it is running from a 5 Amp-capable supply, though. It may be slower (due to detected voltage sags), and there will be less power available for USB devices attached to the Pi (which can be toggled in config.txt). But it can work. It can also be powered through the GPIO header, just as other models in the past: Nothing prevents those who think they know what they're doing from using whatever they have laying around that they think is adequate, and just powering the device up in full capacity.[2] [1] https://www.raspberrypi.com/documentation/computers/raspberry-pi-5.html#powering-raspberry-pi-5 https://www.raspberrypi.com/documentation/computers/raspberr... [2] https://forums.raspberrypi.com/viewtopic.php?t=358008 https://forums.raspberrypi.com/viewtopic.php?t=358008

sschueller 3y ago
Isn't more than 3A at 5V out of USB-PD 2 and 3 spec? You can set max 3A amp for USB PD with just placing a 5.1k resistor on each USB CC line without the need for a USB PD IC. If you need more you would need to request for example 20V at 5A and then buck convert it down to 5V. Not ideal but you can at least pull the current you need through thinner cables and you also have enough to power external USB devices.
- Kirby64 3y ago
  The “normal” way to support 25W would be to support 9V 3A input, giving 27W adapters functionality. Or possibly accept multiple options such as 9, 12, and 15, and then buck any of those down to the system voltage needed. The 5V5A is because raspberry pi org is being cheap/lazy and doesn’t want to design or pay for a power converter to handle that on the pi, and instead is pushing that complexity/cost to the user via an overpriced and nonstandard supply.
cge 3y ago
>And many (I dare say "most," or "nearly all") USB-PD power supplies top out at 3A when in 5V mode. 5 A at 5 V seems to be sufficiently unusual for USB-PD that Wikipedia's section on the specification doesn't mention it as being part of the specification at all, giving 3 A as the maximum in the specification for 5 V, and only mentioning 5 A with EPR and marked cables at higher voltages [1]. Discussions about 5 A at 5 V seem to come up essentially only in the context of the rpi5, and there most references seem to be to footnotes in the specification mentioning that more than 3 A can be advertised if a 5 A cable is detected. The rpi5 also apparently doesn't support 5 A at 5 V with PPS; it only supports it as a fixed voltage profile. The result would seem to be that essentially no USB-PD power supply other than theirs, and one other SBC power supply, actually offers 5 A at 5 V in a way that the rpi5 will accept. [1]: https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Deliver...
- ssl-3 3y ago
  It is unusual. I'd even go as far as to say that it is an awful and stupid decision to do this at a time when USB-PD operating at higher voltages is finally becoming somewhat commonplace (common, as in: we might have extra junk laying around that can do it), but I'm not trying to make 90,000 widgets per month and build them down to a price. But a casual Google search where I am located at least two alternative suppliers that are already shipping appropriate power supplies that can do 5@5. And the usual (US) distributors (places like Adafruit and also places like Digikey) are selling the official power supply for $12, which I personally consider to be very cheap. --- And remember, wanting peculiar power supplies is normal in the RPi space. The very popular Pi 3 was weird (5.1V@2.5A over MicroUSB, with many unofficial recommendations suggesting 3A), for instance -- in a world where common "high-power" USB power bricks topped out at 5.0V@2.4A on a good day, with the wind from the South, and under the direction of an unladen sparrow. Many of us are familiar with the struggles that this entailed as we worked on whatever we were working on. But other suppliers did come to the front and offer alternative products that reliably delivered 5.1V@3A, and there's no indication that this won't be the case for this round as well -- especially if they're able to produce the quantity of RPi5s that they say they will. At a projected 90k units per month, then: Every 7 seconds, an opportunity to sell another RPi5 power supply opens up. (The Pi 4 has a different version of the same story.)
gambiting 3y ago
>>A dumb cable will never be expected to transmit 5A of current with a USB-PD device at each end. I mean, a lot of cables(Certainly all Anker ones) support 100W charging and that's 20V@5amps, so the 5amp part really shouldn't be a big problem.
- izacus 3y ago
  Supporting 20V@5A doesn't mean they'll successfully negotiate for 5V@5A. That's the whole point of the post you're replying to.
- mardifoufs 3y ago
  The issue isn't the cables. It's the USB pd wall adapters, that usually use the same broad range of USBPD ICs and those rarely support 5v5a. So you are fundamentally limited to almost just some raspberry centric hardware since no one else uses that USB PD level.
- wkat4242 3y ago
  With 5V @ 5A the heat isn't the only problem, you also have a relatively higher voltage drop to contend with. Which the raspberry is also known to be pretty sensitive to. I imagine that will need even thicker cables to work reliably than 20V@5A.