merriam
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RPI4 USB C Power Delivery negotiation

Mon Jun 24, 2019 2:48 pm

I have all sorts of USB power adapters to power/charge cell phones, lap tops and such. The device and the power supply negotiate voltage and amperage and settle on something they both can supply and use. Can I use those power adapters with RPI4? Will it negotiate what it wants? Or do I need to use the power supply developed by the foundation which provides the "right" power?

Bill

technix
Posts: 120
Joined: Sat Jul 13, 2013 4:55 pm

Re: RPI4 USB C Power Delivery negotiation

Mon Jun 24, 2019 3:34 pm

I am gonna second this on the question. If Pi 4 can negotiate properly over USB-C, it means for people that have difficulty buying official Raspberry Pi accessories, the power adapter and charging cable for Apple Retina MacBook or iPad Pro can be used as an alternative.

p.s. Suggestion: is it possible to implement 9V 3A over USB-C down the road? This allows the Pi to draw up to 27W from said Apple MacBook power adapter, allowing a total of 15W to go to the USB ports.

pcmanbob
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Re: RPI4 USB C Power Delivery negotiation

Mon Jun 24, 2019 6:33 pm

I don't think there is any negotiation but if you watch this review from 11:20 powering with a phone charger is mentioned, but its still only 5v at 3A phone charger.
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RattusRattus
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Re: RPI4 USB C Power Delivery negotiation

Mon Jun 24, 2019 6:43 pm

Hi there

Looking at the reduced schematics provided publicly for the RPi4 [1] we can see that there USB-C power pin (J1.VBUS) is directly connected to the primary 5V power rail.

This means that the Pi4 can ONLY accept 5V input from your power supply. There will be NO higher voltage negociation.

USB-C uses the Power Deliveray Specification to negociate for anything over 5V [2], but with connector pins J1.CC1 and J1.CC2 commoned togeatherthere can be no negociation taking place so the power supply is only allowed to give 5V (technically up to 2.1A max, 3A is supposed to be negociated for - but I don't see many people enforcing that limit)

USB-C has already been bastardised by some vendors - for example adding in Qualcomm's quickCharge 2 or 3 protocols. These not use the Power Delivery Specification, instead they use the D+/D- lines of the USB 2.0 port to negotiate the voltage [3]

So to sumerise:
NO. A USB C power supply will only provide a maximum of 2.1A @ 5V DC to a RPi4 whilst remaining fully compliant to USB-C specs. Some (most?) will let you have upto 3A @5V....

Regards
/RattusRattus


[1] https://www.raspberrypi.org/documentati ... educed.pdf
[2] http://www.ti.com/lit/an/slva842/slva842.pdf
[3] As the RPi 4 has populated USB2 on the J1 socket it is possible that malicious code running on your Pi *could* negociate for and receive a higher voltage whether or not this would be enough to take out the over voltage protection on a Pi remains to be seen...

dp11
Posts: 8
Joined: Thu Dec 29, 2011 5:46 pm

Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 9:09 am

A USB Type C power supply( or Source which could be a computer) has two possible ways to negotiate power. The simplest method is a resistor in the PSU to tell the device how much current it can supply at 5v, this is known as Rp.

Summary of table 4.24 from Universal Serial Bus Type-C Cable and Connector Specification

Code: Select all

Rp( to +5v in PSU)     Current available at +5v
56K                               Default USB power ( if the port is USB 2 then it is 500mA , if USB3.0 then 900mA )
22K                               1.5A
10K                               3.0A 
 
There is no reference to 2.1A in the specification.

The Raspberry Pi 4 official PSU has a 10K resistor in it to signal to the device it is capable of supplying 3A

jrodin
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Joined: Tue Jun 25, 2019 9:54 am

Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 9:57 am

So, bottom line, is it likely to work with, say, an Apple MacBook's 29W power supply?
Or a generic USB C 3.0A charger?

jamesh
Raspberry Pi Engineer & Forum Moderator
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Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 10:03 am

jrodin wrote:
Tue Jun 25, 2019 9:57 am
So, bottom line, is it likely to work with, say, an Apple MacBook's 29W power supply?
Or a generic USB C 3.0A charger?
My Pi4 is running off an Inateck device with no problems, and we did test a number of different supplies during development. So I see no reason why other devices would not work. Try it and see!
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dp11
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Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 10:09 am

Any 15Watt or greater TypeC charger that meets the USB specification should be fine. If your charger has a socket it is important that a good quality USB cable is used.

quavoce
Posts: 109
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Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 10:52 am

My RPi4 4GB arrived today (yay!!), but it seems I have nothing to power it with yet (boo) as the official PSU is due to arrive from another supplier later this week.

Based on comments in this thread, I tried to power the Pi using my MacBook Pro 87W USB-C Power Adapter with the Apple USB-C cable, but nothing happened on the Pi - no lights of any sort.

Should this PSU work? It's output rating does include 5.2V, 2.4A (along with 9V 3A and 20.2V 4.3A)

TIA

jamesh
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Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 11:14 am

quavoce wrote:
Tue Jun 25, 2019 10:52 am
My RPi4 4GB arrived today (yay!!), but it seems I have nothing to power it with yet (boo) as the official PSU is due to arrive from another supplier later this week.

Based on comments in this thread, I tried to power the Pi using my MacBook Pro 87W USB-C Power Adapter with the Apple USB-C cable, but nothing happened on the Pi - no lights of any sort.

Should this PSU work? It's output rating does include 5.2V, 2.4A (along with 9V 3A and 20.2V 4.3A)

TIA
Interesting - just tried a Dell USB-C power supply (actually from my docking station, which in turn is from a barrel connector) and that didn't work either. Obviously doing some sort of weird negotiation (AKA vendor lock-in).
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
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jrodin
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Joined: Tue Jun 25, 2019 9:54 am

Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 11:33 am

quavoce wrote:
Tue Jun 25, 2019 10:52 am
My RPi4 4GB arrived today (yay!!), but it seems I have nothing to power it with yet (boo) as the official PSU is due to arrive from another supplier later this week.

Based on comments in this thread, I tried to power the Pi using my MacBook Pro 87W USB-C Power Adapter with the Apple USB-C cable, but nothing happened on the Pi - no lights of any sort.

Should this PSU work? It's output rating does include 5.2V, 2.4A (along with 9V 3A and 20.2V 4.3A)

TIA
Maybe the issue is that it lacks the 15W (5V, 3A) profile? I just checked my Apple 29W and 61W USB C chargers and they also don't list the 15W profile.

Apparently the 18W Apple power supply does support the 15W profile. See:

https://www.chargerlab.com/apple-18w-us ... e-and-out/

I'm not sure if that's the issue, though. I don't expect to receive my PI4 until Sunday, so won't be able to try with the 29W and 61W Apple power supplies until then.

In the meantime, anyone else who can shed further light on the matter would be doing a great service to the community.

jrodin
Posts: 5
Joined: Tue Jun 25, 2019 9:54 am

Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 11:40 am

There's also a relevant discussion near the end of this article comparing the various Apple USB C chargers and their levels of standard's compliance:

https://switchchargers.com/apple-61w-review/

quavoce
Posts: 109
Joined: Fri Nov 27, 2015 9:11 am

Re: RPI4 USB C Power Delivery negotiation

Tue Jun 25, 2019 1:06 pm

Thanks, must be a vendor lock in as suggested.

I have an Anker 15W adapter arriving tomorrow so will report back if that works.

Anker USB C Wall Charger, 15W 5V/3A PowerPort C 1 Type C Charger, Super Compact with LED Indicator, for iPhone XS/Max/XR/8, Pixel 3/2/XL, iPad Pro, Galaxy S9/S8/Plus, and More https://www.amazon.co.uk/dp/B07HFNC9Z3/

jrodin
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Re: RPI4 USB C Power Delivery negotiation

Thu Jun 27, 2019 7:46 pm

Quick update. I tried both the 29W and 61W Apple USB C power adapters and they didn’t work. Until I get hold of a suitable USB C charger, I’m using the Pi3 charger with a micro-usb to type C adapter. So far it seems fine.

scorpia
Posts: 18
Joined: Mon Oct 08, 2018 10:54 am

Re: RPI4 USB C Power Delivery negotiation

Fri Jun 28, 2019 12:18 am

I would expect that any vendor restrictions on Type-C charger capabilities would be at the power delivery stage (which the Pi doesn't look to do) as there isn't much scope for communication between charger and device before that. I suspect the issue is a result of the pi only having a single cc pulldown resistor (there should be two) on the USB connector on the pi. I have stared a discussion on this here https://www.raspberrypi.org/forums/view ... 3&t=243875 were there is also a technical write-up for those interested in the specifics.

jarrah31
Posts: 125
Joined: Wed Oct 10, 2012 10:16 am

Re: RPI4 USB C Power Delivery negotiation

Fri Jun 28, 2019 7:01 am

Interesting article @scorpia!

I too have a MacBook Pro 87W adapter and Apple USB-C cable that didn't work on my Pi4, but I tried another USB-C cable I had lying around and it worked with the Apple adapter! So, the Apple adapters are fine, it was just the cable!

KARLSON
Posts: 1
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Re: RPI4 USB C Power Delivery negotiation

Fri Jun 28, 2019 4:03 pm

My Samsung Galaxy S8 charger runs well in RPI4, 3 days of continous use.

jay_rious
Posts: 1
Joined: Sun Jun 30, 2019 4:54 pm

Re: RPI4 USB C Power Delivery negotiation

Sun Jun 30, 2019 5:00 pm

jrodin wrote:
Tue Jun 25, 2019 11:33 am
quavoce wrote:
Tue Jun 25, 2019 10:52 am
My RPi4 4GB arrived today (yay!!), but it seems I have nothing to power it with yet (boo) as the official PSU is due to arrive from another supplier later this week.

Based on comments in this thread, I tried to power the Pi using my MacBook Pro 87W USB-C Power Adapter with the Apple USB-C cable, but nothing happened on the Pi - no lights of any sort.

Should this PSU work? It's output rating does include 5.2V, 2.4A (along with 9V 3A and 20.2V 4.3A)

TIA
Maybe the issue is that it lacks the 15W (5V, 3A) profile? I just checked my Apple 29W and 61W USB C chargers and they also don't list the 15W profile.

Apparently the 18W Apple power supply does support the 15W profile. See:

https://www.chargerlab.com/apple-18w-us ... e-and-out/

I'm not sure if that's the issue, though. I don't expect to receive my PI4 until Sunday, so won't be able to try with the 29W and 61W Apple power supplies until then.

In the meantime, anyone else who can shed further light on the matter would be doing a great service to the community.
Interestingly, I tried my MacBook Pro 61W USB-C power supply on my PI4 yesterday and it WORKED! I installed the Raspbian system and everything went fine. I shutdown the system and unplugged the power supply......and it won't boot today..... no LED blinking, nothing happens when I plug the power supply. I reformatted the micro SD card and copied NOOBS files but still nothing happens...

I'm wondering if the 61W USB-C power supply was harming my PI4? Should I buy a 15W power supply instead?

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