USB to ethernet adapter with charging

[Teun]

Hi All,

I'm in dire need of some USB experts. What I would like to accomplish is a USB to Ethernet adapter with charging capabilities. Now I have looked around some and found this thing that can do exactly that.


It gives me ethernet function on the smartphone and charges it at the same time. Only 5W charging, but that would be enough.
This was the only adapter I could find that charged the phone in a relative fast way. I have some others but they only charge at about 0.5W of which most is probably used by the chips on the adapter. Or they cut the power to the phone as soon as the ethernet cable was connected and more funny stuff  like that.
What I got from the good adapter is that the power is somehow switched on to the UFP. If I understood the USB-IF documents right that is done trough a Charging Downstream Port. Now I have found some chips like the TPS2583xA-Q1 that I think could do that. So first question: Am I right?

Secondly, we have a solution at work where there is already a 5 way ethernet switch connected to some RTL8153 chips to have ethernet function on 5 phones in a docking station. These have been used with pogo pins on the bottom of the devices so we can also charge them at the same time. But now we need a similar product with USB-C connectors in stead of the pogo pins. So my next question: are there chips that sort of give me the CDP alone? Because we would like to use the existing products to achieve all this. And what would chips like that be named? I'm a bit lost in the jungle of USB-BC1.2 etc at the moment.

To clarify here is a block schematic of what we need. We would like something that can be put between the smartphones and the RTL8153 if that is possible.

[NiHaoMike]

Have you considered using a Raspberry Pi or similar and the free app "gnirehtet"?
https://github.com/Genymobile/gnirehtet

[Teun]

I don't really know much about raspberry pi's. How would that help me create this as an end product?

[mikeselectricstuff]

I think you may have issues due to the fact that the phone will have USB OTG, which is either a host of device - an ethernet interface is a 'device', which the host expects to supply power to.
Not sure if the OTG spec or any USB-C updates have changed this.
Is there a reason you can't use wifi instead of hardwired ethernet? 

[Jeroen3]

USB OTG is more complicated. I just bought a USB OTG hub for an rpi with a power input. So it must be possible.
Analog Devices even made a chip for it LTC3576. But it's from 2009, a relic in phone world.
USB Type C even throws USB-PD in the mix...

I'm sure it's posible. Cars do it, maybe lookup reference implementations of Android Auto and Carplay?

[ajb]

It's definitely possible to charge while connected to a downstream device, there are tons of docking stations for laptops that use one USB C connector to provide charging (at up to 100W even) as well as ethernet, display, and downstream facing USB ports.  The problem might be due to the way that USB functionality is implemented on the smartphone.  You might try plugging that adapter you have into a laptop with USB C and see if it will charge at a higher rate, that would tell you if it's an issue with the specific adapter you have or with the smartphone (or the combination of the two).  Another consideration: does the phone offer an option to change its USB behavior when you plug in the adapter? When I plug it into a USB device other than a charger, my (android) phone gives me the option to select whether I want the phone to charge from the device, or the device to charge the phone, in case that isn't determined automatically by the device.  You might need to look for a similar option and select that you want the phone to charge from the device.

[Teun]

I know it is possible. The adapter does what i need. But I want to understand how it does it.

I think you may have issues due to the fact that the phone will have USB OTG, which is either a host of device - an ethernet interface is a 'device', which the host expects to supply power to.
Not sure if the OTG spec or any USB-C updates have changed this.
Is there a reason you can't use wifi instead of hardwired ethernet? 

Yes that seems to be the problem. Device wants to supply power as it is host, but I need it to accept power while it handles data transfer. As for why no wifi, it's what the client wants.

Now I have been reading about CDP "charging downstream port" and ACA-dock "Accessory Charging Adapter". It seems to me that both of these could help me do that but I'm struggeling to really understand how they work.