I have a UFP device (basically just a light) that I am trying to sink for power only. The "light" has a micro-B plug, which then plugs into a micro-B port on a PCB, that then includes a USB-C plug which plugs into a USB-C port on the Samsung mobile phone.
I believe the PCB is to USB-C spec and seems to work properly with multiple devices. I've tried laptops, tablets, mobiles phones, etc. The only devices that do not want to work properly seem to be Samsung mobile phones, such as a Galaxy S8.
When plugged into a Galaxy S8, power is applied at about 1 second on, 1 second off, a total of 6 times, then the S8 no longer sends power. If the sink remains plugged in, the notifications on the S8 show "USB device connected" and then "USB device disconnected" multiple times, even after power is no longer sent from the phone.
The CC pin is grounded with a 5.1k ohm pull-down resistor and also has a 56k ohm pull-up to VBUS.
If I remove the 56k ohm pull-up resistor, the Samsung S8 sends power and the UFP device functions properly. However, the 56k pull-up obviously needs to be there for safety, in case someone decides to try to use the adapter for a charging cable (even though that is not the intention of the adapter). Or am I over thinking it? Can I just pull the 56k and roll with it?
What is it that these Samsung devices are looking for that other devices are not looking for? Or is there something I'm just not seeing, or that is not compatible?
And a side question: Is a device required to be OTG compatible in order to host for a UFP? I ask this because I have tested with another device that will not act as a host, no matter what configuration I use. This device is not OTG compatible though.
Hopefully my post is clear enough and any insight is much appreciated.
Best Answer
No, this is not how it is intended to work. It is either pull-up, or pull down, which determines the role of Samsung port. "Safety" has nothing to do with this.
If you have a cable (or device) with 56k Rpu, then the port identifies the plug as other USB host (with standard default power capability). The phone will behave as a device, sinking power from VBUS and possibly charging itself.
If you have the cable/device with 5.1k pull down, the phone port with identify the plug as peripheral USB device, and will supply VBUS.
You can't have both Rpu and Rpd on the same pin at once, it will be confusing for the phone.