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.

Micro-B to USB-C Adapter

Micro-B PCB

![USB-C Plug PCB - Side 1

![USB-C Plug PCB - Side 2

DFP/UFP Schematic per USB.org

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.

  • \$\begingroup\$ I have a Galaxy S8 phone, and love it. The USB-C port behaves as it should with all I have plugged into it. PC, flash memory stick, etc. Something is miss-wired. \$\endgroup\$
    – user105652
    Commented Mar 23, 2018 at 23:03
  • \$\begingroup\$ For sure. I'm not saying the Samsung is in the wrong. I just don't understand why everything else works with this setup, aside form Samsung phones. Removing the 56k pull-up makes perfect sense, but why does everything still work with it in place? \$\endgroup\$ Commented Mar 26, 2018 at 19:48
  • \$\begingroup\$ Nothing is clear. Please answer: (1) is your light a source, or a consumer? (2) what do you expect from your Samsung phone? \$\endgroup\$ Commented Mar 26, 2018 at 19:49
  • \$\begingroup\$ The light is intended to only be a sink for power from the device. It's not necessarily that I expect anything from the Samsung device. It is more about why Samsung devices are the only devices among all tested to behave differently. \$\endgroup\$ Commented Mar 26, 2018 at 19:59

1 Answer 1


However, the 56k pull-up obviously needs to be there for safety,

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.

  • \$\begingroup\$ If I understand correctly, I can pull the 56k, leave the 5.1k and there is nothing to worry about? \$\endgroup\$ Commented Mar 23, 2018 at 22:49
  • \$\begingroup\$ And What's all this ado about incorrectly configured cables ruining laptops and all of that? Would this not apply to what I'm doing then? \$\endgroup\$ Commented Mar 23, 2018 at 22:55
  • \$\begingroup\$ @TravisThomas, sorry, I was unable to follow the complexity of your setup and multitude of plug options, so I can't say more than I said. If you want your lamp to sink current from Type-C port, you need to have 5.1k pull-down in your cable (or on lamp end). \$\endgroup\$ Commented Mar 23, 2018 at 22:57
  • \$\begingroup\$ Thanks for the information and it does make sense that it needs one or the other. I do have one question about this though. Why does it work as is with everything else I've tried (laptops, other phones, etc.)? Why would Samsung phones be the only thing that doesn't work? How do these other devices "know" to provide power, rather than try to take it? \$\endgroup\$ Commented Mar 26, 2018 at 19:33
  • \$\begingroup\$ @TravisThomas, I can only speculate that "everything else" has a sloppy Type-C design. You need to be more specific. \$\endgroup\$ Commented Mar 26, 2018 at 19:46

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