Ultrawide support for TBT3-UDC3


I have a 34GP83A-B LG ultra wide that has DisplayPort and HDMI 2.0 inputs. I’m using the dipslayport for another computer, and am using the TBT3-UDC3 with HDMI 2.0. The monitor supports 3440x1440 with 50hz and 85hz, also optionally HDR, via HDMI 2.0. All of these modes seem to work ia the TBT3-UDC3 hdmi out, BUT, I’m getting random signal drop outs.

I tried buying a high quality HDMI 2.1 cable to see if the cable makes a difference, but oddly even though it’s a better cable than the 2.0 cable I’m using now, it doesn’t seem to work at all with the TBT3-UDC3 and LG monitor. This is surprising, as I thought these 2.1 cables should be backwards compatible with a 2.0 device.

I’ve now dropped the system down to 50hz, and it’s maybe seems like I get fewer dropouts. That said, I’d really like to at least get 85hz. Before I buy anymore cables:

  1. Is it reasonable to think that the dock will support this resolution and refresh rate via HDMI 2.0?
  2. The dock definitely supports it via DisplayPort, so if I got a DisplayPort to HDMI cable would that work? The supplied DisplayPort to HDMI adapter doesn’t seem to work well at all, but perhaps a properly rated single adapter cable would?

Hi Alexander,

Thanks for posting!

Based off your report, I understand that while 3440x1440 @ 85Hz/50Hz does work through the TBT3-UDC3, we’re seeing that the LG display flickers in and out occasionally. Additionally, these problems are not observed when connected to the DisplayPort output on the dock. Please let me know if I understand that correctly.

Before advising further here, could you please let me know the specific make and model of the computer you are using?

We’ll be able to better assist from there.

Thanks for giving us a chance to help!


It’s a MacBook Pro 16. I haven’t tried the DisplayPort from the TBT3 as I’m using that port on the monitor for another computer. I have a USB-C to HDMI cable that was working fine direct from the computer before I bought the TBT3. Right now I’m using an HDMI 2.0 cable from the TBT3 to the LG. I also bought a new HDMI 2.1 cable that supports 8k, and that doesn’t work at all from the TBT3 to the LG. I wanted to rule out a bad HDMI cable, but was surprised that the higher quality cable didn’t work at all.

Thanks for the clarification.

We’ve seen issues with the MacBook Pro 16" and HDMI flickering through the TBT3-UDC3 dock, and we have an updated firmware available which has been reported to resolve this problem by several customers. We have a thread about as well: https://support.plugable.com/t/monitor-blinking-on-hdmi-port-of-tbt3-udc3-with-mbp-16/20299

If you have a Windows Thunderbolt 3 or USB-C system (or Bootcamp), could you please follow our firmware update instructions? If you are unable to update the firwmare in the dock, please reach out to us at support@plugable.com with your Amazon Order ID. We’d be glad to provide a warranty replacement updated with the latest firmware.



Thanks, I do have a windows computer but sadly it doesn’t have USB-C. Is there a USB-C to USB adapter that I can use to update the firmware?

edit: would something like this let me update the firmware? https://www.amazon.ca/nonda-Adapter-MacBook-Laptops-Chargers/dp/B0861Y5LF6/ref=sr_1_4?dchild=1&keywords=usb+to+usb-c+adapter&qid=1617640007&sr=8-4

Thanks for asking. Unfortunately, the answer is no – for the firmware utility to work properly, a monitor must be connected to the HDMI port on the dock and the HDMI screen must be recognized by the host computer.

Without a Thunderbolt 3 or USB-C port (that supports USB-C video), the HDMI port would not function. USB 3.0 does not support native video output, and adapters do not provide that functionality I’m afraid.

Could you please reach out to us at support@plugable.com with your Amazon Order ID? We’ll confirm purchase and warranty status and we’d be more than happy to send you warranty replacement flashed with the latest firmware.



The customer reached out to us directly and we sent out a warranty replacement unit flashed with the latest firmware. This resolved the issues and the new dock is working as expected!

I’ll be closing this thread, but for anyone else having similiar issues, please feel free to open up a new topic or contact us directly at support@plugable.com. We’re glad to help.

Best wishes,