Latitude 5590 & LG Ultrafine 4K via USB-C

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@garrytrinder  What exact LG display model do you have?  There are a few different ones under the "UltraFine 4K" moniker, and some of them are actual Thunderbolt 3 displays, not USB-C.  In that case, connecting with a Thunderbolt 3 cable (which isn't the same as a USB-C cable) won't work if your system doesn't have Thunderbolt 3.  However, if your display also has a DisplayPort input, you could get a USB-C to DisplayPort cable to make it work.  That setup would prevent you from getting power or USB data from the display though.

@garrytrinder  Wanted to build on my previous reply a bit to offer a somewhat better solution if you do in fact have a Thunderbolt 3 display and provide a bit of clarification.

If the display is Thunderbolt 3 but you want to be able to draw power from it, this adapter will allow you to connect a DisplayPort cable between the adapter and display for video, and then you can connect the TB3 cable from the display into that adapter's power passthrough port for power.  So you'll have two cables running between the adapter and your display, but still only one thing to plug into your laptop -- and then you'll have video and power.  But even with that adapter you still won't have a USB data path to the display, which means you wouldn't be able to use any USB ports built into the display or the audio output that's working for you right now.

Speaking of that audio output, I suspect the reason that's working is because USB-C and TB3 cables have pins within the connector dedicated to USB 2.0 data, so it's possible that the audio controller built into the display interfaces over USB 2.0 rather than Thunderbolt 3.  I wouldn't have guessed that, but if it is in fact a TB3 display and you have a non-Thunderbolt system and yet audio is working, that's the only way I can think to account for that result.

If you do need a USB data path between your Latitude and LG display, then the only way that would be achievable with a non-Thunderbolt system would be if the display offered an "upstream" USB port.  That would be either a USB-B port, as found on many printers, or possibly a non-Thunderbolt USB-C port specifically meant to be connected to a host PC rather than meant to be used for connecting USB-C peripherals.  If your display has one of those ports, you can get a USB-B to USB-A cable (otherwise known as a "regular USB cable") or a USB-C to USB-A cable to connect that port to one of the USB-A "regular USB" ports on your Latitude.  In either case, make sure the cable you get supports USB 3.0, because even among USB-C to USB-A cables, there are some that only support power and USB 2.0 data speeds.  But if your display doesn't have one of those ports to create a USB data path without Thunderbolt, then unfortunately you'd be stuck.

Thank you for the reply @jphughan , much appreciated.

What exact LG display model do you have?

The model I have is 24MD4KLB.

However, if your display also has a DisplayPort input, you could get a USB-C to DisplayPort cable to make it work.

The manual states ThunderboltTM 3( ) / USB-C Host (Mac) connection port x 2, USB expansion port x 3 in the Input Connector specification and the following notes

• PD (Power Delivery) is supported via ThunderboltTM 3( ) / USB-C Host (Mac) port.
• Features may not work properly depending on the connected device’s specifications and the environment.
• ThunderboltTM 3( ) / USB-C Host (Mac) port is not for the Monitor Power source but for a PC power source. Connect the Power cord to supply power to the Monitor.
• Make sure to use supplied cable. Otherwise, this may cause the device to malfunction.
• The charging speed may vary depending on the port and device.
• ThunderboltTM 3( ) / USB-C Host (Mac) is supported in such environments as Windows 10 and Mac product.
• In accordance with Mac products may not support the recommended resolution or the some features.
• The ability to set up dual monitors using the ThunderboltTM 3 ( ) and daisy-chaining technology depends on the performance of your video card.
• Some USB devices and USB-C monitors may behave abnormally when connected to ThunderboltTM 3( ) / USB-C Host (Mac) ports.

There is no DisplayPort on the monitor or on the Latitude, on the Latitude the USB-C port provides DisplayPort over USB-C, so the adaptor you mention would not work in this scenario.

My main use case for this monitor is just for video use, sound, power & data transfer is very much a bonus but not critical to my setup.

@garrytrinder  Funny, I remember somebody else just asking about that exact display.  In their case it didn't work because they had plugged their cable into a USB-C expansion port rather than one of the host ports because they assumed that the host ports were only for Thunderbolt-capable systems.  But if you're already plugged into a host port, then this should be plug and play.  The only POTENTIAL thing I can think of is that if you happen to have an "active" Thunderbolt 3 cable, which can be desirable because it allows for longer cables (at much higher expense), then those cables when used with regular USB-C ports typically only work as USB 2.0 and power cables, which means they would not carry video over regular USB-C.  But most TB3 cable are passive and do work as USB 3.x + video cables even in regular USB-C mode.  And the note in the manual says to use the cable that came with the display, so if that's what you have, I'm going to guess that it supports both USB-C and TB3 given that the display itself explicitly supports both types of hosts.

Have you updated your GPU drivers and BIOS/firmware?

@garrytrinder  Fantastic! Thanks for reporting back too. Out of curiosity what cable were you using before? Was it the cable that came with the display? If so I’d be surprised LG would ship a display that supports both USB-C and TB3 and bundle a cable that only works for TB3 hosts. The even stranger part is that I almost didn’t bother theorizing about the cable. There aren’t very many “active” TB3 cables out there, partly due to cost — a TB3 cable that uses active circuitry to support 40 Gbps across 6 feet costs about $60 as of this writing — so I seriously doubted that would be the issue. Most TB3 cables work perfectly fine as USB-C cables, including supporting video. But I’m glad I wrote all that up!

Just be aware that if your display is running 4K at the normal 60 Hz, then your USB data speeds for anything you plug into the display will be limited to USB 2.0. That’s just how USB-C works with systems that only support DisplayPort 1.2/HBR2 over USB-C.

Congrats on your success!

Out of curiosity what cable were you using before?

I was using the cable supplied by LG that came in the box, my assumption is that it is a TB3 cable as it has the lightning bolt symbol which matches the host port on the back of the monitor.

Just be aware that if your display is running 4K at the normal 60 Hz, then your USB data speeds for anything you plug into the display will be limited to USB 2.0. That’s just how USB-C works with systems that only support DisplayPort 1.2/HBR2 over USB-C.

Noted, as it happens I am using the ports on the laptop for connecting peripherals so I don't have anything connected to the monitor except for my MacBook which is sat happily charging from the remaining TB3 host port

Thanks again for your detailed responses

@garrytrinder  Very strange indeed.  I'm not surprised that LG shipped a Thunderbolt cable, but I am definitely surprised that they shipped a "Thunderbolt-only" cable given that their documentation not only covers connecting to USB-C hosts, but even specifically says to use only the cable provided with the display!  Oh well.  Glad you're sorted, and happy to help!

@garrytrinder​ 

I am very very confused by this.

I have a dell vostro laptop for work use.

I have this monitor at home; https://www.lg.com/de/monitore/fhd-qhd/27md5kl-b/

(LG ultrafine) I have used a standard USB-C cable purchased and this does not work. As you said there is no Video showing but there is Audio connection so it is showing as a device.

Does this monitor require an extremely specific USB-C cable with this Thunderbolt 3 capability 40 Gbps? If I get this cable (which is expensive) will this let me connect to this incredibly complicated monitor with my dell laptop?

I have tried a number of different USB-C cables now with the screen but it seems I need this very specialist cable first.

Please help!!!!!