Help getting laptop to display more than 30 Hz on external monitor

[adorablebob]

Issue: My laptop only displays 30 Hz as an option at my monitors native resolution 3840 x 1600

This is my setup:

Dell Latitude 7490 (laptop) connected via USB-C to WD19S (dock). HDMI 2.1 cable going from dock to LG 38GN950-B (monitor)

The laptop has an Intel UHD Graphics 620 iGPU, and i5 8250U CPU.

I've checked the spec's of my laptop, the dock, the cables, and my monitor, and they all seem to suggest that I should be able to get more than 30 Hz at 3840 x 1600, unless I'm reading something wrong.

Any suggestions?

[MUC]

This seems to be a bandwidth bottleneck caused by the dock. UHD620 can provide 4096 x 2304 @ 60Hz over DisplayPort (version 1.2 | HBR2 bandwidth = 21.6 Gbps). The laptop features 1x USB-C 3.0 with DisplayPort 1.2.

If 3840 x 1600 @ 60Hz is not possible with the existing configuration, I assume the connection is operating in DisplayPort Alt Mode. This explains the limit because in DP HBR2 Type-C Alt Mode via 2 lanes the bandwidth is halved. Therefore only 3840 x 1600 @ 30 Hz are possible.

To get the desired resolution and refresh rate you'd have to disconnect any device from the dock except the monitor to make 4 lanes available for video transport.

[n_scott_pearson]

When the connected device is utilizing both USB (and this will be the case for a Dock regardless of whether any USB device are connected) and the embedded DisplayPort 1.2 stream, the video bandwidth is cut in half. This means 4K@30Hz is the best you will do. 4K@60Hz is only possible when the USB-C port is used exclusively for video connection.

Sorry,

...S

[adorablebob]

Thanks for the info. When you say "4K@60Hz is only possible when the USB-C port is used exclusively for video connection" do you know if getting a USB-C to HDMI 2.0 cable/adapter would work as an alternative to skip the dock?

[n_scott_pearson]

Yes, that's exactly what I meant. Connecting monitor using a USB-C-to-DisplayPort or a HDMI 2.0-compliant USB-C-to-HDMI adapter (or cable) will allow you get 4K@60Hz.
...S