The three USB-C ports on the display provide additional connectivity to USB 3 devices only.

The LG UltraFine 5K Display doesn't support daisy-chaining of Thunderbolt 3 devices or displays. If you don't have it, you can use a Thunderbolt 3 cable capable of delivering 5A of power. If you don't see an image after connecting the LG UltraFine 5K Display to your Thunderbolt 3-equipped Mac, make sure that you're using the cable that came with the display. If you have issues connecting the display To charge Apple Lightning-based devices and accessories - such as iPhone, iPad, AirPods, Magic Keyboard, Magic Trackpad 2, and Magic Mouse 2 - you can use the Apple USB-C to Lightning Cable or a combination of the Apple USB-C to USB Adapter and the Apple Lightning to USB Cable. The LG UltraFine 5K Display provides 7.5W to each of its three downstream USB-C (5 Gbps) ports. If you're using this adapter, you need to also connect your Mac to power using the power supply it came with. Power isn't delivered from the display to your Mac when you connect with the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter. The LG UltraFine 5K Display provides up to 85W of power over USB-C and will fully power MacBook Pro (2016 and later) and MacBook Air (Retina, 13-inch, 2018) using the included Thunderbolt 3 (USB-C) cable. With the Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter and a Thunderbolt cable, you can use the LG UltraFine 5K Display at 4K and lower resolutions with these Mac models:

You can use the LG UltraFine 5K Display with these Mac models at full 5K resolution: Compatible Mac models are grouped below by the resolutions that they support. The LG UltraFine 5K Display requires a compatible Mac running macOS Sierra 10.12.1 or later (macOS Sierra 10.12.2 or later is recommended). System requirements and compatible Mac models The display has three downstream USB-C ports (5 Gbps) that offer additional connectivity and power to compatible devices and accessories.

When you connect the display using a single Thunderbolt 3 cable (included), it provides up to 85W of charging power to your MacBook Pro with Thunderbolt 3 (USB-C) ports. Integration with macOS lets you control your display's volume and brightness without the need for physical buttons on the display. The 27-inch LG UltraFine 5K Display features a 5120 x 2880 resolution, a P3 color gamut, 500 cd/m2 of brightness and built-in stereo speakers, camera, and microphone.

Mac doc on center monitor