On the EOS 80D, Live View should normally remain on much longer than just a few seconds—typically up to around 30 minutes under normal conditions. If it is shutting off almost immediately, the most likely causes mentioned are:

• a low battery, or
• the camera getting too warm internally.

So first try a fully charged battery, and make sure the camera isn’t overheating from extended use or a hot environment. If both battery level and temperature are normal, the behavior is not typical and may indicate a camera setting you’ve overlooked or a possible fault.