Under-voltage lockout programming on Delta D12F200 DC/DC converter
I would interpret the equation to mean Ven as the underlocking voltage, then find Ren. 

So if I wanted the underlocking voltage to start at 5V, 

\$ R_{en} = \frac{315}{14*(5)+3.8} = 4.26\$

At this point I would assume they mean 4.26 kiloohms, but this is not clear, you could experiment with the device and turn down a lab supply below the 5V limit and see if the device shuts off, and that would confirm the intuition.

But really, this datasheet is crap. There is no other information at all in the datasheet and no nice example table like there is for Rtrim. I would complain loudly to the manufacturer. They would be the best resource to clear this up, and they need to fix their datasheet.