UCC14240EVM-052: How can I disable the -5V negative output rail on the EVM?

Hello,

Yes, UCC14240 can have a single output. Please refer to calculator on ti.com, and it provides how to modify the board. 

You can also check the app note here and pay attention to the configuration below. The key point is that on the EVM, you will need to remove the FBVEE resistors and short the FBVDD to FBVEE (best to make the short directly at the IC pins by dropping a solder connection across pins 33 to 34). In the schematic below, the RMIL (R1) is shown connected to VDD but you can simply remove RLIM and leave the pin floating for single output configuration.

Steve