The +5_EXT signal is for powering small external circuits. This signal comes from the +5V DC input to the display module and is routed through a PTC resettable fuse. The PTC has a rating of 2A at 20C or 1.5A at 60C, and this is the power budget for the combined total of all +5V_EXT outputs. Also, each individual +5_EXT pin is limited to 1A max.