The LM117 die has four connections, Vin, Vout, ADJ, and sense. What do you do with sense connection?
The sense pad is the Vout sense pad and it (as well as the back of the die) gets connected to Vout. It is bonded out separately so that changes in load current will affect only the drop in bond wires to the power device and the sense line will maintain the voltage at the point where it is connected constant. Two things can happen if sense connection is left floating: 1. The most likely occurance is that there is a connection through the substrate from Vout sense to Vout. In this case any drops in the Vout bondwire will not be compensated for. This could result in Load Regulation values of over 20mV depending on size of bond wire and load. 2. Vout sense is isolated from Vout. In this case we would not expect the part to regulate at all. It could oscillate, go to a rail or sit at some arbitrary voltage depending on the die parasitics.
