The MAX3748A has ESD protection on the DISABLE and LOS pins, the MAX3748 does not.
The MAX3748 is designed to fit an old application where the LOS output would be connected to a 5V part with pull-up resistors to 5V. With the MAX3748A this would be a problem because the ESD diodes to Vcc (3.3V) inside the part would be activated by the external pull-up resistors to 5V. For the MAX3748 this is not a problem.
The MAX3748H is a Hybrid lead-free package version of the MAX3748 and is the only remaining available part.