The LM3940 is a 1A low dropout regulator designed to provide 3.3V from a 5V supply. The LM3940 is ideally suited for systems which contain both 5V and 3.3V logic, with prime power provided from a 5V bus. Because the LM3940 is a true low dropout regulator, it can hold its 3.3V output in regulation with input voltages as low as 4.5V.
The T0-220 package of the LM3940 means that in most applications the full 1A of load current can be delivered without using an additional heatsink.