These are truly amazing low dropout voltage regulators that output a voltage at 5 volts for the MAX603 and 3.3 volts for the MAX604.
What's so amazing about these regulators is that the dropout is very low as can be seen from the tests I did. What that means is, you can give it a voltage very close to its output voltage and is great for battery use as well.
The maximum voltage that you can give this voltage regulator is 11.5 volts and will accept voltages as low as 2.7 volts. The regulator will also allow 500mA current maximum which is fine for most digital electronics applications. You even have control of the output voltage other than its default by using resistors for an output range of 1.25 to 11 volts. The chip also has protection for thermal overload and reverse current.