The rapid, widespread use of 3.3V logic circuits complicates the selection of RS232 interface circuits. In these systems, an RS232 interface chip which uses the 5V supply for charge pump and driver operation and the 3V supply for receiver output levels, provides the best performance. Systems with only a 3V power supply are unable to use 5V powered RS232 interface circuits. Charge pump triplers (or quadruplers) have losses too great for generating RS232 voltage and current levels from a 3.3V supply. Battery-powered 3V systems can use the RS232 transceiver’s SHUTDOWN and Driver Disable controls to maximize battery charge life.
Get more information about Circuit Diagram for 3.3V RS232 Interface System by Gary Maulding in the following article. (source: linear.com)