AN1992, Isolating RS-232 Interfaces with High-Speed Digital Optocouplers Application Circuit

Application Circuit shows an isolated RS-232 interface using PS9121 optocouplers rated for 3.75kV isolation and up to 15Mbps data rate. Its output supply range is from 2.7V to 3.6V. The RS-232 transceiver ICL3221EF is specified with a data rate of 250kbps and operates from a 3.0V to 3.6V supply. Logic buffers (B) are used to drive the necessary LED currents that usually cannot be provided by low-power MCUs or RS-232 receiver outputs.