LINE-POWERED INTEGRATED CIRCUIT TRANSCEIVER

摘要

An integrated circuit provides a low-power RS232 interface . Positive power supply provides a positive source for positive level transmission at (TXOUT). A zero-power comparator circuit (310) selects between ground and the received signal (RXIN) to provide a negative power supply for negative level transmission (TXOUT). For ESD protection, the input pad (RXIN) is connected to split series resistor (RP2) with clamping diodes of different types. When a positive-going transient appears at the pad (RXIN), moderate impedance limits current; when a negative-going transient appears, higher impedance limits current. Comparator (310) is not complementary and has a common mode range, to control switching of an output driver (120) between ground and an incoming signal (RXIN). Separate power supplies (Vcc and Vdrv) supply internal logic (140, 130) and output driver (120). If a power supply fails, floating nodes in the logic elements are clamped and excessive current drain is avoided. A series resistor and its parasitic bipolar device in a well tie (NWELL) permit clamping with reduced current consumption.