The ADG438F/ADG439F are CMOS analog multiplexers, the ADG438F comprising 8 single channels and the ADG439F comprising four differential channels. These multiplexers provide fault protection. Using a series n-channel, p-channel, nchannel MOSFET structure, both device and signal source protection is provided in the event of an overvoltage or power loss. The multiplexer can withstand continuous overvoltage inputs from 40 V to +55 V. During fault conditions, the multiplexer input (or output) appears as an open circuit and only a few nanoamperes of leakage current will flow. This protects not only the multiplexer and the circuitry driven by the multiplexer, but also protects the sensors or signal sources which drive the multiplexer.