The DG458 and DG459 are 8-channel single-ended and 4-channel differential analog multiplexers, respectively, incorporating fault protection. A series n-p-n MOSFET structure provides device and signal-source protection in the event of power loss or overvoltages. Under 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 following it, but also protects the sensors or signal sources which drive the multiplexer.