The HI-506A, HI-507A, HI-508A and HI-509A are analog multiplexers with active overvoltage protection. Analog input levels may greatly exceed either power supply without damaging the device or disturbing the signal path of other channels. Active protection circuitry assures that signal fidelity is maintained even under fault conditions that would destroy other multiplexers. Analog inputs can withstand constant 70VP-P levels with 15V supplies. Digital inputs will also sustain continuous faults up to 4V greater than either supply. In addition, signal sources are protected from short circuiting should multiplexer supply loss occur. Each input presents 1k of resistance under this condition. These features make the HI-506A, HI-507A, HI-508A and HI-509A ideal for use in systems where the analog inputs originate from external equipment, or separately powered circuitry. All devices are fabricated with 44V dielectrically isolated CMOS technology. The HI-506A is a single 16-channel multiplexer, the HI-507A is an 8-channel differential multiplexer, the HI-508A is a single 8-channel multiplexer and the HI-509A is a differential 4-channel multiplexer. If input overvoltage protection is not needed the HI-506/507/508/509 multiplexers are recommended. For further information see Application Note AN520.