Fail-safe logic circuitry allows voltages on the logic control pins to be applied before the supply pins, protecting the device from potential damage. The switch is specified to be in the OFF state, regardless of the state of the logic signals. The logic inputs are protected against positive faults of up to +44 V in the powered-off condition, but do not offer protection against the negative overvoltage condition.

Fail-safe logic also allows the TMUX7308F and TMUX7309F devices to interface with a voltage greater than V_DD during normal operation to add maximum flexibility in system design. For example, with a V_DD of = 15 V, the logic control pins could be connected to +24 V for a logic high signal which allows different types of signals, such as analog feedback voltages, to be used when controlling the logic inputs. Regardless of the supply voltage, the logic inputs can be interfaced as high as 44 V.