The TMUX7308F and TMUX7309F detect overvoltage inputs by comparing the voltage on a source pin (Sx) with the supplies (V_DD and V_SS). A signal is considered overvoltage if it exceeds the supply voltages by the threshold voltage (V_T).

When an overvoltage is detected, the switch with the overvoltage automatically turns OFF, and stays OFF regardless of the logic controls. The source pin becomes high impedance and allows only a small leakage current to flow through the switch and the overvoltage does not appear on the drain. When the overvoltage channel is selected by the logic control, the drain pin (D or Dx) is pulled to the supply that was exceeded. For example, if the source voltage exceeds V_DD, the drain output is pulled to V_DD. If the source voltage exceeds V_SS, the drain output is pulled to V_SS. The pull-up impedance is approximately 40 kΩ, and as a result, the drain current is limited to roughly 1 mA during a shorted load (to GND) condition.

Figure 10-3 shows a detailed view of the how the pullup/down controls the output state of the drain pin under a fault scenario.

Figure 9-1 Detailed Functional Diagram