The TMUX582F-SEP detects overvoltage inputs by comparing the voltage on a source pin (Sx) with the fault supplies (V_FP and V_FN). V_FN must be set to GND. A signal is considered overvoltage if it exceeds the fault supply voltages by the threshold voltage (V_T).

When an overvoltage is detected, the switch automatically turns OFF regardless of the logic controls. The source pin becomes high impedance and allows only a small leakage current 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) is pulled to the supply that was exceeded. For example, if the source voltage exceeds V_FP, the drain output is pulled to V_FP. The pull-up impedance is approximately 40kΩ, and as a result, the drain current is limited to roughly 1mA during a shorted load (to GND) condition.

Figure 8-1 shows a detailed view of how the pullup/down controls the output state of the drain pin under a fault scenario.

Figure 8-1 Detailed Functional Diagram

V_FP and V_FN are required fault supplies that set the level at which the overvoltage protection is engaged. V_FP can be supplied from 3V to V_DD, while the V_FN must be set to GND. If the fault supplies are unavailable in the system, the V_FP pin must be connected to V_DD, while the V_FN pin must be set to GND. In this case, overvoltage protection then engages at the primary supply voltage V_DD.