The TBU^® device is a silicon-based, solid-state, resettable device which is placed in series with a signal path. The TBU device operates in approximately 1µs (tblock) once the line current exceeds the TBU device’s trip current (I_trip). When operated, the TBU device restricts line current to less than 1mA (I_Q), typically, and will block all system voltages and any other voltages including the surge up to rated limits. After the surge, the TBU device resets when the voltage across the TBU device falls to the V_RESET level. The TBU device will automatically reset on lines which have no DC bias or have DC bias below V_RESET (such as unpowered signal lines). If the line has a normal DC bias above V_RESET, the voltage across the TBU device may not fall below V_RESET after the surge. In such cases, special care needs to be taken to ensure that the TBU device will reset, otherwise an automatic or manual power down will be required.