| 摘要 |
PURPOSE:To ensure sufficient protecting operation even against a positive surge voltage and to obtain an input protecting circuit having desirable characteristics for three-value control input, by providing a protecting circuit having a diode whose anode is connected to an input node and a capacitor connected between the cathode of the diode and a potential supply source. CONSTITUTION:One end of an input protecting resistance R1 is connected to an input pad 11 while to the other end there are connected an end of another input protecting resistance R2, the cathode of an input protecting diode D whose anode is grounded at a grounding point and the anode of an input protecting diode D2. A capacitor C1 is connected between the cathode of the diode D2 and the grounding point, while the gate of a MOS transistor Q1 constituting an internal circuit is connected to the other end of the resistance R2. If a positive surge voltage is applied as an input voltage, the diode D2 is forwardly biased and current by the surge voltage flows into the capacitor C1. The larger a value of capacitance is, the more the input voltage is clamped. Thus, decreased stress is applied to the gate of the MOS transistor Q1 in the internal circuit. |
