Semiconductor device having semiconductor element becomes operable when connected to external power source

Abstract

The semiconductor of the present invention comprises: a buffer circuit (40) which operates by the supply of a first power source potential VDD1, and an N-type MOSFET (10) connected between a pad (20) pulled up to a second power source potential VDD2 and a ground. An output line (42) of the buffer circuit (40) is connected to a gate of the N-type MOSFET (10). The semiconductor further comprises a potential setting circuit (50) which sets a potential of the output line (42) of the buffer circuit (40) to a level lower than the threshold level of the N-type MOSFET (10) when the supply of the first power source potential VDD1 is shut off. This potential setting circuit (50) has a first and a second N-type MOSTETs (60, 70) which are connected in parallel between the output line (42) of the buffer circuit (40) and the ground. The first N-type MOSTET (60) has a gate connected to the output line (42) and functions as a forward diode. The second N-type MOSFET (70) has a gate connected to the pad (20) and is made conductive by a rise in the potential of the pad (20) to make the potential of the output line (42) to be the ground potential.

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