Patent ID: 8824111
Filing Date: 2014-09-02
Classification: H01L,H03K

Abstract:
1. A circuit for protecting a node in an electronic device from an electrostatic discharge comprising: a voltage rail arranged to provide a predetermined voltage when the device is powered; a first switching device connected between said node and ground; a second switching device connected between the node and the gate or base of the first switching device and arranged to control the conductance of the first switching device between said node and ground, the gate or base of the second switching device being coupled to the voltage rail; a third switching device connected between the base or gate of the first switching device and ground; a fourth switching device and a resistor connected in series between the node and ground so as to form a potential divider, the fourth switching device having its base or gate connected to the voltage rail; a voltage inverter receiving as its input the output of the potential divider and providing its output at the base or gate of the third switching device; wherein, the second switching device is configured to, irrespective of whether the device is powered or not powered, (a) hold the conductance of the first switching device low when the potential difference between the node and the voltage rail is within an operating range, and (b) hold the conductance of the first switching device high in response to an overvoltage at the node so as to allow current to flow from the node to ground, and the third switching device is configured to, when the device is powered, hold the conductance of the first switching device low when the potential difference between the node and the voltage rail is within the operating range, and, when the device is not powered, hold the conductance of the first switching device high in response to an overvoltage at the node.