Circuit and method for protecting input/output stage of a low voltage integrated circuit device from a failure of the internal power supply or in the power-up sequencing of power supplies

A computer system comprising:

• an integrated circuit;
• an external power supply providing voltage to the integrated circuit;
• a protection circuit within the integrated circuit having associated therewith a maximum terminal voltage difference, which, if exceeded, causes failure of the protection circuit;
• a power supply circuit within the integrated circuit coupled between the protection circuit and an internal power supply provided within the integrated circuit comprising a first p-channel field effect transistor having a first known resistance between a source terminal and a drain terminal when the first p-channel field effect transistor is in a first known state, and having a bulk terminal coupled to a source terminal;
• a pass circuit within the integrated circuit coupled to the protection circuit and to the power supply circuit at a common node and comprising a second p-channel field effect transistor having a second known resistance between a source terminal and a drain terminal when the second p-channel field effect transistor is in a second known state, and having a bulk terminal coupled to a source terminal, and wherein the pass circuit cooperates with the power supply circuit to reduce a terminal voltage difference across the protection circuit by an amount not limited by the gate-source voltage of the first p-channel field effect transistor, and by an amount not limited by the gate-source voltage of the second p-channel field effect transistor, in the event of failure of the internal power supply;
• and
• a variable voltage supply circuit within the integrated circuit coupling the pass circuit to the external power supply.

A method of reducing a terminal voltage difference in a protection circuit within an integrated circuit in the event of failure of an internal power supply within the integrated circuit comprising:

• coupling a power supply circuit within the integrated circuit between the protection circuit and the internal power supply, the power supply circuit comprising a first p-channel field effect transistor having a first known resistance between a source terminal and a drain terminal when the first p-channel field effect transistor is in a first known state, and having a bulk terminal coupled to a source terminal;
• coupling a pass circuit within the integrated circuit to the protection circuit and to the power supply circuit at a common node, the pass circuit comprising a second p-channel field effect transistor having a second known resistance between a source terminal and a drain terminal when the second p-channel field effect transistor is in a second known state, and having a bulk terminal coupled to a source terminal, and wherein the pass circuit cooperates with the power supply circuit to reduce a terminal voltage difference across the protection circuit by an amount not limited by the gate-source voltage of the first p-channel field effect transistor, and by an amount not limited by the gate-source voltage of the second p-channel field effect transistor, in the event of failure of the internal power supply;
• and
• coupling a variable voltage supply circuit within the integrated circuit to an external power supply provided from outside the integrated circuit.