I/O protection under over-voltage and back-drive conditions by single well charging
AssigneeNational Semiconductor Corporation
InventorsWeiye Lu, Elroy M. Lucero, Khusrow Kiani
Life of this patent
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Abstract
In an I/O driver that includes a cascoded pair of PMOS driver transistors connected to a pair of cascaded NMOS driver transistors and that defines a pad output between the PMOS and NMOS driver transistors, a method of providing the CMOS I/O driver with over-voltage and back-drive protection includes providing circuitry for charging the wells of the PMOS transistors either to VDDIO during normal voltage mode by making use of the power supply, or to a common voltage during over-voltage and back-drive operation using the pad voltage.
Claims12
A method of providing a CMOS I/O driver with over-voltage and back-drive protection, the I/O driver including a cascoded pair of PMOS driver transistors connected to a pair of cascoded NMOS driver transistors and defining a pad output between the PMOS and NMOS driver transistors, the method including
- providing circuitry for charging the wells of the PMOS transistors to a common voltage during over-voltage and back-drive operation, and
- defining a first NMOS gate voltage (NG1) during back-drive operation by providing a pad input and one or more voltage drops to define NG1, and providing a first switch (SW1) that is operable to close when NG1 exceeds VDDIO by a predefined amount.
Dependencies are inferred from the claim text.