High current drain-to-gate clamp/gate-to-source clamp for external power MOS transistors

A method for protecting the gate oxide in an external transistor, comprising the steps of:

• determining when the voltage between the gate and one of the source/drain terminals of the external transistor exceeds a first threshold voltage;
• conducting current between the gate and the one of the source/drain terminals of the external transistor through a first current path, having active devices associated therewith and a high voltage side and a low voltage side, when the voltage has been determined to exceed the first threshold voltage and preventing the voltage thereacross from rising substantially above the first threshold voltage;
• determining when the current through the first current path exceeds a predetermined bypass current threshold;
• and
• bypassing the current around the first current path having the active devices therein through a second bypass current path such that the current through the first current path is limited to a predetermined level.

A circuit, comprising:

• a first transistor having gate, source, and drain terminals;
• a first threshold circuit having a first terminal coupled to said drain terminal of said first transistor and a second terminal;
• a first impedance coupled between said second terminal of said first threshold circuit and said gate terminal of said first transistor;
• a first current bypass transistor having a source/drain current path coupled between said gate and drain terminals of said first transistor and a gate coupled to a node between said first threshold circuit and said first impedance;
• wherein said first threshold circuit blocks current when a voltage at said drain terminal of said first transistor is less than a first threshold voltage and conducts current to turn said first transistor on when the voltage at said drain terminal of said first transistor exceeds said first threshold voltage and said first current bypass transistor turns on to bypass a portion of the current through said first threshold circuit when the current through said first threshold circuit exceeds a first current threshold.