Circuit and method for transistor turn-off with strong pulldown
AssigneeTexas Instruments Incorporated
InventorEric Labbe
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Abstract
In accordance with the present invention, there is provided a circuit and method for providing a switchable strong pulldown for a power FET in an off state to avoid inadvertent or false turn ons. A strong pulldown is provided to the gate of a power FET to avoid inadvertent turn on during output swings. In other cases, the gate of the power FET is pulled down weakly to reduce EMI and voltage noise in the circuit. In a particular exemplary embodiment, the present invention provides a circuit and method for obtaining a strong pulldown on the gate of a power FET in an off state, while providing a weak pulldown during turn on to turn off transitions. The invention avoids false turn ons during fast output transitions while maintaining relatively high EMI protection.
Claims11
A driver circuit for controlling a power FET, comprising:
- a low impedance FET coupled to a gate of the power FET for providing a low impedance path to a reference voltage for the gate of the power FET when the low impedance FET is in a conductive state;
- a control circuit coupled to the low impedance FET and operable to turn the low impedance FET on and off;
- and
- an enable signal in the control circuit operable to enable a conductive state for the low impedance FET when a gate voltage of the power FET transitions through a predetermined threshold.
A method for driving a power FET, comprising:
- transitioning the power FET from an on state to an off state;
- applying a strong pull down to the gate of the power FET to maintain the power FET in an off state;
- transitioning the power FET from an off state to an on state;
- and
- removing the strong pull down from the gate of the power FET to permit the power FET to transition to the on state.
A circuit for driving a power FET, comprising:
- a switch connected to a gate of the power FET for providing a strong pull down on the gate when the switch is turned on;
- an enable signal for the switch, operable to turn the switch on after an interval when the power FET begins to turn off.
Dependencies are inferred from the claim text.