Circuits and method for controlling transient fault conditions in a low dropout voltage regulator

A voltage regulator comprising:

• a control loop circuit for balancing an active load current in an error amplifier of a voltage regulator resulting from removal of a transient fault conditions applied to an input terminal or output terminal of the voltage regulator, the control loop circuit comprising:
• a transient fault sense circuit configured to be in communication with a pass transistor of the voltage regulator for determining that the voltage regulator is responding to input or output transient faults and generating a transient fault indicator signal indicating that the voltage regulator is responding to input or output transient faults;
• and
• a local control loop connected to an output terminal of the transient fault sense circuit configured to receive the transient fault indicator signal communicating that the voltage regulator is responding to input or output transient faults;
• wherein the control loop circuit is configured such that when the transient fault indicator signal indicates that the voltage regulator is responding to input or output transient faults, the local control loop clamps an output of a differential amplifier within the error amplifier at a voltage level approaching an operating level, while a pass transistor of the voltage regulator is maintained in deep triode region of operation for insuring fast response in controlling the gate of the pass transistor.

A method for overshoot reduction for minimizing or eliminating an overshoot at an output terminal of a voltage regulator resulting from a transient fault conditions applied to an input terminal or output terminal of the voltage regulator, comprising the steps of:

• activating the voltage regulator;
• monitoring an input voltage at the input terminal or a current at the output terminal of the voltage regulator to sense if there is a transient fault condition;
• providing a Miller capacitance at the output terminal of a differential amplifier within the voltage regulator to prevent the output of the differential amplifier from being discharged to ground;
• when the transient fault condition is present at the input terminal or output terminal of the voltage regulator, balancing a current within an active load of a differential amplifier of an error amplifier of the voltage regulator to clamp the output of the differential amplifier to its normal operating point;
• when the transient fault condition ends, setting the output voltage of the error amplifier such that a pass transistor of the regulator responds quickly to resume the regulation;
• sensing of the input voltage level and the output current level for the presence of the transient fault conditions;
• and
• disabling the current balancing when the transient fault conditions are not present.

A control loop circuit for balancing an active load current in a differential amplifier resulting from removal of a transient fault condition applied to an input terminal or output terminal of an external circuit, the control loop circuit comprising:

• a transient fault sense circuit configured for receiving a feedback signal signifying that an input or output transient fault has occurred and configured for generating a transient fault indicator signal indicating an occurrence of the input or output transient fault;
• and
• a local control loop in communication with the transient fault sense circuit and configured for receiving the transient indicator signal;
• wherein the control loop circuit is configured such that when the transient fault indicator signal indicates the input or output transient fault, the local control loop balances the active load current of the differential amplifier and clamps an output of the differential amplifier at a voltage level approaching an operating level of the differential amplifier to force a pass transistor of an external circuit to be maintained in a deep triode region of operation for insuring fast response in controlling the gate of the pass transistor to minimize overshoot when the input terminal or output terminal is returned to its normal operating voltage or current.

A method for balancing an active load of an operational amplifier comprising the steps of:

• monitoring an input voltage at the input terminal or a current at the output terminal of an external circuit to sense if there is a transient fault condition;
• providing a Miller capacitance at the output terminal of an operational amplifier of the external circuit to prevent the output of the operational amplifier from being discharged to ground;
• when the transient fault condition is present at the input terminal or output terminal of the voltage regulator, balancing a current within an active load of a operational amplifier of the voltage regulator to clamp the output of the operational amplifier to its normal operating point;
• when the transient fault condition ends, setting the output voltage of the operational amplifier such that a pass transistor of the regulator responds quickly to resume the regulation and the overshoot is reduced or eliminated;
• sensing of the input voltage level and the output current level for the presence of the transient fault condition;
• and
• disabling the current balancing when the transient fault condition is not present.