Apparatus and methods for amplifier fault protection

An apparatus comprising:

• an amplifier including an output configured to generate an output signal;
• a signal pin configured to receive the output signal from the output of the amplifier;
• a fault protection circuit electrically connected between the output of the amplifier and the signal pin, wherein the fault protection circuit comprises a first transistor and a second transistor, wherein the first transistor includes a drain electrically connected to the output of the amplifier, a source, and a gate, and wherein the second transistor includes a drain electrically connected to the signal pin, a source electrically connected to the source of the first transistor, and a gate;
• and
• a fault protection control circuit configured to control the fault protection circuit at least in part by controlling voltage levels of the gates of the first and second transistors, wherein the fault protection control circuit includes an overvoltage detection and control circuit configured to detect an overvoltage condition of the signal pin and to turn off the first transistor when the overvoltage condition is detected and otherwise turn on the first transistor, and wherein the fault protection circuit further includes an undervoltage detection and control circuit configured to detect an undervoltage condition of the signal pin and to turn off the second transistor when the undervoltage condition is detected and otherwise turn on the second transistor,
• wherein, the fault protection control circuit is powered at least in part by the signal pin, and wherein a bias of the fault protection control circuit is provided by the signal pin by current at a node of the sources of the first and second transistors,
• wherein the overvoltage detection and control circuit comprises a first high voltage current source and a first resistor, wherein the first resistor is electrically connected between the gate and the source of the first transistor, and wherein the first high voltage current source is configured to provide a first current through the first resistor when no overvoltage condition is detected so as to keep on the first transistor.

An apparatus comprising:

• an amplifier including an output configured to generate an output signal;
• a signal pin configured to receive the output signal from the output of the amplifier;
• a fault protection circuit electrically connected between the output of the amplifier and the signal pin, wherein the fault protection circuit comprises a first transistor and a second transistor, wherein the first transistor includes a drain electrically connected to the output of the amplifier, a source, and a gate, and wherein the second transistor includes a drain electrically connected to the signal pin, a source electrically connected to the source of the first transistor, and a gate;
• and
• a fault protection control circuit configured to control the fault protection circuit at least in part by controlling voltage levels of the gates of the first and second transistors, wherein the fault protection control circuit is further configured to detect an overvoltage condition of the signal pin and to turn off one of the first transistor or the second transistor when the overvoltage condition is detected, and wherein the fault protection control circuit is further configured to detect an undervoltage condition of the signal pin and to turn off the other of the first transistor or the second transistor when the undervoltage condition is detected,
• wherein the fault protection control circuit is powered at least in part by the signal pin, wherein the fault protection control circuit is configured to turn on the other of the first transistor or the second transistor when the overvoltage condition is detected, and wherein the fault protection control circuit is configured to turn on the one of the first transistor or the second transistor when the undervoltage condition is detected.