Soft-start switch with voltage regulation and current limiting

A voltage regulator with current limiting for providing pass current to a load, the voltage regulator having an input and an output, the voltage regulator comprising:

• a voltage-controlled current device to control the pass current, with a first terminal, a second terminal, and a third terminal, wherein the second terminal is coupled to the input of the voltage regulator and the third terminal is coupled to the output of the voltage regulator, wherein the pass current flows between the second and third terminals and is responsive to the voltage difference between the first and third terminals;
• a control circuit to control the voltage at the output of the voltage regulator, with an input and with an output coupled to the first terminal of the voltage-controlled current device, wherein the coupling between the control circuit and the output of the voltage regulator is such as to provide negative feedback;
• voltage means, coupled to the output of the control circuit and the third terminal of the voltage-controlled current device, for providing a first voltage at a first node and a second voltage at a second node, where the first voltage is a first function of a source voltage and of the voltage regulator output voltage and the second voltage is a second function of a third voltage at a third node, where the third node is coupled to the output of the control circuit and the third terminal of the voltage-controlled current device;
• and
• a current limit circuit to cause the control circuit to drive the voltage-controlled current device into an OFF state, so as to limit the pass current, when the first voltage at the first node is less than the second voltage at the second node, where the first and second nodes are coupled to the current limit circuit.

A method for limiting pass current supplied to a load by a power source, the method comprising the steps of:

• providing a voltage-controlled current device having a first terminal, a second terminal coupled to the power source, and a third terminal coupled to the load, wherein the pass current flows between the second and third terminals and there is a transconductance relationship between the pass current and the voltage difference between the first and third terminals;
• controlling, in response to the load voltage and an input reference voltage, the voltage-controlled current device by a control circuit so as to regulate the load voltage in accordance with the input reference voltage, the control circuit having an output with an output voltage coupled to the first terminal of the voltage-controlled current device;
• and
• limiting the pass current in the voltage-controlled current device by forcing the voltage-controlled current device into an OFF state upon determining a first voltage at a first node is less than a second voltage at a second node, where the first voltage is a first function of the voltage at the third terminal of the voltage-controlled current device and the second voltage is a second function of the voltage at the first terminal of the voltage-controlled current device.