Patent ID: 8847565

Claim:
An apparatus comprising: a first resistor coupled between a voltage supply line subject to voltage fluctuations and a bandgap voltage supply line; a bandgap reference voltage circuit coupled to the bandgap voltage supply line and configured and arranged to provide a bandgap reference voltage output; a second resistor coupled, via the bandgap voltage supply line, to the first resistor and the bandgap reference voltage circuit; a first circuit configured and arranged to shunt current between the bandgap voltage supply line and a ground circuit, the first circuit including a first transistor having a source and drain coupled between the bandgap voltage supply line and the ground circuit, and a gate connected to the bandgap voltage supply line via the second resistor, and a capacitor coupled between the gate and the ground circuit and configured and arranged with the second resistor to maintain the voltage at the gate at an about steady value in response to voltage fluctuations on the bandgap voltage supply line, the first circuit being responsive to the voltage at the gate and an increase in voltage on the bandgap voltage supply line by passing increased current between the voltage supply line and the ground circuit and regulating the voltage supply to the bandgap reference voltage circuit at an about constant level; and a second circuit coupled between the second resistor and the ground circuit, the second circuit being configured and arranged to provide a startup voltage for the bandgap reference voltage circuit by mitigating current flow via the first circuit in response to a voltage level on the bandgap voltage supply line that is less than a minimum voltage at which the bandgap reference circuit can operate.