An apparatus includes a first terminal, a second terminal, a bi-directional regulator circuit, and functional circuitry. The bi-directional regulator circuit generates a voltage across a first power supply node and a second power supply node in response to an input current flowing through the first terminal and the second terminal with a first polarity. The bi-directional regulator circuit also generates the voltage across the first power supply node and the second power supply node in response to the input current flowing through the first terminal and the second terminal with a second polarity opposite the first polarity. The functional circuitry is powered by the voltage and is configured to generate a signal using the voltage. The signal is indicative of the input current in response to the input current being supplied to the first terminal and is indicative of the input current in response to presence of the input current.