An integrated circuit has a first pin, a voltage outputting circuit electrically connected to the first pin, a second pin, a current receiving circuit electrically connected to the second pin and a comparing circuit electrically connected to the current receiving circuit. The voltage outputting circuit outputs a first current which flow into the current receiving circuit through the second pin. After receiving the first current, the current receiving circuit outputs an output current to the comparing circuit and the comparing circuit compares the output current and a reference current to output an output signal.