A rush-in current controller includes a clock module connected to provide a delayed sleep control signal based on counting a preset number of clock cycles corresponding to an input sleep control signal. Additionally, the rush-in current controller includes a ring oscillator module connected to maintain the delayed sleep control signal based on counting a preset number of ring oscillator cycles corresponding to a virtual power supply line voltage. A method of controlling a rush-in current includes providing a delayed sleep control signal based on counting a preset number of clock cycles corresponding to an input sleep control signal and maintaining the delayed sleep control signal based on counting a preset number of ring oscillator cycles corresponding to a virtual power supply line voltage.