Storage device updating operation voltages based on a number of off cells and method of operating the same

A storage device comprising:

• a memory device comprising a plurality of memory blocks;
• and
• a memory controller configured to control an erase operation, a program operation, and a read operation on the memory device,
• wherein the memory controller is configured to:
• apply a first erase voltage to memory cells included in a first memory block in response to a first erase command for the first memory block;
• determine a number of off-cells, each having a threshold voltage greater than or equal to a reference voltage, among the memory cells;
• obtain a second erase voltage by adding a unit erase voltage to the first erase voltage in response to the number of the off-cells exceeding a reference number;
• and
• apply the second erase voltage to the memory cells in response to a second erase command for the first memory block.

A method of operating a storage device, the method comprising:

• applying a first erase voltage to memory cells included in a first memory block among a plurality of memory blocks in response to a first erase command for the first memory block;
• applying a first program voltage through a first wordline connected to a first page to memory cells included in the first page in the first memory block in response to a first program command for the first page;
• determining a number of off-cells, each having a threshold voltage greater than or equal to a reference voltage, among the memory cells included in the first memory block;
• obtaining a second program voltage by subtracting a unit program voltage from the first program voltage in response to the number of the off-cells exceeding a reference number;
• and
• applying the second program voltage through the first wordline in response to a second program command for the memory cells included in the first page.