Memory device and memory system for performing target refresh operation, and operation method thereof

A memory system, comprising:

• a memory controller configured to periodically apply a normal refresh command at the refresh interval, and non-periodically apply a refresh management command;
• and
• a memory device configured to:
• generate an internal target refresh command whenever a number of inputs of the normal refresh command reaches a target number, and
• adjust the target number by comparing a refresh counting value generated based on a number of inputs of the refresh management command and a number of issuances of the internal target refresh command, with a target value corresponding to temperature information.

An operation method of a memory device, the operation method comprising:

• receiving a normal refresh command or a refresh management command from a memory controller;
• generating an internal target refresh command whenever a number of inputs of the normal refresh command reaches a target number;
• calculating a refresh counting value by summing a number of inputs of the refresh management command and a number of issuances of the internal target refresh command;
• generating a rate control signal by comparing the refresh counting value with a target value corresponding to temperature information;
• and
• adjusting the target number according to the rate control signal.

An operating method of a memory device, comprising:

• performing first and second refresh operations, which are independent from each other;
• performing a third refresh operation when the first refresh operation is performed a reference number of times;
• and
• adjusting the reference number based on comparison between a sum and a threshold,
• wherein the sum is a number of times that the respective second and third refresh operations are performed, and
• wherein the threshold depends on a temperature of the memory device.