Patent ID: 7596048

Claim:
A memory system receiving a power supply from a host device comprising: a non-volatile semiconductor memory; and a controller for controlling writing and reading data to and from the semiconductor memory, in response to a request from the host device, wherein the controller operates in such a manner that an amount of each of n currents is deducted from an amount of a current supplied from the power supply, the n currents having n values that gradually increase from the first to n-th (n is a natural number equal to or larger than 2); when an amount of each of the n currents is deducted from an amount of a current supplied from the power supply in order from the first to n-th values, the controller determines whether or not the corresponding voltage of the power supply falls below a preset detection voltage; and after detecting that a current having the p-th (p is a natural number between 2 and n, inclusive) one of the n values makes the corresponding voltage of the power supply to fall below the detection voltage, the controller operates so that the memory system consumes a current having a value smaller than the p-th one of the n values.