| 摘要 |
PROBLEM TO BE SOLVED: To provide a DRAM backup device capable of surely performing backup operation even when a backup power source of DRAM drops, and reducing the cost. SOLUTION: The DRAM backup device of this invention has a 1st power source to be supplied to the DRAM in normal operation; a secondary battery for supplying power to the DRAM instead of the 1st power source when the voltage of the 1st power source drops; a power changeover control circuit for controlling changeover between the 1st power source and the secondary battery to the DRAM; and a DRAM self-refresh control circuit for controlling to shift the DRAM to a self-refresh mode with the power source changeover operation or recover from the self-refresh mode. The power changeover control circuit and the DRAM self-refresh control circuit are backed up by the primary battery when the 1st power source voltage drops. COPYRIGHT: (C)2004,JPO
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