PST518

MITSUMI Battery Backup IC Battery Backup IC 1. Background of Development Around 1985 when began the sales of IC for microcomputer peripheral equipment and system reset IC, a set manufacture inquired of us about IC for control of memory. It was a good change for us to decide a joint development of general purpose IC. This resulted in the development of PST531 and PST532. In 1989 they were improved into the backup IC series dedicated to cards, games (popular-priced) and to 1-chip microcomputers. Our IC series now includes low current consumption type products. 2. What is Battery Backup IC? Such IC memories as S-RAM and D-RAM all volatilize when power supply is cut off. Usually we use batteries not to let these data disappear and to store them for a longer time (of the order of several years). The battery backup IC can monitor main supply when storing data by means of battery and the like, control memory so that there should not arise any data trouble in the memory, change the main supply over to battery, and monitor the residual voltage of the battery, to take a few examples. 3. Basic Configuration Fig. 1 below illustrates the basic configuration of the backup IC. We have PST531, PST532 and MM1026 as IC of the basic configuration. 3-1 Battery/Main Supply Changeover Circuit 1. 3.3V detect circuit ··· Main supply detection 2. Transistor switch ····· Main supply ON/OFF switch 3. Schottky diode ········ For supplying backup power 3-2 Configuration of CS (CE) Control circuit 1. 4...