These ICs were developed for STATIC-RAM (S-RAM) battery back-up, and have built-in switching circuit for main power supply and battery, back-up timing circuit and battery checker. Power ON/OFF and momentary power interruptions can damage S-RAM data on equipment that contains an S-RAM. These ICs switch the S-RAM to back-up mode (CS signal makes S-RAM CE pin low and CE pin high) when power supply voltage goes below a set voltage (detection voltage 4.2V typ., variable), preventing damage to data. Further, when power supply voltage drops, these ICs switch from main power supply to battery back-up (switching voltage 3.3V typ.). Then, when power supply voltage rises, they first switch the SRAM from battery back-up state to main power supply (switching voltage 3.3V typ.), and from back-up mode to normal mode (CS signal makes S-RAM CE pin high and CE pin low). These signal processes provide reliable protection against data damage. The CS signal also can absorb power supply chattering and roughness through the external capacitor. There is a built-in battery checker to monitor the back-up battery voltage, and this circuit is turned ON/OFF by the control pin.