GENERAL DESCRIPTION
The SA56600-42 is designed to protect SRAM data in computer systems during periods of sagging power supply voltages and power outages. When the power supply voltage drops to typically 4.2 V, the CS output goes to a logic LOW state pulling CE to a LOW state, disabling the SRAM device. In addition, a reset logic LOW is asserted for system use. If the supply voltage drops further, to 3.3 V typically or lower, the SA56600-42 switches the system’s operation from the main power supply source to the Lithium back-up battery. As the main supply is restored and the voltage rises to 3.3 V or higher, the SRAM support voltage transfers from the Lithium back-up battery to the main supply. When the main supply voltage rises to greater than typically 4.2 V, the CS output goes to a logic HIGH state for SRAM CE control. Reset assertion is released and normal operation is resumed. This sequence ensures reliable preservation of SRAM data during periods of supply deficiency and interruptions.

FEATURES
• Supply switching at 4.2 VDC threshold (falling supply)
• RESET output
• Both CS and CS outputs available for SRAM control
• During battery back-up operation:
    – Low supply current (0.3 µA typical)
    – Low input/output voltage drop (0.3 V typical at 100 µA)
    – Low reverse current leakage (0.1 µA max.)
• During normal operation:
    – Low input/output voltage drop (0.2 V typical at 50 mA)
    – 4.8 V typical output voltage at 50 mA with VCC = 5.0 V
    – Restoration of main supply operation at 3.3 V

APPLICATIONS
• Memory cards (SRAM)
• PCs, word processors
• FAX machines, photocopiers, office equipment
• Sequence controllers
• Video games and other equipment with SRAM