DS1218

19-6295; Rev 6/12 DS1218 Nonvolatile Controller FEATURES  Converts CMOS RAM into nonvolatile memories  Unconditionally write protects when VCC is out of tolerance  Automatically switches to battery when power fail occurs  Space saving 8-pin PDIP or 8-pin 150 mil SO Packages  Consumes less than 100nA of battery current PIN ASSIGNMENT VCCO NC NC GND 1 2 3 4 8 VCCI 7 VBAT 6 CEO 5 CEI PIN DESCRIPTION VCCI - Input +5 Volt Supply VCCO - RAM Power (VCC) Supply CEI - Chip Enable Input NC - No Connection CEO VBAT GND - Chip Enable Output - + Battery - Ground DESCRIPTION The DS1218 is a CMOS circuit which solves the application problems of converting CMOS RAM into nonvolatile memory. Incoming power is monitored for an out-of-tolerance condition. When such a condition is detected, the chip enable output is inhibited to accomplish write protection and the battery is switched on to supply RAM with uninterrupted power. Special circuitry uses a low-leakage CMOS process which affords precise voltage detection at extremely low battery consumption. The 8-pin package keeps PC board real estate requirements to a minimum. By combining the DS1218 nonvolatile controller chip with a full CMOS memory and lithium batteries, 10 years of nonvolatile RAM operation can be achieved. OPERATION The DS1218 Nonvolatile Controller performs the circuit functions required to battery back-up a RAM. First, a switch is provided to direct power from the battery or VCCI supply, depending on which i...