DS1218 Datasheet | Maxim Integrated

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 100n A of battery current PIN ASSIGNMENT VCCO NC NC 1 2 3 4 8 VCCI 7 VBAT 6 CEO 5 CEI PIN DESCRIPTION VCCI - Input +5 Volt Supply VCCO - RAM Power (VCC) Supply - Chip Enable Input NC - No Connection 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. Ining power is monitored for an out-of-tolerance condition. When such a condition is detected, the chip enable output is inhibited to acplish 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 bining 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 is greater. This switch has a voltage drop of less than 0.2V. The second function which the nonvolatile controller provides is power-fail detection. The DS1218 constantly monitors the VCC supply. When VCCI falls to 1.26 times the battery voltage, a precision parator outputs a power-fail detect signal to the chip enable logic. The third function of write protection is acplished by holding the chip enable output signal to within 0.2V of the VCCI or battery supply, when a power-fail condition is detected. During nominal supply conditions, the chip enable...