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DS1218
Nonvolatile Controller
FEATURESConverts CMOS RAM into nonvolatile
memoriesUnconditionally write protects when VCC isout of toleranceAutomatically switches to battery when
power fail occursSpace saving 8-pin mini-DIP/8-pin 150 mil
SOICConsumes less than 100 na of battery current
PIN ASSIGNMENT
PIN DESCRIPTIONVCCI- Input +5 Volt Supply
VCCO- RAM Power (VCC) Supply
CEI- Chip Enable Input- No Connection
CEO- Chip Enable Output
VBAT- + Battery
GND- Ground
DESCRIPTIONThe 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 mini-DIP 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.
OPERATIONThe 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 comparator outputs a power-fail detect signal to the chip enable
logic. The third function of write protection is accomplished by holding the chip enable output signal towithin 0.2V of the VCCI or battery supply, when a power-fail condition is detected.
During nominal supply conditions, the chip enable output will follow chip enable input with a maximum
DS1218VCCO
GND
VCCI
VBAT
CEO
CEI
DS1218
ABSOLUTE MAXIMUM RATINGS*Voltage on Any Pin Relative to Ground-0.5V to +7.0V
Operating Temperature0°C to 70°C
Storage Temperature-55°C to +125°C
Soldering Temperature260°C for 10 secondsThis is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS(0°C to 70°C)
DC ELECTRICAL CHARACTERISTICS(0°C to 70°C; VCCI = 5V ± 10%)
CAPACITANCE(tA = 25°C)
AC ELECTRICAL CHARACTERISTICS(0°C to 70°C; VCC = 5.0V ± 10%)
DS1218
TIMING DIAGRAM: POWER-UP
TIMING DIAGRAM: POWER-DOWN
DS1218
NOTES:1. All voltages referenced to ground.
2. Measured with a load as shown in Figure 1.
3. Outputs open.
4. Drain from battery when VCC < VBAT.
5. Maximum amount of current which can be drawn through pin 1 of the controller.
6. tCE max must be met to ensure data integrity on power loss.
7. CEO can only sustain leakage current in the battery backup mode.
OUTPUT LOAD Figure 1
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