DS1218 DALLAS | Alldatasheet

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Technical content

FEATURES

/elevenoclock Converts CMOS RAM into nonvolatile memories /elevenoclock Unconditionally write protects when VCC is out of tolerance /elevenoclock Automatically switches to battery when power fail occurs /elevenoclock Space saving 8-pin mini-DIP/8-pin 150 mil SOIC /elevenoclock Consumes less than 100 na of battery current PIN ASSIGNMENT PIN DESCRIPTION VCCI - Input +5 Volt Supply VCCO - RAM Power (VCC) Supply CEI - Chip Enable Input NC - No Connection CEO - Chip Enable Output VBAT - + Battery GND - 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 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. 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 V CCI 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 V CC supply. When V CCI 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 to within 0.2V of the V CCI 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 propagation delay of 10 ns. DS1218 Nonvolatile Controller www.dalsemi.com VCCO NC NC GND VCCI VBAT CEO CEI

ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground -0.5V to +7.0V Operating Temperature 0 °C to 70°C Storage Temperature -55 °C to +125°C Soldering Temperature 260 °C for 10 seconds * This 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) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Supply V CCI 4.5 5.0 5.5 V 1 Logic 1 V IH 2.0 5.5 V 1 Logic 0 V IL -0.3 0.8 V 1 Battery Supply V BAT 2.5 3.0 3.5 V 1 DC ELECTRICAL CHARACTERISTICS (0°C to 70°C; VCCI = 5V ± 10%) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Active Current I CCI 25 m A 3 Battery Current I BAT 100 nA 3, 4 RAM Current (VCCO1 ≥ VCCI -0.3V) ICCO 80 mA 5 RAM Current (VCCO ≥ VCCI -0.2V) ICCO 70 mA Input Leakage I IL -1.0 +1.0 µA CEO Output @ 2.4V IOH -1.0 mA CEO Output @ 0.4V IOL 4.0 mA VCC Trip Point V CCTP 1.26XVBAT CAPACITANCE (tA = 25°C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Input Capacitance C IN 5p F Output Capacitance C OUT 7p F AC ELECTRICAL CHARACTERISTICS (0°C to 70°C; VCC = 5.0V ± 10%) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES CE Propagation Delay tPD 41 0n s 2 Recovery at Power-up t REC 0.2 2 ms VCC Slew Rate t F 500 µs CE Pulse Width tCE 1.5 µs 6, 7

TIMING DIAGRAM: POWER-UP TIMING DIAGRAM: POWER-DOWN

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