Dallas Semiconductor DS1218S, DS1218 Datasheet

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DS1218

Nonvolatile Controlle

FEATURES

PIN ASSIGNMENT

 Converts CMOS RAM into nonvolatile

memories

V

CCO

1

V

CCI

8

 Unconditionally write protects when VCC is

out of tolerance

 Automatically switches to battery when

power fail occurs

 Space saving 8-pin mini-DIP/8-pin 150 mil

NC
NC

GND

2
3
4

V

7

BAT

6

CEO

5

CEI

SOIC

 Consumes less than 100 na of battery current

PIN DESCRIPTION

V

CCI

V

CCO

CEI - Chip Enable Input

- Input +5 Volt Supply

- RAM Power (VCC) Supply

NC - No Connection

CEO - Chip Enable Output

V

BAT

- + 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 protect ion 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 mini­DIP 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

supply, depending on which is greater.

CCI

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

supply. When V

CC

falls to

CCI

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

or battery supply, when a power-fail condition is detected.

CCI

During nominal supply conditions, the chip enable output will follow chip enable input with a maximum
propagation delay of 10 ns.

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DS1218

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
Logic 1 V
Logic 0 V
Battery Supply V

CCI

IH
IL

BAT

4.5 5.0 5.5 V 1

2.0 5.5 V 1

-0.3 0.8 V 1

2.5 3.0 3.5 V 1

DC ELECTRICAL CHARACTERISTICS (0°C to 70°C; V

= 5V ± 10%)

CCI

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Active Current I
Battery Current I
RAM Current
(V

CCO1

≥ V

CCI

RAM Current
(V

≥ V

CCO

CCI

-0.3V)

-0.2V)

I

I

Input Leakage I

CEO Output @ 2.4V
CEO Output @ 0.4V

VCC Trip Point V

CCI
BAT
CCO

CCO

IL

I

OH

I

OL

CCTP

-1.0 +1.0 µA

-1.0 mA

25mA3

100 nA 3, 4

80 mA 5

70 mA

4.0 mA

1.26XV

BAT

CAPACITANCE (tA = 25°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Input Capacitance C
Output Capacitance C

IN

OUT

5pF
7pF

AC ELEC TRICAL CHARACTERISTICS (0°C to 70°C; VCC = 5.0V ± 10%)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

CE Propagation Delay

Recovery at Power-up t
VCC Slew Rate t

CE Pulse Width

t

PD

REC

F

t

CE

0.2 2 ms

500 µs

410ns 2

1.5 µs 6, 7

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