Dallas Semiconductor DS1213B Datasheet

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DS1213B

SmartSocket 16k/64k

FEATURES

 Accepts standard 2K x 8 or 8K x 8 CMOS

static RAMs

 Embedded lithium energy cell retains RAM

data

 Self-contained circuitry safeguards data  Data retention time is greater than 10 years

with proper RAM selection

 IC socket permits upgrading from 2K x 8 to

8K RAM

 Proven gas-tight socket contacts  Operating temperature range 0°C to 70°C

PIN ASSIGNMENT

9 10 11

12 13

GND 14

28-Pin Intelligent Socket

28 V 27

26 V 25 24 23 22 21 20 CE 19 18

17 16 15

PIN DESCRIPTION

CE - Conditioned Chip Enable

- Switched V

GND - Ground All pins pass through except 20, 26 and 28.

DESCRIPTION

The DS1213B SmartSocket is a 28-pin, 600 mil DIP socket with a built-in CMOS controller circuit and an embedded lithium energy source. It accepts either 24-pin 2K x 8 (lower-justified) or 28-pin 8K x 8 JEDEC bytewide CMOS static RAM. When the socket is mated with a CMOS RAM, it provides a complete solution to problems associated with memory volatility. The Smart-Socket monitors incoming VCC for an out-of-tolerance condition. When such a condition occurs, the internal lithium energy source is automatically switched on and write protection is unconditionally enabled to prevent data corruption.

Using the SmartSocket saves printed circuit board space since the SRAM/SmartSocket combination occupies no more area than the SRAM alone. The SmartSocket modifies only pins 20, 26 and 28, to nonvolatize the RAM. All other pins are passed straight through.

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DS1213B

OPERATION

The DS1213B SmartSocket performs five circuit functions required to battery back up a CMOS memor y. The first function involves switching between the battery and the VCC supply, depending on which is greater. The switch has a voltage drop of less than 0.2 volts.

The second function is power-fail detection. The DS1213B constantly monitors the V V

falls below 4.75 volts, a precision comparator detects the condition and inhibits the RAM chip

supply. When

enable.

The third function, write protection, is accomplished by holding the RAM chip enable signal to within 0.2 volts of VCC or the battery supply whichever is greater. If the incoming chip enable signal is active at the time power fail detection occurs, write protection is delayed until after the current memory cycle is complete to avoid corruption of data. Power fail detection occurs in the range of 4.75 to 4.5 volts. During nominal power supply conditions the chip enable signal will be passed through from the socket pin to the socket contact with a maximum propagation delay of 20 ns.

The fourth function the DS1213B performs is to check battery status to warn of potential dat a loss. Each time that VCC power is restored to the SmartSocket the battery voltage is checked with a precision comparator. If the battery supply is less than 2.0 volts, the second memory access to the SmartSocket is inhibited. Battery status can, therefore, be determined by a three-step process. First, a read cycle is performed to any location in the memory, in order to save the contents of that location. A subsequent write cycle can then be executed to the same memory location, altering the data. If the next read cycle fails to verify the written data, then the battery voltage is less than 2.0V and data is in danger of being corrupted.

The fifth function the SmartSocket provides is battery redundancy. In many applications, data integrity is paramount. In these applications it is desirable to use two batteries to ensure reliability. The DS1213B SmartSocket provides two batteries and an internal isolation switch to select between them. During battery back up, the battery with the highest voltage is selected for use. If one battery fails, the other automatically takes over. The switch between batteries is transparent to the user. A battery status warning will occur if both batteries are less than 2.0 volts. Each of the two internal lithium cells has a 45 mAh capacity.

NOTE:

As shipped from Dallas Semiconductor, battery voltage cannot be measured on the VCC socket contact. Only after V be present on socket contacts 28, 26 and 20.

has been applied to the device for the first time and then removed will the battery voltage

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DS1213B

ABSOLUTE MAXIMUM RATINGS*

Voltage on Any Pin Relative to Ground -0.3V to +7.0V Operating Temperature 0°C to 70°C Storage Temperature -40°C to +70°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

PIN 26 L, PIN 28 L Supply Voltage Logic 1 PIN 20 L V Logic 0 PIN 20 L V

IH IL

4.75 5.0 5.5 V 1,3

2.2 V

+0.3 V 1,3

-0.3 +0.8 V 1,3

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

= 4.75 to 5.5V)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

PIN 26 L, PIN 28 L

5 mA 3,4,5 Supply Current PIN 26 U, PIN 28 U

CCO

VCC -0.2 V 1,3,8 Supply Voltage PIN 26 U, PIN 28 U

CCO

80 mA 3,8

Supply Current PIN 20 L CE Input Leakage PIN 20 U CE Output @ 2.4V PIN 20 U CE Output @ 4V

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

-1.0 +1.0

µA

3,4

-1.0 mA 2,3

4.0 mA 2,3

< 4.5V)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

PIN 20 Output V

PIN 26 U, PIN 28 U

BAT

OHL

BAT-

-0.2

0.2

V 1,3

µA

3,6 Battery Current PIN 26 U, PIN 28 U

BAT

2 3 3.6 V 1,3

Battery Voltage

CAPACITANCE (TA = 25°°°°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Input Capacitance PIN 20 L C Output Capacitance PIN 20 U C

OUT

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