DS1312S - Dallas Semiconductor

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FEATURES

 Converts CMOS SRAM into nonvolatile

memory

 Unconditionally write-protects SRAM when

VCC is out of tolerance

 Automatically switches to battery backup

supply when VCC power failure occurs

 Monitors voltage of a lithium cell and

provides advanced warning of impending

battery failure

 Signals low-battery condition on active low

Battery Warning output signal

 Optional -5% or -10% power-fail detection

 Space-saving 8-pin DIP and SOIC packages

 Optional 16-pin SOIC and 20-pin TSSOP

versions reset processor when power failure

occurs and hold processor in reset during

system power-up

 Industrial temperature range of -40°C to

+85°C

PIN ASSIGNMENT

PIN DESCRIPTION

VCCI - +5V Power Supply Input

VCCO - SRAM Power Supply Output

VBAT - Backup Battery Input

CEI - Chip Enable Input

CEO - Chip Enable Output

TOL - VCC Tolerance Select

BW - Battery Warning Output

(Open Drain)

RST - Reset Output (Open Drain)

GND - Ground

NC - No Connection

DESCRIPTION

The DS1312 Nonvolatile Controller with Battery Monitor is a CMOS circuit which solves the application

problem of converting CMOS RAM into nonvolatile memory. Incoming power is monitored for an out-

of-tolerance condition. When such a condition is detected, chip enable is inhibited to accomplish write

protection and the battery is switched on to supply the RAM with uninterrupted power. Special circuitry

uses a low-leakage CMOS process which affords precise voltage detection at extremely low battery

consumption.

DS1312

Nonvolatile Controller with Lithium

Battery Monitor

www.dalsemi.com

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VCCI

RST

CEO

CEI

VCCO

VBAT

TOL

GND

DS1312E 20-Pin TSSOP

GND

TOL

VBAT

VCCO VCCI

CEO

CEI

DS1312S-2 8-Pin SOIC

(150-mil)

GND

TOL

VBAT

VCCO VCCI

CEO

CEI

DS1312 8-Pin DIP

(300-mil)

VCCO

VBAT

TOL

GND

VCCI

RST

CEO

CEI

DS1312S 16-Pin SOIC

(300-mil)

DS1312

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In addition to battery-backup support, the DS1312 performs the important function of monitoring the

remaining capacity of the lithium battery and providing a warning before the battery reaches end-of-life.

Because the open-circuit voltage of a lithium backup battery remains relatively constant over the majority

of its life, accurate battery monitoring requires loaded-battery voltage measurement. The DS1312

performs such measurement by periodically comparing the voltage of the battery as it supports an internal

resistive load with a carefully selected reference voltage. If the battery voltage falls below the reference

voltage under such conditions, the battery will soon reach end-of-life. As a result, the Battery Warning

pin is activated to signal the need for battery replacement.

MEMO RY BACKUP

The DS1312 performs all the circuit functions required to provide battery-backup for an SRAM. First, the

device provides a switch to direct power from the battery or the system power supply (VCCI). Whenever

VCCI is less than the switch point VSW and VCCI is less than the battery voltage VBAT, the battery is

switched in to provide backup power to the SRAM. This switch has voltage drop of less than 0.2 volts.

Second, the DS1312 handles power failure detection and SRAM write-protection. VCCI is constantly

monitored, and when the supply goes out of tolerance, a precision comparator detects power failure and

inhibits chip enable output ( CEO ) in order to write-protect the SRAM. This is accomplished by holding

CEO to within 0.2 volts of VCCO when VCCI is out of tolerance. If CEI is (active) low at the time that

power failure is detected, the CEO signal is kept low until CEI is brought high again. Once CEI is

brought high, CEO is taken high and held high until after VCCI has returned to its nominal voltage level. If

CEI is not brought high by 1.5 µs after power failure is detected, CEO is forced high at that time. This

specific scheme for delaying write protection for up to 1.5 µs guarantees that any memory access in

progress when power failure occurs will complete properly. Power failure detection occurs in the range

of 4.75 to 4.5 volts (5% tolerance) when the TOL pin is wired to GND or in the range of 4.5 to 4.25 volts

(10% tolerance) when TOL is connected to VCCO.

BATTERY VOLTAGE MONITORING

The DS1312 automatically performs periodic battery voltage monitoring at a factory-programmed time

interval of 24 hours. Such monitoring begins within tREC after VCCI rises above VCCTP, and is suspended

when power failure occurs.

After each 24-hour period (tBTCN) has elapsed, the DS1312 connects VBAT to an internal 1.2 MΩ=test

resistor (RINT) for one second (tBTPW). During this one second, if VBAT falls below the factory-

programmed battery voltage trip point (VBTP), the battery warning output BW is asserted. While BW is

active battery testing will be performed with period tBTCW to detect battery removal and replacement.

Once asserted, BW remains active until the battery is physically removed and replaced by a fresh cell.

The battery is still retested after each VCC power-up, however, even if BW was active on power-down. If

the battery is found to be higher than VBTP during such testing, BW is deasserted and regular 24-hour

testing resumes. BW has an open-drain output driver.

Battery replacement following BW activation is normally done with VCCI nominal so that SRAM data is

not lost. During battery replacement, the minimum time duration between old battery detachment and

new battery attachment (tBDBA) must be met or BW will not deactivate following attachment of the new

battery. Should BW not deactivate for this reason, the new battery can be detached for tBDBA and then re-

attached to clear BW .

DS1312

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NOTE: The DS1312 cannot constantly monitor an attached battery because such monitoring would

drastically reduce the life of the battery. As a result, the DS1312 only tests the battery for one second out

of every 24 hours and does not monitor the battery in any way between tests. If a good battery (one that

has not been previously flagged with BW ) is removed between battery tests, the DS1312 may not

immediately sense the removal and may not activate BW until the next scheduled battery test. If a battery

is then reattached to the DS1312, the battery may not be tested until the next scheduled test.

NOTE: Battery monitoring is only a useful technique when testing can be done regularly over the entire

life of a lithium battery. Because the DS1312 only performs battery monitoring when VCC is nominal,

systems which are powered-down for excessively long periods can completely drain their lithium cells

without receiving any advanced warning. To prevent such an occurrence, systems using the DS1312

battery monitoring feature should be powered–up periodically (at least once every few months) in order

to perform battery testing. Furthermore, anytime BW is activated on the first battery test after a power-up,

data integrity should be checked via checksum or other technique.

POWER MONITORING

DS1312S and DS1312E varieties have an additional reset pin. These varieties detect out-of-tolerance

power supply conditions and warn a processor-based system of impending power failure. When VCCI falls

below the trip point level defined by the TOL pin (VCCTP), the VCCI comparator activates the reset signal

RST . Reset occurs in the range of 4.75 to 4.5 volts (5% tolerance) when the TOL pin is connected to

GND or in the range of 4.5 to 4.25 volts (10% tolerance) when TOL is connected to VCCO.

RST also serves as a power-on reset during power-up. After VCCI exceeds VCCTP, RST will be held active

for 200 ms nominal (tRPU). This reset period is sufficiently long to prevent system operation during

power-on transients and to allow tREC to expire. RST has an open-drain output driver.

FRESHNESS SEAL MODE

When the battery is first attached to the DS1312 without VCC power applied, the device does not

immediately provide battery-backup power on VCCO. Only after VCCI exceeds VCCTP and later falls below

both VSW and VBAT will the DS1312 leave Freshness Seal Mode and provide battery-backup power. This

mode allows a battery to be attached during manufacturing but not used until after the system has been

activated for the first time. As a result, no battery energy is drained during storage and shipping.

DS1312

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FUNCTIONAL BLOCK DIAGRAM Figure 1

DS1312

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ABSOLUTE MAXIMUM RA TINGS*

Voltage on Any Pin Relative to Ground -0.5V to +7.0V

Operating Temperature -40°C to +85°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 (-40°C to +85°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Supply Voltage TOL=GND VCCI 4.75 5.0 5.5 V 1

Supply Voltage TOL=VCCO VCCI 4.5 5.0 5.5 V 1

Battery Supply Voltage VBAT 2.0 6.0 V 1

Logic 1 Input VIH 2.0 VCCI+0.3 V 1, 12

Logic 0 Input VIL -0.3 +0.8 V 1, 12

DC ELECTRICAL CHARACTERISTI CS (-40°C to +85°C; VCCI >VCCTP)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Operating Current (TTL inputs) ICC1 200 400 µA 2

Operating Current (CMOS inputs) ICC2 50 100 µA 2, 5

RAM Supply Current

(VCCO ≥ VCCI -0.2V)

ICCO1 140 mA 3

RAM Supply Current

(VCCO ≥ VCCI -0.3V)

ICCO1 200 mA 4

VCC Trip Point (TOL=GND) VCCTP 4.50 4.62 4.75 V 1

VCC Trip Point (TOL=VCCO)V

CCTP 4.25 4.37 4.50 V 1

VBAT Trip Point VBTP 2.5 2.6 2.7 V 1

VCC/VBAT Switch Point VSW 2.6 2.7 2.8 V 1

Output Current @ 2.4V IOH -1 mA 7, 10

Output Current @ 0.4V IOL 4 mA 7, 10

Input Leakage IIL -1.0 +1.0 µA

Output Leakage ILO -1.0 +1.0 µA

Battery Monitoring Test Load RINT 0.8 1.2 1.5 MΩ

DC ELECTRICAL CHARACTERISTI CS (-40°C to +85°C; VCCI < VBAT; VCCI < VSW)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Battery Current IBAT 100 nA 2

Battery Backup Current ICCO2 500 µA 6

Supply Voltage VCCO VBAT-0.2 V1

CEO Output VOHL VBAT-0.2 V 1, 8

DS1312

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CAPACITANCE (tA =25°C)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Input Capacitance ( CEI , TOL) CIN 7pF

Output Capacitance

(CEO ,BW ,RST )

COUT 7pF

AC EL ECTRICAL CHARACTERISTICS (-40°C to +85°C; VCCI > VCCTP)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

CEI to CEO Propagation Delay tPD 510ns

CE Pulse Width tCE 1.5 µs 11

VCC Valid to End of

Write Protection

tREC 12 125 ms 9

VCC Valid to CEI Inactive tPU 2ms

VCC Valid to RST Inactive tRPU 150 200 350 ms 10

VCC Valid to BW Valid tBPU 1s10

AC EL ECTRICAL CHARACTERISTICS (-40°C to +85°C; VCCI < VCCTP)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

VCC Slew Rate tF150 µs

VCC Fail Detect to RST Active tRPD 515µs10

VCC Slew Rate tR150 µs

AC EL ECTRICAL CHARACTERISTICS (-40°C to +85°C; VCCI > VCCTP)

PARAMETER SYMBOL MIN TYP MAX UNITS NOTES

Battery Test to BW Active tBW 1s10

Battery Test Cycle-Normal tBTCN 24 hr

Battery Test Cycle-Warning tBTCW 5s

Battery Test Pulse Width tBTPW 1s

Battery Detach to Battery Attach tBDBA 7s

Battery Attach to BW Inactive tBABW 1s10

DS1312

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TIMING DI AGRAM: POWER-UP

NOTE:

If VBAT < VSW, VCCO will begin to slew with VCCI when VCCI = VBAT.

DS1312

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TIMING DI AGRAM: POWER-DOWN

NOTE:

If VBAT < VSW, VCCO will slew down with VCCI until VCCI = VBAT.

DS1312

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TIMING DI AGRAM: BATTERY WARNING DETECTION

NOTE:

tBW is measured from the expiration of the internal timer to the activation of the battery warning output

BW .

TIMING DIAGRAM: BATTERY REPLACEMENT

DS1312

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NOTES:

1. All voltages referenced to ground.

2. Measured with outputs open circuited.

3. ICCO1 is the maximum average load which the DS1312 can supply to attached memories at VCCO >

VCCI -0.2V.

4. ICCO1 is the maximum average load which the DS1312 can supply to attached memories at VCCO >

VCCI -0.3V.

5. All inputs within 0.3V of ground or VCCI.

6. ICCO2 is the maximum average load current which the DS1312 can supply to the memories in the

battery backup mode.

7. Measured with a load as shown in Figure 2.

8. Chip Enable Output CEO can only sustain leakage current in the battery backup mode.

9. CEO will be held high for a time equal to tREC after VCCI crosses VCCTP on power-up.

10. BW and RST are open-drain outputs and, as such, cannot source current. External pull-up resistors

should be connected to these pins for proper operation. Both BW and RST can sink 10 mA.

11. tCE maximum must be met to ensure data integrity on power-down.

12. In battery-backup mode, inputs must never be below ground or above VCCO.

13. The DS1312 is recognized by Underwriters Laboratory (U.L.®) under file E99151.

DC TEST CONDITIONS

Outputs Open

All voltages are referenced to ground

AC TEST CONDITIONS

Output Load: See below

Input Pulse Levels: 0 - 3.0V

Timing Measurement Reference Levels

Input: 1.5V

Output: 1.5V

Input pulse Rise and Fall Times: 5 ns

OUTPUT LOAD Figure 2

DS1312

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DATA SHEET REVISION SUMMARY

The following represent the key differences between 12/16/96 and 06/12/97 version of the DS1312 data

sheet. Please review this summary carefully.

1. Changed VBAT max to 6V

2. Changed tBABW from 75 to 1s max

3. Changed block diagram to show UL compliance

The following represent the key differences between 06/12/97 and 08/29/97 version of the DS1312 data

sheet. Please review this summary carefully.

1. Changed AC test conditions

The following represent the key differences between 08/29/97 and 12/16/97 version of the DS1312 data

sheet. Please review this summary carefully.

1. Specified Input Capacitance as being only for CEI , TOL and output capacitance as being only for

CEO , BW and RST . This is not a change but rather a clarification.

2. Add note 13 describing UL recognition.