DS1374C-33+ - Maxim Integrated Products, Inc.

General Description

The DS1374 is a 32-bit binary counter designed to contin-

uously count time in seconds. An additional counter gen-

erates a periodic alarm or serves as a watchdog timer. If

disabled, this counter can be used as 3 bytes of non-

volatile (NV) RAM. Separate output pins are provided for

an interrupt and a square wave at one of four selectable

frequencies. A precision temperature-compensated refer-

ence and comparator circuit monitor the status of VCC to

detect power failures, provide a reset output, and auto-

matically switch to the backup supply when necessary.

Additionally, the reset pin is monitored as a pushbutton

input for externally generating a reset. The device is pro-

grammed serially through an I2C serial interface.

Applications

Portable Instruments

Point-of-Sale Equipment

Medical Equipment

Telecommunications

Features

♦32-Bit Binary Counter

♦Second Binary Counter Provides Time-of-Day

Alarm, Watchdog Timer, or NV RAM

♦Separate Square-Wave and Interrupt Output Pins

♦I2C Serial Interface

♦Automatic Power-Fail Detect and Switch Circuitry

♦Single-Pin Pushbutton Reset Input/Open-Drain

Reset Output

♦Low-Voltage Operation

♦Trickle-Charge Capability

♦-40°C to +85°C Operating Temperature Range

♦10-Pin μSOP, 16-Pin SO

♦Available in a Surface-Mount Package with an

Integrated Crystal (DS1374C)

♦Underwriters Laboratory (UL) Recognized

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

______________________________________________

Maxim Integrated Products

Ordering Information

DS1374

X1 X2

CRYSTAL

VCC

SQW

SCL

SDA

INT

RST

INT

RST GND

VBACKUP

VCC

N.O.

PUSHBUTTON

RESET

PRIMARY

BATTERY,

RECHARGEABLE

BATTERY, OR

SUPER CAPACITOR

CPU

RPU

RPU = tr/CB

RPU

Typical Operating Circuit

Rev 3; 1/06

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE VOLTAGE (V) PIN-PACKAGE TOP MARK**

DS1374C-18 -40°C to +85°C 1.8 16 SO (300 mils) DS1374C-18

DS1374C-18# -40°C to +85°C 1.8 16 SO (300 mils) DS1374C-18

DS1374C-3 -40°C to +85°C 3.0 16 SO (300 mils) DS1374C-3

DS1374C-3# -40°C to +85°C 3.0 16 SO (300 mils) DS1374C-3

DS1374C-33 -40°C to +85°C 3.3 16 SO (300 mils) DS1374C-33

DS1374C-33# -40°C to +85°C 3.3 16 SO (300 mils) DS1374C-33

DS1374C-33/T&R -40°C to +85°C 3.3 16 SO (300 mils)/Tape and Reel DS1374C-33

PI2C,

aI2C-

p I2Cs

t I2Cs.

Pin Configurations appear at the end of the data sheet.

Denotes a RoHS-compliant device that may include lead that is exempt under RoHS requirements. The lead finish is JESD97 category

e3, and is compatible with both lead-based and lead-free soldering processes.

A "#" anywhere on the top mark denotes a RoHS-compliant package.

Ordering Information continued at end of data sheet.

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

2 _____________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

RECOMMENDED DC OPERATING CONDITIONS

(VCC = VCC(MIN) to VCC(MAX), TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

Voltage Range on VCC Pin Relative to Ground .....-0.3V to +6.0V

Voltage Range on SDA, SCL, and WDS

Relative to Ground....................................-0.3V to VCC + 0.3V

Operating Temperature Range ...........................-40°C to +85°C

Storage Temperature Range .............................-55°C to +125°C

Soldering Temperature Range ........................See the

Handling,

PC Board Layout, and Assembly

section.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

DS1374-33 2.97 3.3 5.50

DS1374-3 2.7 3.0 3.3

Supply Voltage

(Notes 2, 3) VCC

DS1374-18 1.71 1.8 1.89

Input Logic 1 VIH (Note 2) 0.7 x VCC VCC + 0.3 V

Input Logic 0 VIL (Note 2) -0.3 +0.3 x

VCC V

Pullup Resistor Voltage (INT,

SQW, SDA, SCL), VCC = 0V VPU (Note 2) 5.5 V

DS1374-33 2.70 2.88 2.97

DS1374-3 2.45 2.6 2.7

Power-Fail Voltage

(Note 2) VPF

DS1374-18 1.51 1.6 1.71

DS1374-33 1.3 3.0 VCC

(MAX

)

Backup Supply Voltage

(Notes 2, 3, 4) VBACKUP

DS1374-3, DS1374-18 1.3 3.0 3.7

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

_____________________________________________________________________ 3

DC ELECTRICAL CHARACTERISTICS

(VCC = VCC(MIN) to VCC(MAX) , TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

R1 (Note 5) 250

R2 (Note 6) 2000

Trickle-Charge Current-Limiting

Resistors R3 (Note 7) 4000

Input Leakage ILI (Note 8) -1 +1

I/O Leakage ILO (Note 9) -1 +1

RST Pin I/O Leakage ILORST (Note 10) -200 +1

µA

SDA Logic 0 Output (VOL = 0.4V) IOLSDA 3.0 mA

VCC > 2V; VOL = 0.4V 3.0

1.71V < VCC < 2V; VOL = 0.2 VCC 3.0 mA

RST, SQW, and INT Logic 0

Outputs (Note 11) IOL1

1.3V < VCC < 1.71V; VOL = 0.2 VCC 250 µA

DS1374-18 75 150

DS1374-3 110 200

Active Supply Current

(Notes 11, 12) ICCA

DS1374-33 180 300

µA

DS1374-18 60 100

DS1374-3 80 125

Standby Current (Notes 11, 13) ICCS

DS1374-33 115 175

µA

VBACKUP Leakage Current

(VBACKUP = 3.7V) IBACKUPLKG 100 nA

DC ELECTRICAL CHARACTERISTICS

(VCC = 0V, VBACKUP = 3.7V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MAX TYP MAX UNITS

VBACKUP Current (OSC ON);

SQW OFF IBKOSC1 (Note 14) 400 700 nA

VBACKUP Current (OSC ON);

SQW ON (32kHz) IBKOSC2 (Notes 14, 15) 600 1000 nA

VBACKUP Data-Retention Current

(OSC OFF) IBACKUPDR 25 100 nA

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

4 _____________________________________________________________________

AC ELECTRICAL CHARACTERISTICS

(VCC = VCC(MIN) to VCC(MAX), TA= -40°C to +85°C, unless otherwise noted.) (Note 1) (Figure 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Fast mode 100 400

SCL Clock Frequency (Note 16) fSCL Standard mode 0 100 kHz

Fast mode 1.3

Bus Free Time Between STOP

and START Conditions tBUF Standard mode 4.7 µs

Fast mode 0.6

Hold Time (Repeated) START

Condition (Note 17) tHD:STA Standard mode 4.0 µs

Fast mode 1.3

Low Period of SCL Clock tLOW Standard mode 4.7 µs

Fast mode 0.6

High Period of SCL Clock tHIGH Standard mode 4.0 µs

Fast mode 0 0.9

Data Hold Time (Notes 18, 19) tHD:DAT Standard mode 0 0.9 µs

Fast mode 100

Data Setup Time (Note 20) tSU:DAT Standard mode 250 ns

Fast mode 0.6

Start Setup Time tSU:STA Standard mode 4.7 µs

Fast mode 300

Rise Time of Both SDA and SCL

Signals (Note 16) tRStandard mode

20 +

0.1CB1000 ns

Fast mode 300

Fall Time of Both SDA and SCL

Signals (Note 16) tFStandard mode

20 +

0.1CB300 ns

Fast mode 0.6

Setup Time for STOP Condition tSU:STO Standard mode 4.7 µs

C ap aci ti ve Load for E ach Bus Li ne CB(Note 16) 400 pF

I/O C ap aci tance ( S D A, S C L) CI/O (Note 21) 10 pF

Pulse Width of Spikes That Must

be Suppressed by the Input Filter tSP Fast mode 30 ns

Pushbutton Debounce PBDB (Figure 2) 250 ms

Reset Active Time tRST (Figure 2) 250 ms

Oscillator Stop Flag (OSF) Delay tOSF (Note 22) 100 ms

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

_____________________________________________________________________ 5

POWER-UP/POWER-DOWN CHARACTERISTICS

(TA= -40°C to +85°C) (Figure 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VCC Detect to Recognize Inputs

(VCC Rising) tRPU (Note 23) 250 ms

VCC Fall Time; VPF(MAX) to

VPF(MIN) tF300 µs

VCC Rise Time; VPF(MIN) to

VPF(MAX) tR0µs

WARNING: Under no circumstances are negative undershoots, of any amplitude, allowed when the device is in write protection.

Note 1: Limits at -40°C are guaranteed by design and not production tested.

Note 2: All voltages are referenced to ground.

Note 3: VBACKUP should not exceed VCC MAX or 3.7V, whichever is greater.

Note 4: The use of the 250Ωtrickle-charge resistor is not allowed at VCC > 3.63V and should not be enabled.

Note 5: Measured at VCC = typ, VBACKUP = 0V, register 09h = A5h.

Note 6: Measured at VCC = typ, VBACKUP = 0V, register 09h = A6h.

Note 7: Measured at VCC = typ, VBACKUP = 0V, register 09h = A7h.

Note 8: SCL only.

Note 9: SDA and SQW and INT.

Note 10: The RST pin has an internal 50kΩpullup resistor to VCC.

Note 11: Trickle charger disabled.

Note 12: ICCA—SCL clocking at max frequency = 400kHz.

Note 13: Specified with I2C bus inactive.

Note 14: Measured with a 32.768kHz crystal attached to the X1 and X2 pins.

Note 15: WDSTR = 1. BBSQW = 1 is required for operation when VCC is below the power-fail trip point (or absent).

Note 16: CB—total capacitance of one bus line in pF.

Note 17: After this period, the first clock pulse is generated.

Note 18: The maximum tHD:DAT only has to be met if the device does not stretch the low period (tLOW) of the SCL signal.

Note 19: A device must internally provide a hold time of at least 300ns for the SDA signal (referred to as the VIHMIN of the SCL sig-

nal) to bridge the undefined region of the falling edge of SCL.

Note 20: A fast-mode device can be used in a standard-mode system, but the requirement tSU:DAT ≥to 250ns must be met. This is

automatically the case if the device does not stretch the low period of the SCL signal. If such a device does stretch the low

period of the SCL signal, it must output the next data bit to the SDA line tRmax + tSU:DAT = 1000 + 250 = 1250ns before

the SCL line is released.

Note 21: Guaranteed by design. Not production tested.

Note 22: The parameter tOSF is the period of time the oscillator must be stopped for the OSF flag to be set over the voltage range of

0V ≤VCC ≤VCC MAX and 1.3V ≤VBACKUP ≤3.7V.

Note 23: This delay applies only if the oscillator is enabled and running. If the EOSC bit is 1, the startup time of the oscillator is

added to this delay.

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

6 _____________________________________________________________________

OUTPUTS

VCC

VPF(MAX)

INPUTS

HIGH-Z

RST

DON'T CARE

VALID

RECOGNIZED RECOGNIZED

VALID

VPF(MIN)

tRST

tRPU

VPF VPF

Figure 3. Power-Up/Power-Down Timing

tRST

PBDB

RST

Figure 2. Pushbutton Reset Timing

SDA

SCL

tHD:STA

tLOW

tHIGH

tRtF

tBUF

tHD:DAT

tSU:DAT REPEATED

START

tSU:STA

tHD:STA

tSU:STO

tSP

STOP START

Figure 1. Data Transfer on I2C Serial Bus

IBAT0SC1 vs. VBAT

SQUARE-WAVE OFF

DS1374 toc01

VBAT (V)

SUPPLY CURRENT (nA)

5.34.84.33.83.32.82.31.8

350

400

450

500

550

300

1.3

VCC = 0V

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

_____________________________________________________________________

Typical Operating Characteristics

(VCC = +3.3V, TA= +25°C, unless otherwise noted.)

IBAT0SC2 vs. VBAT

SQUARE-WAVE ON

DS1374 toc02

400

450

500

550

600

650

700

750

800

350

VCC = 0V

VBAT (V)

SUPPLY CURRENT (nA)

5.34.84.33.83.32.82.31.81.3

IBATOSC1 vs. TEMPERATURE

VBAT = 3.0V

DS1374 toc03

TEMPERATURE (°C)

SUPPLY CURRENT (nA)

806040200-20

400

425

450

475

375

-40

VCC = 0V

ICCA vs. VCC

(SQUARE-WAVE ON)

DS1374 toc04

VCC (V)

SUPPLY CURRENT (μA)

5.34.83.8 4.32.8 3.32.3

100

125

150

175

200

225

250

275

1.8

OSCILLATOR FREQUENCY vs. VBACKUP

DS1374 toc05

VBACKUP (V)

FREQUENCY (Hz)

5.34.84.33.83.32.82.31.8

32768.3

32768.4

32768.5

32768.6

32768.7

32768.8

32768.2

32768.1

32768.0

1.3

VCC = 0V

VCC FALLING vs. RST DELAY

DS1374 toc06

VCC FALLING (V/ms)

RESET DELAY (μs)

1010.10

100

1000

0.1

0.01 100

VCC = 3.0V TO 0V

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

8 _____________________________________________________________________

Pin Description

µSOP SO NAME FUNCTION

1, 2 — X1, X2

Connections for a Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is designed for

operation with a crystal having a specified load capacitance (CL) of 6pF. Pin X1 is the input to the

oscillator and can optionally be connected to an external 32.768kHz oscillator. The output of the internal

oscillator, pin X2, is floated if an external oscillator is connected to pin X1.

313V

BACKUP

Connection for a Secondary Power Supply. This supply is used to operate the oscillator and counters

when VCC is absent. Supply voltage must be held between 1.3V and 3.7V (-18 and -3) or 1.3V and 5.5V

(-33) for proper operation. This pin can be connected to a primary cell such as a lithium cell.

Additionally, this pin can be connected to a rechargeable cell or a super cap when used with the trickle-

charge feature. UL recognized to ensure against reverse charging when used with a lithium battery. This

pin must be grounded if not used.

414RST

Active-Low, Open-Drain Output with a Debounced Pushbutton Input. This pin can be activated by a

pushbutton reset request, a watchdog alarm condition, or a power-fail event. It has an internal 50kΩ

pullup resistor. No external resistors should be connected. If the crystal oscillator is disabled, the startup

time of the oscillator is added to the tRST delay.

5 15 GND Ground

6 16 SDA Serial Data Input/Output. SDA is the input/output for the 2-wire serial interface. The SDA pin is open

drain and requires an external pullup resistor.

7 1 SCL Serial Clock Input. SCL is the clock input for the 2-wire serial interface and is used to synchronize data

movement on the serial interface.

82 INT Interupt. This pin is used to output the alarm interrupt or the watchdog reset signal. It is active-low open

drain and requires an external pullup resistor.

9 3 SQW Square-Wave Output. This pin is used to output the programmable square-wave signal. It is open drain

and requires an external pullup resistor.

10 4 VCC DC Power for Primary Power Supply

— 5–12 N.C. No Connection. Must be connected to ground.

CLOCK

DIVIDER

32-BIT

COUNTER

MUX

4.096kHz

1Hz

8.192kHz

32.768kHz 1Hz/4.096kHz

ALARM/

WATCHDOG

STAT/CTRL/

TRICKLE

24-BIT

COUNTER

INT

CONTROL

RST

CONTROL

2-WIRE

INTERFACE

POWER

CONTROL

AND

TRICKLE

CHARGE

VCC

VBACKUP

GND

SDA

SCL RST

SQW

INT

DS1374

Figure 4. Functional Diagram

Detailed Description

The DS1374 is a real-time clock with an I2C serial inter-

face. It provides elapsed seconds from a user-defined

starting point in a 32-bit counter (Figure 4). A 24-bit

counter can be configured as either a watchdog

counter or an alarm counter. An on-chip oscillator cir-

cuit uses a customer-supplied 32.768kHz crystal to

keep time. A power-control circuit switches operation

from VCC to VBACKUP and back when power on VCC is

cycled. The oscillator and counters continue to operate

when powered by either supply. If a rechargeable

backup supply is used, a trickle charger can be

enabled to charge the backup supply while VCC is on.

Oscillator Circuit

The DS1374 uses an external 32.768kHz crystal. The

oscillator circuit does not require any external resistors

or capacitors to operate. Table 1 specifies several crys-

tal parameters for the external crystal. Figure 5 shows a

functional schematic of the oscillator circuit. The startup

time is usually less than 1 second when using a crystal

with the specified characteristics.

Clock Accuracy

Clock accuracy is dependent upon the accuracy of the

crystal and the accuracy of the match between the

capacitive load of the oscillator circuit and the capacitive

load for which the crystal was trimmed. Additional error

is added by crystal frequency drift caused by tempera-

ture shifts. External circuit noise coupled into the oscilla-

tor circuit can result in the clock running fast. Figure 6

shows a typical PC board layout for isolating the crystal

and oscillator from noise. Refer to

Application Note 58:

Crystal Considerations with Dallas Real-Time Clocks

for

detailed information.

DS1374C Only

The DS1374C integrates a standard 32,768Hz crystal

into the package. Typical accuracy at nominal VCC and

25°C is approximately 10ppm. See

Application Note 58

for information about crystal accuracy vs. temperature.

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

_____________________________________________________________________ 9

COUNTDOWN

CHAIN

X1 X2

CL1CL2

CRYSTAL

RTC

REGISTERS

DS1374

Figure 5. Oscillator Circuit Showing Internal Bias Network

LOCAL GROUND PLANE (LAYER 2)

NOTE: AVOID ROUTING SIGNALS IN THE CROSSHATCHED AREA (UPPER LEFT-HAND

QUADRANT) OF THE PACKAGE UNLESS THERE IS A GROUND PLANE BETWEEN THE

SIGNAL LINE AND THE PACKAGE.

CRYSTAL

GND

Figure 6. Layout Example

PARAMETER SYMBOL MIN TYP MAX UNITS

Nominal

Frequency fO32.768 kHz

Series

Resistance ESR 45 kΩ

Load

Capacitance CL6pF

Table 1. Crystal Specifications*

The crystal, traces, and crystal input pins should be isolated

from RF generating signals. Refer to

Application Note 58:

Crystal Considerations for Dallas Real-Time Clocks

for addi-

tional specifications

DS1374

Power Control

The power-control function is provided by a precise,

temperature-compensated voltage reference and a

comparator circuit that monitors the VCC level. The

device is fully accessible and data can be written and

read when VCC is greater than VPF. However, when

VCC falls below VPF, the internal clock registers are

blocked from any access. If VPF is less than VBACKUP,

the device power is switched from VCC to VBACKUP

when VCC drops below VPF. If VPF is greater than

VBACKUP, the device power is switched from VCC to

VBACKUP when VCC drops below VBACKUP. The regis-

ters are maintained from the VBACKUP source until VCC

is returned to nominal levels (Table 1). After VCC

returns above VPF, read and write access is allowed

after RST goes high (Figure 1).

Address Map

Table 3 shows the address map for the DS1374 regis-

ters. During a multibyte access, the address pointer

wraps around to location 00h when it reaches the end of

the register space (08h). On an I2C START, STOP, or

address pointer incrementing to location 00h, the current

time is transferred to a second set of registers. These

secondary registers read the time information, while the

clock continues to run. This eliminates the need to reread

the registers in case of an update of the main registers

during a read.

Time-of-Day Counter

The time-of-day counter is a 32-bit up counter that

increments once per second when the oscillator is run-

ning. The contents can be read or written by accessing

the address range 00h–03h. When the counter is read,

the current time of day is latched into a register, which

is output on the serial data line while the counter contin-

ues to increment.

Note: Writing to any TOD register will reset the 1Hz

square wave output.

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

10 ____________________________________________________________________

SUPPLY CONDITION READ/WRITE

ACCESS

POWERED

VCC < VPF, VCC < VBACKPUP No VBACKUP

VCC < VPF, VCC > VBACKUP No VCC

VCC > VPF, VCC < VBACKUP Yes VCC

VCC > VPF, VCC > VBACKUP Yes VCC

Table 2. Power Control

ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION

00H TOD Counter Byte 0 Time-of-Day Counter

01H TOD Counter Byte 1 Time-of-Day Counter

02H TOD Counter Byte 2 Time-of-Day Counter

03H TOD Counter Byte 3 Time-of-Day Counter

04H WD/ALM Counter Byte 0 Watchdog/Alarm Counter

05H WD/ALM Counter Byte 1 Watchdog/Alarm Counter

06H WD/ALM Counter Byte 2 Watchdog/Alarm Counter

07H EOSC WACE WD/ALM BBSQW WDSTR RS2 RS1 AIE Control

08H OSF 0 0 0 0 0 0 AF Status

09H TCS3 TCS2 TCS1 TCS0 DS1 DS0 ROUT1 ROUT0 Trickle Charger

Table 3. Address Map

Note: Unless otherwise specified, the state of the registers is not defined when power is first applied.

Watchdog/Alarm Counter

The contents of the watchdog/alarm counter, which is a

separate 24-bit down counter, are accessed in the

address range 04h–06h. When this counter is written, the

counter and a seed register are loaded with the desired

value. When the counter is to be reloaded, it uses the

value in the seed register. When the counter is read, the

current counter value is latched into a register, which is

output on the serial data line while the counter continues

to decrement.

IIf the counter is not needed, it can be disabled and

used as a 24-bit cache of NV RAM by setting the

WACE bit in the control register to logic 0. If all 24 bits

of the watchdog/alarm counter are written to zero, the

counter is disabled, independent of the WACE bit set-

ting. When the watchdog counter is is written to a

nonzero value, and WACE is written to logic 1, the func-

tion of the counter is determined by the WD/ALM bit.

When the WD/ALM bit in the control register is set to

logic 0, the WD/ALM counter decrements every second

until it reaches zero. At this point, the AF bit in the sta-

tus register is set to 1 and the counter is reloaded and

restarted. AF remains set until cleared by writing it to 0.

If AIE = 1, the INT pin goes active whenever AF = 1.

WDSTR does not affect operation when WD/ALM = 0.

When the WD/ALM bit is set to logic 1, the WD/ALM

counter decrements every 1/4096 of a second (approx-

imately every 244us) until it reaches zero. When any of

the watchdog counters bytes are read, the seed value

is reloaded and the counter restarts. Writing to the

watchdog counter updates the seed value and reloads

the counter with the new seed value. When the counter

reaches zero, the AF bit is set and the counter stops.

If WDSTR = 0, the RST pin pulses low for 250ms, and

accesses to the device are inhibited. At the end of the

250ms pulse, the AF bit is cleared to zero, the RST pin

becomes high impedance, and read/write access to

the device is enabled.

If WDSTR = 1 and the counter reaches zero, the AF bit

is set and the counter stops. If AIE = 0, AF remains set

until cleared by writing it to 0. If AIE = 1, the INT pin

pulses low for 250ms. At the end of the 250ms pulse,

the AF bit is cleared and INT becomes high impedance.

The 250ms pulse on INT or RST cannot be truncated by

writing either AF or AIE to zero during the low time. If the

INT counter is written during the 250ms pulse, the

counter starts decrementing upon the pulse completion.

The watchdog and alarm function operates from VCC or

VBAT. When the AF bit is set, INT is pulled low when the

device is powered by VCC or VBAT.

Note: WACE must be toggled from logic 0 to logic 1

after the watchdog counter is written from a zero to a

nonzero value.

Power-Up/Power-Down Reset and

Pushbutton Reset Functions

A precision temperature-compensated reference and

comparator circuit monitors the status of VCC. When an

out-of-tolerance condition occurs, an internal power-fail

signal is generated that forces the RST pin low and

blocks read/write access to the DS1374. When VCC

returns to an in-tolerance condition, the RST pin is held

low for 250ms to allow the power supply to stabilize. If

the EOSC bit is set to a logic 1 (to disable the oscillator in

battery-backup mode), the reset signal is kept active for

250ms plus the startup time of the oscillator.

The DS1374 provides for a pushbutton switch to be con-

nected to the RST output pin. When the DS1374 is not in

a reset cycle, it continuously monitors the RST signal for

a low-going edge. If an edge is detected, the DS1374

debounces the switch by pulling the RST pin low and

inhibits read/write access. After the internal 250ms timer

has expired, the device continues to monitor the RST

line. If the line is still low, the DS1374 continues to moni-

tor the line, looking for a rising edge. Upon detecting

release, the DS1374 forces the RST pin low and holds it

low for an additional 250ms.

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

____________________________________________________________________ 11

Special Purpose Registers

The DS1374 has two additional registers (07h–08h) that

control the WD/ALM counter and the square-wave, inter-

rupt, and reset outputs.

Control Register (07h)

Bit 7/Enable Oscillator (EOSC). When set to logic 0,

the oscillator is started. When set to logic 1, the oscilla-

tor is stopped. When this bit is set to logic 1, the oscilla-

tor is stopped and the DS1374 is placed into a

low-power standby mode (IDDR). This bit is clear (logic

0) when power is first applied. When the DS1374 is

of the state of the EOSC bit.

Bit 6/WD/AALLMMCounter Enable (WACE). When set to

logic 1, the WD/ALM counter is enabled. When set to

logic 0, the WD/ALM counter is disabled, and the 24

bits can be used as NV RAM. This bit is clear (logic 0)

when power is first applied.

Bit 5/WD/AALLMMCounter Select (WD/ALM). When set to

logic 0, the counter decrements every second until it

reaches zero and is then reloaded and restarted. When

set to logic 1, the WD/ALM counter decrements every

1/4096 of a second (approximately every 244µs) until it

reaches zero, sets the AF bit in the status register, and

stops. If any of the WD/ALM counter registers are

accessed before the counter reaches zero, the counter

is reloaded and restarted. This bit is clear (logic 0)

when power is first applied.

Bit 4/Battery-Backed Square-Wave Enable (BBSQW).

This bit, when set to logic 1, enables the square-wave

output when VCC is absent and when the DS1374 is

being powered by the VBACKUP pin. When BBSQW is

logic 0, the SQW pin goes high impedance when VCC

falls below the power-fail trip point. This bit is disabled

(logic 0) when power is first applied.

Bit 3/Watchdog Reset Steering Bit (WDSTR). This bit

selects which output pin the watchdog-reset signal

occurs on. When the WDSTR bit is set to logic 0, a

250ms pulse occurs on the RST pin if WD/ALM = 1 and

the WD/ALM counter reaches zero. The 250ms reset

pulse occurs on the INT pin when the WDSTR bit is set

to logic 1. This bit is logic 0 when power is first applied.

Bits 2, 1/Rate Select (RS2 and RS1). These bits con-

trol the frequency of the square-wave output when the

square wave has been enabled. Table 4 shows the

square-wave frequencies that can be selected with the

RS bits. These bits are both set (logic 1) when power is

first applied.

Bit 0/Alarm Interrupt Enable (AIE). When set to logic

1, this bit permits the alarm flag (AF) bit in the status

logic 0 or INTCN is set to logic 0, the AF bit does not

initiate the INT signal. If the WD/ALM bit is set to logic 1

and the AF flag is set, writing AIE to zero does not trun-

cate the 250ms pulse on the INT pin. The AIE bit is at

logic 0 when power is first applied. The INT output is

available while the device is powered by either supply.

RS2 RS1 SQUARE-WAVE OUTPUT FREQUENCY

0 0 1Hz

0 1 4.096kHz

1 0 8.192kHz

1 1 32.768kHz

Table 4. Square-Wave Output Frequency

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

12 ____________________________________________________________________

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

EOSC WACE WD/ALM BBSQW WDSTR RS2 RS1 AIE

DS1374

Status Register (08h)

Bit 7/Oscillator Stop Flag (OSF). A logic 1 in this bit

indicates that the oscillator either is stopped or was

stopped for some period of time and can be used to

judge the validity of the timekeeping data. This bit is set

to logic 1 any time the oscillator stops. The following

are examples of conditions that can cause the OSF bit

to be set:

1) The first time power is applied.

2) The voltage present on both VCC and VBACKUP are

insufficient to support oscillation.

3) The EOSC bit is turned off.

4) External influences on the crystal (i.e., noise, leak-

age, etc.).

This bit remains at logic 1 until written to logic 0.

Bit 0/Alarm Flag (AF). A logic 1 in the alarm flag bit

indicates that the WD/ALM counter reached zero. If

WD/ALM is set to zero and the AIE bit = 1, the INT pin

goes low and stays low until AF is cleared. AF is

cleared when written to logic 0. This bit can only be

written to logic 0. Attempting to write logic 1 leaves the

value unchanged. If WD/ALM is set to 1 and the AIE

bit = 1, the INT pin pulses low for 250ms when the

WD/ALM counter reaches zero and sets AF = 1. At the

pulse completion, the DS1374 clears the AF bit to zero.

If the 250ms pulse is active, writing AF to zero does not

truncate the pulse.

Trickle-Charge Register (10h)

The simplified schematic in Figure 7 shows the basic

components of the trickle charger. The trickle-charge

select (TCS) bits (bits 4–7) control the selection of the

trickle charger. To prevent accidental enabling, only a

pattern of 1010 enables the trickle charger. All other

patterns disable the trickle charger. The trickle charger

is disabled when power is first applied. The diode

select (DS) bits (bits 2, 3) select whether or not a diode

is connected between VCC and VBACKUP. If DS is 01,

no diode is selected; if DS is 10, a diode is selected.

The ROUT bits (bits 0, 1) select the value of the resistor

connected between VCC and VBACKUP. Table 5 shows

the resistor selected by the resistor select (ROUT) bits

and the diode selected by the diode select (DS) bits.

Warning: The ROUT value of 250Ωmust not be select-

ed whenever VCC is greater than 3.63V.

The user determines diode and resistor selection

according to the maximum current desired for battery or

super cap charging. The maximum charging current can

be calculated as illustrated in the following example.

Assume that a system power supply of 3.3V is applied

to VCC and a super cap is connected to VBACKUP. Also

assume the trickle charger has been enabled with a

diode and resistor R2 between VCC and VBACKUP. The

maximum current IMAX would therefore be calculated

as follows:

IMAX = (3.3V - diode drop) / R2 ≈(3.3V - 0.7V) / 2kΩ≈

1.3mA

As the super cap changes, the voltage drop between

VCC and VBACKUP decreases and therefore the charge

current decreases.

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

OSF000000AF

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

____________________________________________________________________ 13

TCS3 TCS2 TCS1 TCS0 DS1 DS0 ROUT1 ROUT0 FUNCTION

X X X X 0 0 X X Disabled

X X X X 1 1 X X Disabled

XXXXXX00Disabled

1 0 1 0 0 1 0 1 No diode, 250Ω resistor

1 0 1 0 1 0 0 1 One diode, 250Ω resistor

1 0 1 0 0 1 1 0 No diode, 2kΩ resistor

1 0 1 0 1 0 1 0 One diode, 2kΩ resistor

1 0 1 0 0 1 1 1 No diode, 4kΩ resistor

1 0 1 0 1 0 1 1 One diode, 4kΩ resistor

0 0 0 0 0 0 0 0 Power-on reset value

Table 5. Trickle Charge Register

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

14 ____________________________________________________________________

I2C Serial Data Bus

The DS1374 supports the I2C bus protocol. A device

that sends data onto the bus is defined as a transmitter

and a device receiving data is a receiver. The device

that controls the message is called a master. The

devices that are controlled by the master are slaves. A

master device that generates the serial clock (SCL),

controls the bus access, and generates the START and

STOP conditions must control the bus. The DS1374

operates as a slave on the I2C bus. Connections to the

bus are made through the open-drain I/O lines SDA

and SCL. A standard mode (100kHz max clock rate)

and a fast mode (400kHz max clock rate) are defined

within the bus specifications. The DS1374 works in both

modes.

The following bus protocol has been defined (Figure 8):

• Data transfer can be initiated only when the bus is

not busy.

• During data transfer, the data line must remain sta-

ble whenever the clock line is high. Changes in the

data line while the clock line is high can be interpret-

ed as control signals.

STOP

CONDITION

OR REPEATED

START

CONDITION

REPEATED IF MORE BYTES

ARE TRANSFERED

ACK

START

CONDITION

ACK

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

ACKNOWLEDGEMENT

SIGNAL FROM RECEIVER

SLAVE ADDRESS

MSB

SCL

SDA

R/W

DIRECTION

BIT

12 678 9 12 893–7

Figure 8. I2C Data Transfer Overview

BIT 7

TCS3

1 OF 16 SELECT

NOTE: ONLY 1010b

ENABLES CHARGER

1 OF 2

SELECT

VCC VBACKUP

250Ω

TCS0-3 = TRICKLE CHARGER SELECT

DS0-1 = DIODE SELECT

TOUT0-1 = RESISTOR SELECT

2kΩ

4kΩ

1 OF 3

SELECT

BIT 6

TCS2

BIT 5

TCS1

BIT 4

TCS0

BIT 3

DS1

BIT 2

DS0

BIT 1

ROUT1

BIT 0

ROUT0

Figure 7. Programmable Trickle Charger

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

____________________________________________________________________ 15

S 1101000 0 A XXXXXXXX A XXXXXXXX A XXXXXXXX A XXXXXXXX P

DATA TRANSFERRED

(X+1 Bytes + Acknowledge)

SLAVE

ADDRESS

S - START

A - ACKNOWLEDGE

P - STOP

R/W - READ/WRITE OR

DIRECTION BIT

DATA (n)

ADDRESS (n) DATA (n + 1) DATA (n + x)

R/W

Figure 9. I2C Write Protocol

S 1101000 1 A XXXXXXXX A XXXXXXXX A XXXXXXXX A XXXXXXXX /A

DATA TRANSFERRED

(X+1 Bytes + Acknowledge)

SLAVE

ADDRESS

S - START

A - ACKNOWLEDGE

P - STOP

/A - NOT ACKNOWLEDGE

R/W - READ/WRITE OR

DIRECTION BIT

DATA (n) DATA (n + 1) DATA (n + x)DATA (n + 2)

R/W

Figure 10. I2C Read Protocol

Accordingly, the following bus conditions have been

defined:

Bus not busy: Both data and clock lines remain

high.

Start data transfer: A change in the state of the

data line from high to low, while the clock line is

high, defines a START condition.

Stop data transfer: A change in the state of the

data line from low to high, while the clock line is

high, defines a STOP condition.

Data valid: The state of the data line represents

valid data when, after a START condition, the data

line is stable for the duration of the high period of

the clock signal. The data on the line must be

changed during the low period of the clock signal.

There is one clock pulse per bit of data.

Each data transfer is initiated with a START condi-

tion and terminated with a STOP condition. The

number of data bytes transferred between the

START and the STOP conditions is not limited, and

is determined by the master device. The informa-

tion is transferred byte-wise and each receiver

acknowledges with a ninth bit. A standard mode

(100kHz clock rate) and a fast mode (400kHz clock

rate) are defined within the I2C bus specifications.

Acknowledge: Each receiving device, when

addressed, is obliged to generate an acknowledge

after the reception of each byte. The master device

must generate an extra clock pulse that is associat-

ed with this acknowledge bit.

A device that acknowledges must pull down the

SDA line during the acknowledge clock pulse in

such a way that the SDA line is stable low during

the high period of the acknowledge-related clock

pulse. Setup and hold times must be considered. A

master must signal an end of data to the slave by

not generating an acknowledge bit on the last byte

that has been clocked out of the slave. In this case,

the slave must leave the data line high to enable

the master to generate the STOP condition.

Figures 9 and 10 detail how data transfer is accom-

plished on the 2-wire bus. Depending on the state of

the R/Wbit, two types of data transfer are possible:

Data transfer from a master transmitter to a

slave receiver. The first byte transmitted by the

master is the slave address. Next follows a number

of data bytes. The slave returns an acknowledge

bit after each received byte.

Data transfer from a slave transmitter to a mas-

ter receiver. The master transmits the first byte

(the slave address). The slave then returns an

acknowledge bit. Next follows a number of data

bytes transmitted by the slave to the master. The

master returns an acknowledge bit after all

received bytes other than the last byte. At the end

of the last received byte, a “not acknowledge” is

returned.

The master device generates the serial clock puls-

es and the START and STOP conditions. A transfer

is ended with a STOP condition or with a repeated

START condition. Since a repeated START condi-

tion is also the beginning of the next serial transfer,

the bus is not released.

The DS1374 can operate in the following two modes:

Slave Receiver Mode (Write Mode): Serial data

and clock data are received through SDA and SCL.

After each byte is received, an acknowledge bit is

transmitted. START and STOP conditions are rec-

ognized as the beginning and end of a serial trans-

fer. Address recognition is performed by hardware

after reception of the slave address and direction

bit. The slave address byte is the first byte

received after the master generates a START con-

dition. The slave address byte contains the 7-bit

DS1374 address, which is 1101000, followed by

the direction bit (R/W), which is zero for a write.

After receiving and decoding the slave address

byte, the DS1374 outputs an acknowledge on SDA.

DS1374

After the DS1374 acknowledges the slave address

+ write bit, the master transmits a register address

to the DS1374. This sets the register pointer on the

DS1374, with the DS1374 acknowledging the trans-

fer. The master can then transmit zero or more

bytes of data, with the DS1374 acknowledging

each byte received. The register pointer increments

after each data byte is transferred. The master gen-

erates a STOP condition to terminate the data write.

Slave Transmitter Mode (Read Mode): The first

byte is received and handled as in the slave receiv-

er mode. However, in this mode, the direction bit

indicates that the transfer direction is reversed.

Serial data is transmitted on SDA by the DS1374,

while the serial clock is input on SCL. START and

STOP conditions are recognized as the beginning

and end of a serial transfer. Address recognition is

performed by hardware after reception of the slave

address and direction bit. The slave address byte

is the first byte received after the START condition

is generated by the master. The slave address byte

contains the 7-bit DS1374 address, which is

1101000, followed by the direction bit (R/W), which

is 1 for a read. After receiving and decoding the

slave address byte, the DS1374 outputs an

acknowledge on SDA. The DS1374 then begins to

transmit data starting with the register address

pointed to by the register pointer. If the register

pointer is not written to before the initiation of a

read mode, the first address that is read is the last

one stored in the register pointer. The DS1374 must

receive a not acknowledge to end a read.

Handling, PC Board Layout, and

Assembly

The DS1374C package contains a quartz tuning-fork

crystal. Pick-and-place equipment can be used, but

precautions should be taken to ensure that excessive

shocks are avoided. Ultrasonic cleaning should be

avoided to prevent damage to the crystal.

Avoid running signal traces under the package, unless

a ground plane is placed between the package and the

signal line. All no connect (N.C.) pins must be connect-

ed to ground.

The SO package can be reflowed as long as the peak

temperature does not exceed 240°C. Peak reflow tem-

perature (≥230°C) duration should not exceed 10 sec-

onds, and the total time above 200°C should not

exceed 40 seconds (30 seconds nominal). Exposure to

reflow is limited to 2 times maximum.

Moisture-sensitive packages are shipped from the facto-

ry dry-packed. Handling instructions listed on the pack-

age label must be followed to prevent damage during

reflow. Refer to the IPC/JEDEC J-STD-020B standard for

moisture-sensitive device (MSD) classifications.

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

16 ____________________________________________________________________

VCC

SQW

INT

SCLRST

VBACKUP

TOP VIEW

SDAGND

DS1374

μSOP

SCL 1

SDA

GND

VBACKUP

INT

VCC

SQW

N.C.

RST

N.C.

SO (0.300")

DS1374C

Pin Configurations

DS1374

I2C, 32-Bit Binary Counter Watchdog RTC with

Trickle Charger and Reset Input/Output

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________

is a registered trademark of Dallas Semiconductor Corporation.

Chip Information

TRANSISTOR COUNT: 11,036

PROCESS: CMOS

SUBSTRATE CONNECTED TO GROUND

Thermal Information

Theta-JA: 221°C/W (µSOP)

Theta-JC: 39°C/W (µSOP)

Theta-JA: 73°C/W (16 SO)

Theta-JC: 23°C/W (16 SO)

Ordering Information (continued)

PART TEMP RANGE VOLTAGE (V) PIN-PACKAGE TOP MARK*

DS1374U-18 -40°C to +85°C 1.8 10 µSOP DS1374-18

DS1374U-18+ -40°C to +85°C 1.8 10 µSOP DS1374-18

DS1374U-3 -40°C to +85°C 3.0 10 µSOP DS1374-3

DS1374U-3+ -40°C to +85°C 3.0 10 µSOP DS1374-3

DS1374U-3/T&R -40°C to +85°C 3.0 10 µSOP/Tape and Reel DS1374-3

DS1374U-3+T&R -40°C to +85°C 3.0 10 µSOP/Tape and Reel DS1374-3

DS1374U-33 -40°C to +85°C 3.3 10 µSOP DS1374-33

DS1374U-33+ -40°C to +85°C 3.3 10 µSOP DS1374-33

DS1374U-33/T&R -40°C to +85°C 3.3 10 µSOP/Tape and Reel DS1374-33

DS1374U-33+T&R -40°C to +85°C 3.3 10 µSOP/Tape and Reel DS1374-33

Denotes a lead(Pb)-free/RoHS-compliant device.

A "+" anywhere on the top mark denotes a lead-free device.

Package Information

For the latest package outline information and land patterns, go

to www.maxim-ic.com/packages.

PACKAGE TYPE PACKAGE CODE DOCUMENT NO.

16 SO (0.300”) W16-H2 21-0042

10 µSOP (3.0mm) U10+2 21-0061