Rainbow Electronics DS1342 User Manual

19-4998; Rev 0; 10/09

Typical Operating Circuit

Low-Current I2C RTCs for High-ESR Crystals

General Description

The DS1341/DS1342 low-current real-time clocks (RTCs) are timekeeping devices that provide an extremely low standby current, which permits longer life from a power supply. The DS1341/DS1342 support high-ESR crystals, which broaden the pool of usable crystals for the devices. The DS1341 uses a 6pF crystal, while the DS1342 uses a

12.5pF crystal. These devices are accessed through an I2C serial interface. Other features include two time-of-day alarms, two interrupt outputs, a programmable squarewave output, and a serial bus timeout mechanism.

The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either 24hr or 12hr format with an AM/PM indicator.

The DS1341/DS1342 also include an input for synchronization. When a reference clock (e.g., 60Hz power line or GPS 1PPS) is present at the CLKIN pin and the enable external clock input bit (ECLK) is set to 1, the DS1341/ DS1342 RTCs are frequency-locked to the external clock and the clock accuracy is determined by the external source. In case of external clock failure, the clock is switched to the crystal oscillator.

The devices are available in a lead(Pb)-free/RoHScompliant, 8-pin FSOP package. The devices support a

-40NC to +85NC extended temperature range.

Applications

Medical

Point of Sale (POS)

Telematics

Portable Instruments

Portable Audio

Automotive

Features

S Low Timekeeping Current of 250nA (typ)

S Compatible with Crystal ESR Up to 80kI

S Use Crystals with C

= 6pF (DS1341) or

CL = 12.5pF (DS1342)

S +1.8V to +5.5V Operating Voltage Range

S Maintain Time Down to +1.15V (typ)

S Fast (400kHz) I

S Bus Timeout for Lockup-Free Operation

S RTC Counts Seconds, Minutes, Hours, Day, Date,

C Interface

Month, and Year with Leap Year Compensation Valid Through 2099

S External Clock Source for Synchronization Clock

Reference (e.g., 32kHz, 50Hz/60Hz Power Line, GPS 1PPS)

S Two Time-of-Day Alarms with Two Interrupt

Outputs

S Programmable Square-Wave Output

S Industrial Temperature Range

S Small, 8-Pin µSOP Package

Ordering Information

PART TEMP RANGE

DS1341U+

DS1341U+T&R DS1342U+* DS1342U+T&R*

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

T&R = Tape and reel.

*Future product—contact factory for availability.

-40NC to +85NC 8 FSOP

PINPACKAGE

OSC

CL (pF)

6 6

12.5

DS1341/DS1342

CPU

_______________________________________________________________ Maxim Integrated Products 1

SCL

SDA

CLKIN/INTA

SQW/INTBX1X2

DS1341/DS1342

GND

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.

Pin Configuration

TOP VIEW

1 8 V

2 7 SQW/INTBX2

DS1341 DS1342

µSOP

SCLCLKIN/INTA 3 6

SDAGND 4 5

Low-Current I2C RTCs for High-ESR Crystals

ABSOLUTE MAXIMUM RATINGS

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

Operating Temperature Range .......................... -40NC to +85NC

Junction-to-Ambient Thermal

Resistance (BJA) (Note 1) ........................................ +221NC/W

Junction-to-Case Thermal

Resistance (BJC) (Note 1) ......................................... +39NC/W

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.

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.

Junction Temperature Maximum .....................................+150NC

Storage Temperature Range ............................ -55NC to +125NC

Soldering Temperature .........................Refer to the IPC/JEDEC

J-STD-020 Specification.

DS1341/DS1342

DC ELECTRICAL CHARACTERISTICS

(VCC = +1.8V to +5.5V, TA = -40NC to +85NC, unless otherwise noted.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Operating Voltage Range

Minimum Timekeeping Voltage V

Timekeeping Current: DS1341 CLKIN = GND or CLKIN = VCC (Note 4)

Logic 1 Input V

Logic 0 Input V

Input Leakage (SCL, CLKIN/INTA)

Output Leakage (CLKIN/INTA, SQW/INTB)

Output Logic 1 VOH = +1.0V (SQW /INTB)

Output Logic 0 VOL = +0.4V (SDA, CLKIN/INTA, SQW/INTB)

CCTMIN

CCT

Full operation (Note 3) 1.8 5.5 Timekeeping (Notes 3, 4) 1.3 5.5 TA = +25NC (Notes 3, 4) VCC = +3.0V, EGFIL = 0, DOSF = 1 220 500 VCC = +5.5V 250 600 VCC = +3.0V, EGFIL = 1, DOSF = 0 280 560 VCC = +5.5V 320 700

(Note 2)

(Note 2) -0.3

ECLK = 1, VIN = 0V to V

ECLK = A1IE = A2IE = 0 -1.0 +1.0

VCC R 1.8V, INTCN = 0 VCC R 1.3V, INTCN = 0

VCC R 1.8V

VCC R 1.3V (Note 5)

0.7 x V

-0.1 +0.1

-3.0 mA

-250

3.0 mA

250

1.15 1.3 V

VCC +

0.3

0.3 x V

Low-Current I2C RTCs for High-ESR Crystals

AC ELECTRICAL CHARACTERISTICS

(VCC = +1.8V to +5.5V, TA = -40NC to +85NC, unless otherwise noted.) (Note 2, Figure 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

SCL Clock Frequency f

Bus Free Time Between a STOP and START Condition

Hold Time (Repeated) START Condition

Low Period of SCL Clock t High Period of SCL Clock t Data Hold Time t Data Setup Time t

Setup Time for a Repeated START Condition

Rise Time of Both SDA and SCL Signals

Fall Time for Both SDA and SCL Signals

Setup Time for STOP Condition t

Capacitive Load for Each Bus Line

I/O Capacitance C SCL Spike Suppression t Oscillator Stop Flag (OSF) Delay t Timeout Interval t

HD:STA

HD:DAT

SU:DAT

SU:STA

SU:STO

TIMEOUT

SCL

BUF

LOW

HIGH

I/O

OSF

(Note 6) 400 kHz

(Note 7) 0.6

(Notes 8, 9) 0 0.9 (Note 10) 100 ns

(Note 11)

(Note 11) 400 pF

(Note 12) 25 100 ms (Note 13) 25 35 ms

1.3

0.6

20 +

0.1C

20 +

0.1C

0.6

10 pF 30 ns

DS1341/DS1342

Fs Fs Fs

300 ns

CRYSTAL PARAMETERS

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Nominal Frequency f Series Resistance ESR 35 80

Load Capacitance C

Note 2: Limits at -40NC are guaranteed by design and not production tested. Note 3: Voltage referenced to ground. Note 4: Specified with I2C bus inactive. Oscillator operational, INTCN = 1, ECLK = 0. Note 5: Applies to CLKIN/INTA and SQW/INTB only. Note 6: The minimum SCL clock frequency is limited by the bus timeout feature, which resets the serial bus interface if SCL is

held low for t

Note 7: After this period, the first clock pulse is generated. Note 8: A device must internally provide a hold time of at least 300ns for the SDA signal (referred to the V

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

Note 9: The maximum t Note 10: A fast-mode device can be used in a standard-mode system, but the requirement t

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 t 1250ns before the SCL line is released.

TIMEOUT

need only be met if the device does not stretch the low period (t

HD:DAT

DS1341 6

DS1342 12.5

SU:DAT

32.768 kHz

of the SCL sig-

IHMIN

) of the SCL signal.

LOW

R to 250ns must then be

RMAX

+ t

= 1000 + 250 =

SU:DAT

Low-Current I2C RTCs for High-ESR Crystals

Note 11: CB is the total capacitance of one bus line, including all connected devices, in pF. Note 12: The parameter t

range of 2.4V P VCC P V

Note 13: The DS1341/DS1342 can detect any single SCL clock held low longer than t

in reset state and can receive a new START condition when SCL is held low for at least t detects this condition, the SDA output is released. The oscillator must be running for this function to work.

SDA

DS1341/DS1342

SCL

NOTE: TIMING IS REFERENCED TO V

BUF

HD:STA

STOP START REPEATED

is the period of time the oscillator must be stopped for the OSF flag to be set over the voltage

OSF

CCMAX

TIMEOUTMIN

. The devices’ I2C interface is

TIMEOUTMAX

ILMAX

LOW

AND V

IHMIN

HD:DAT

HIGH

SU:DAT

START

SU:STA

HD:STA

. Once the device

SU:STO

Figure 1. Data Transfer on I2C Serial Bus

Low-Current I2C RTCs for High-ESR Crystals

Functional Diagram

DS1341/DS1342

32.768kHz

8.192kHz

4.096kHz

/4 /32 EXTSYNC

CONTROL LOGIC

128Hz OSC-1Hz

OSC-1Hz

EXT-1Hz

ALARM AND

CONTROL REGISTERS

CLOCK AND

CALENDAR REGISTERS

DIVIDER

MUX/

BUFFER

SQW/INTB

CLKIN/INTA

SCL

SDA

DS1341/DS1342

SERIAL BUS

INTERFACE AND

ADDRESS

Pin Description

PIN NAME FUNCTION

1 X1

2 X2

CLKIN/INTA

4 GND Ground

5 SDA

6 SCL Serial-Clock Input. SCL is used to synchronize data movement on the serial interface.

8 V

SQW/INTB

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 (DS1341) or 12.5pF (DS1342).

Clock Input/Active-Low Interrupt Output. This I/O pin is used to output an alarm interrupt or accept an external clock input to drive the RTC counter. In the output mode, this is an open drain and requires an external pullup resistor. If not used, connect this pin to ground.

Serial-Data Input/Output. SDA is the input/output pin for the I2C serial interface. The SDA pin is open drain and requires an external pullup resistor.

Square-Wave/Active-Low Interrupt Output. This pin is used to output a programmable square wave or an alarm interrupt signal. This is a CMOS push-pull output and does not require an external pullup resistor. If not used, this pin can be left unconnected.

DC Power Input. This pin should be decoupled using a 0.01FF or 0.1FF capacitor.

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