DS3231S#T&R - Maxim - Product.Network

AVAILABLE

Functional Diagrams

Pin Configurations appear at end of data sheet.

Functional Diagrams continued at end of data sheet.

UCSP is a trademark of Maxim Integrated Products, Inc.

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

General Description

The DS3231 is a low-cost, extremely accurate I2C real-

time clock (RTC) with an integrated temperature-

compensated crystal oscillator (TCXO) and crystal. The

device incorporates a battery input, and maintains accu-

rate timekeeping when main power to the device is inter-

rupted. The integration of the crystal resonator enhances

the long-term accuracy of the device as well as reduces

the piece-part count in a manufacturing line. The DS3231

is available in commercial and industrial temperature

ranges, and is offered in a 16-pin, 300-mil SO package.

The RTC maintains 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 the 24-hour or 12-hour format

with an AM/PM indicator. Two programmable time-of-

day alarms and a programmable square-wave output

are provided. Address and data are transferred serially

through an I2C bidirectional bus.

A precision temperature-compensated voltage refer-

ence and comparator circuit monitors the status of VCC

to detect power failures, to provide a reset output, and

to automatically switch to the backup supply when nec-

essary. Additionally, the RST pin is monitored as a

pushbutton input for generating a µP reset.

Applications

Servers Utility Power Meters

Telematics GPS

Features

♦Accuracy ±2ppm from 0°C to +40°C

♦Accuracy ±3.5ppm from -40°C to +85°C

♦Battery Backup Input for Continuous

Timekeeping

♦Operating Temperature Ranges

Commercial: 0°C to +70°C

Industrial: -40°C to +85°C

♦Low-Power Consumption

♦Real-Time Clock Counts Seconds, Minutes,

Hours, Day, Date, Month, and Year with Leap Year

Compensation Valid Up to 2100

♦Two Time-of-Day Alarms

♦Programmable Square-Wave Output

♦Fast (400kHz) I2C Interface

♦3.3V Operation

♦Digital Temp Sensor Output: ±3°C Accuracy

♦Register for Aging Trim

♦RST Output/Pushbutton Reset Debounce Input

♦Underwriters Laboratories (UL) Recognized

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

19-5170; Rev 8; 7/10

Ordering Information

PART TEMP RANGE PIN-PACKAGE

DS3231S# 0°C to +70°C 16 SO

DS3231SN# -40°C to +85°C 16 SO

Pin Configuration appears at end of data sheet.

Typical Operating Circuit

#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 device.

DS3231

VCC

SCL

RPU

RPU = tR/CB

RPU

INT/SQW

32kHz

VBAT

PUSHBUTTON

RESET

SDA

RST

N.C.

VCC

GND

VCC

μP

N.C.

SCL

SDA

RST

DS3231

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

ABSOLUTE MAXIMUM RATINGS

RECOMMENDED OPERATING CONDITIONS

(TA= TMIN to TMAX, unless otherwise noted.) (Notes 2, 3)

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, VBAT, 32kHz, SCL, SDA, RST,

INT/SQW Relative to Ground.............................-0.3V to +6.0V

Junction-to-Ambient Thermal Resistance (θJA) (Note 1)....73°C/W

Junction-to-Case Thermal Resistance (θJC) (Note 1) ......23°C/W

Operating Temperature Range

(noncondensing) .............................................-40°C to +85°C

Junction Temperature......................................................+125°C

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

Lead Temperature (soldering, 10s) .................................+260°C

Soldering Temperature (reflow, 2 times max)

Lead(Pb)-free...............................................................+260°C

Containing lead(Pb) .....................................................+240°C

(See the

Handling, PC Board Layout, and Assembly

section.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VCC 2.3 3.3 5.5 V

Supply Voltage VBAT 2.3 3.0 5.5 V

Logic 1 Input SDA, SCL VIH 0.7 x

VCC

VCC +

0.3 V

Logic 0 Input SDA, SCL VIL -0.3

0.3 x

VCC V

ELECTRICAL CHARACTERISTICS

(VCC = 2.3V to 5.5V, VCC = Active Supply (see Table 1), TA= TMIN to TMAX, unless otherwise noted.) (Typical values are at VCC =

3.3V, VBAT = 3.0V, and TA= +25°C, unless otherwise noted.) (Notes 2, 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VCC = 3.63V 200

Active Supply Current ICCA (Notes 4, 5) VCC = 5.5V 300 μA

VCC = 3.63V 110

Standby Supply Current ICCS

I2C bus inactive, 32kHz

output on, SQW output off

(Note 5) VCC = 5.5V 170

μA

VCC = 3.63V 575

Temperature Conversion Current ICCSCONV I2C bus inactive, 32kHz

output on, SQW output off VCC = 5.5V 650 μA

Power-Fail Voltage VPF 2.45 2.575 2.70 V

Logic 0 Output, 32kHz,

INT/SQW, SDA VOL I

OL = 3mA 0.4 V

Logic 0 Output, RST V

OL I

OL = 1mA 0.4 V

Output Leakage Current 32kHz,

INT/SQW, SDA ILO Output high impedance -1 0 +1 μA

Input Leakage SCL ILI -1 +1 μA

RST Pin I/O Leakage IOL RST high impedance (Note 6) -200 +10 μA

VBAT Leakage Current

(VCC Active) IBATLKG 25 100 nA

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.

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

ELECTRICAL CHARACTERISTICS (continued)

(VCC = 2.3V to 5.5V, VCC = Active Supply (see Table 1), TA= TMIN to TMAX, unless otherwise noted.) (Typical values are at VCC =

3.3V, VBAT = 3.0V, and TA= +25°C, unless otherwise noted.) (Notes 2, 3)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Output Frequency fOUT V

CC = 3.3V or VBAT = 3.3V 32.768 kHz

0°C to +40°C ±2

Frequency Stability vs.

Temperature (Commercial) f/fOUT

VCC = 3.3V or

VBAT = 3.3V,

aging offset = 00h >40°C to +70°C ±3.5

ppm

-40°C to <0°C ±3.5

0°C to +40°C ±2

Frequency Stability vs.

Temperature (Industrial) f/fOUT

VCC = 3.3V or

VBAT = 3.3V,

aging offset = 00h >40°C to +85°C ±3.5

ppm

Frequency Stability vs. Voltage f/V 1 ppm/V

-40°C 0.7

+25°C 0.1

+70°C 0.4

Trim Register Frequency

Sensitivity per LSB f/LSB Specified at:

+85°C 0.8

ppm

Temperature Accuracy Temp VCC = 3.3V or VBAT = 3.3V -3 +3 °C

First year ±1.0

Crystal Aging f/fOAfter reflow,

not production tested 0–10 years ±5.0 ppm

ELECTRICAL CHARACTERISTICS

(VCC = 0V, VBAT = 2.3V to 5.5V, TA= TMIN to TMAX, unless otherwise noted.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VBAT = 3.63V 70

Active Battery Current IBATA

EOSC = 0, BBSQW = 0,

SCL = 400kHz (Note 5) VBAT = 5.5V 150 μA

VBAT = 3.63V 0.84 3.0

Timekeeping Battery Current IBATT

EOSC = 0, BBSQW = 0,

EN32kHz = 1,

SCL = SDA = 0V or

SCL = SDA = VBAT (Note 5) VBAT = 5.5V 1.0 3.5

μA

VBAT = 3.63V 575

Temperature Conversion Current IBATTC

EOSC = 0, BBSQW = 0,

SCL = SDA = 0V or

SCL = SDA = VBAT V

BAT = 5.5V 650

μA

Data-Retention Current IBATTDR EOSC = 1, SCL = SDA = 0V, +25°C 100 nA

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

AC ELECTRICAL CHARACTERISTICS

(VCC = VCC(MIN) to VCC(MAX) or VBAT = VBAT(MIN) to VBAT(MAX), VBAT > VCC, TA= TMIN to TMAX, unless otherwise noted.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Fast mode 100 400

SCL Clock Frequency 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 7) 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 8, 9) tHD:DAT Standard mode 0 0.9 μs

Fast mode 100

Data Setup Time (Note 10) 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 11) tRStandard mode

20 +

0.1CB 1000

Fast mode 300

Fall Time of Both SDA and SCL

Signals (Note 11) tFStandard mode

20 +

0.1CB 300

Fast mode 0.6

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

Capacitive Load for Each Bus

Line CB (Note 11) 400 pF

Capacitance for SDA, SCL CI/O 10 pF

Pulse Width of Spikes That Must

Be Suppressed by the Input Filter tSP 30 ns

Pushbutton Debounce PBDB 250 ms

Reset Active Time tRST 250 ms

Oscillator Stop Flag (OSF) Delay tOSF (Note 12) 100 ms

Temperature Conversion Time tCONV 125 200 ms

POWER-SWITCH CHARACTERISTICS

(TA= TMIN to TMAX)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

VCC Fall Time; VPF(MAX) to

VPF(MIN) tVCCF 300 μs

VCC Rise Time; VPF(MIN) to

VPF(MAX) tVCCR 0 μs

Recovery at Power-Up tREC (Note 13) 250 300 ms

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Pushbutton Reset Timing

tRST

PBDB

RST

Power-Switch Timing

VCC

tVCCF tVCCR

tREC

VPF(MAX)

VPF VPF

VPF(MIN)

RST

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Data Transfer on I2C Serial Bus

SCL

NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN).

SDA

STOP START REPEATED

START

tBUF

tHD:STA

tHD:DAT tSU:DAT

tSU:STO

tHD:STA

tSP

tSU:STA

tHIGH

tLOW

WARNING: Negative undershoots below -0.3V while the part is in battery-backed mode may cause loss of data.

Note 2: Limits at -40°C are guaranteed by design and not production tested.

Note 3: All voltages are referenced to ground.

Note 4: ICCA—SCL clocking at max frequency = 400kHz.

Note 5: Current is the averaged input current, which includes the temperature conversion current.

Note 6: The RST pin has an internal 50kΩ(nominal) pullup resistor to VCC.

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 VIH(MIN) of the SCL signal)

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

Note 9: The maximum tHD:DAT needs only to be met if the device does not stretch the low period (tLOW) of the SCL signal.

Note 10: A fast-mode device can be used in a standard-mode system, but the requirement tSU:DAT ≥250ns must then 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 tR(MAX) + tSU:DAT = 1000 + 250 = 1250ns

before the SCL line is released.

Note 11: CB—total capacitance of one bus line in pF.

Note 12: 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

0.0V ≤VCC ≤VCC(MAX) and 2.3V ≤VBAT ≤3.4V.

Note 13: This delay applies only if the oscillator is enabled and running. If the EOSC bit is a 1, tREC is bypassed and RST immedi-

ately goes high. The state of RST does not affect the I2C interface, RTC, or TCXO.

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Typical Operating Characteristics

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

STANDBY SUPPLY CURRENT

vs. SUPPLY VOLTAGE

DS3231 toc01

VCC (V)

ICCS (μA)

5.04.54.03.53.02.5

100

125

150

2.0 5.5

RST ACTIVE

BSY = 0, SCL = SDA = VCC

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

DS3231 toc02

VBAT (V)

IBAT (μA)

5.34.33.3

0.7

0.8

0.9

1.0

1.1

1.2

0.6

2.3

VCC = 0V, BSY = 0,

SDA = SCL = VBAT OR VCC

EN32kHz = 1

EN32kHz = 0

SUPPLY CURRENT

vs. TEMPERATURE

DS3231 toc03

TEMPERATURE (°C)

IBAT (μA)

603510-15

0.7

0.8

0.9

1.0

0.6

-40 85

VCC = 0, EN32kHz = 1, BSY = 0,

SDA = SCL = VBAT OR GND

FREQUENCY DEVIATION

vs. TEMPERATURE vs. AGING VALUE

DS3231 toc04

TEMPERATURE (°C)

FREQUENCY DEVIATION (ppm)

603510-15

-30

-20

-10

-40

-40 85

127

-33

DELTA TIME AND FREQUENCY

vs. TEMPERATURE

TEMPERATURE (°C)

DELTA FREQUENCY (ppm)

DELTA TIME (MIN/YEAR)

807050 60-10 0 10 20 30 40-30 -20

-180

-160

-140

-120

-100

-80

-60

-40

-20

-200

-80

-60

-40

-20

-100

-40

DS3231 toc05

CRYSTAL

+20ppm

CRYSTAL

-20ppm

TYPICAL CRYSTAL,

UNCOMPENSATED

DS3231

ACCURACY

BAND

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Block Diagram

CLOCK AND CALENDAR

REGISTERS

USER BUFFER

(7 BYTES)

VOLTAGE REFERENCE;

DEBOUNCE CIRCUIT;

PUSHBUTTON RESET

I2C INTERFACE AND

ADDRESS REGISTER

DECODE

POWER CONTROL

VCC

VBAT

GND

SCL

SDA

TEMPERATURE

SENSOR

CONTROL LOGIC/

DIVIDER

ALARM, STATUS, AND

CONTROL REGISTERS

OSCILLATOR AND

CAPACITOR ARRAY

32kHz

INT/SQW

SQUARE-WAVE BUFFER;

INT/SQW CONTROL

RST

VCC

DS3231

1Hz

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Pin Description

PIN NAME FUNCTION

1 32kHz

32kHz Output. This open-drain pin requires an external pullup resistor. When enabled, the output operates

on either power supply. It may be left open if not used.

2 VCC DC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1μF to 1.0μF capacitor.

If not used, connect to ground.

3INT/SQW

Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor

connected to a supply at 5.5V or less. This multifunction pin is determined by the state of the INTCN bit in

the Control Register (0Eh). When INTCN is set to logic 0, this pin outputs a square wave and its frequency

is determined by RS2 and RS1 bits. When INTCN is set to logic 1, then a match between the timekeeping

registers and either of the alarm registers activates the INT/SQW pin (if the alarm is enabled). Because the

INTCN bit is set to logic 1 when power is first applied, the pin defaults to an interrupt output with alarms

disabled. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC. If not used, this pin can

be left unconnected.

4RST

Active-Low Reset. This pin is an open-drain input/output. It indicates the status of VCC relative to the

VPF specification. As VCC falls below VPF, the RST pin is driven low. When VCC exceeds VPF, for tRST, the RST

pin is pulled high by the internal pullup resistor. The active-low, open-drain output is combined with a

debounced pushbutton input function. This pin can be activated by a pushbutton reset request. It has an

internal 50k nominal value pullup resistor to VCC. No external pullup resistors should be connected. If the

oscillator is disabled, tREC is bypassed and RST immediately goes high.

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

13 GND Ground

14 VBAT

Backup Power-Supply Input. When using the device with the VBAT input as the primary power source, this

pin should be decoupled using a 0.1μF to 1.0μF low-leakage capacitor. When using the device with the

VBAT input as the backup power source, the capacitor is not required. If VBAT is not used, connect to ground.

The device is UL recognized to ensure against reverse charging when used with a primary lithium battery.

Go to www.maxim-ic.com/qa/info/ul.

15 SDA

Serial Data Input/Output. This pin is the data input/output for the I2C serial interface. This open-drain pin

requires an external pullup resistor. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC.

16 SCL

Serial Clock Input. This pin is the clock input for the I2C serial interface and is used to synchronize data

movement on the serial interface. Up to 5.5V can be used for this pin, regardless of the voltage on VCC.

Detailed Description

The DS3231 is a serial RTC driven by a temperature-

compensated 32kHz crystal oscillator. The TCXO pro-

vides a stable and accurate reference clock, and

maintains the RTC to within ±2 minutes per year accu-

racy from -40°C to +85°C. The TCXO frequency output

is available at the 32kHz pin. The RTC is a low-power

clock/calendar with two programmable time-of-day

alarms and a programmable square-wave output. The

INT/SQW provides either an interrupt signal due to

alarm conditions or a square-wave output. The clock/cal-

endar 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 the 24-hour or 12-hour format

with an AM/PM indicator. The internal registers are

accessible though an I2C bus interface.

A temperature-compensated voltage reference and

comparator circuit monitors the level of VCC to detect

power failures and to automatically switch to the back-

up supply when necessary. The RST pin provides an

external pushbutton function and acts as an indicator

of a power-fail event.

Operation

The block diagram shows the main elements of the

DS3231. The eight blocks can be grouped into four

functional groups: TCXO, power control, pushbutton

function, and RTC. Their operations are described sep-

arately in the following sections.

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

32kHz TCXO

The temperature sensor, oscillator, and control logic

form the TCXO. The controller reads the output of the

on-chip temperature sensor and uses a lookup table to

determine the capacitance required, adds the aging

correction in AGE register, and then sets the capaci-

tance selection registers. New values, including

changes to the AGE register, are loaded only when a

change in the temperature value occurs, or when a

user-initiated temperature conversion is completed.

Temperature conversion occurs on initial application of

VCC and once every 64 seconds afterwards.

Power Control

This function is provided by a temperature-compensat-

ed voltage reference and a comparator circuit that

monitors the VCC level. When VCC is greater than VPF,

the part is powered by VCC. When VCC is less than VPF

but greater than VBAT, the DS3231 is powered by VCC.

If VCC is less than VPF and is less than VBAT, the

device is powered by VBAT. See Table 1.

To preserve the battery, the first time VBAT is applied to

the device, the oscillator will not start up until VCC

exceeds VPF, or until a valid I2C address is written to

the part. Typical oscillator startup time is less than one

second. Approximately 2 seconds after VCC is applied,

or a valid I2C address is written, the device makes a

temperature measurement and applies the calculated

correction to the oscillator. Once the oscillator is run-

ning, it continues to run as long as a valid power

source is available (VCC or VBAT), and the device con-

tinues to measure the temperature and correct the

oscillator frequency every 64 seconds.

On the first application of power (VCC) or when a valid

I2C address is written to the part (VBAT), the time and

date registers are reset to 01/01/00 01 00:00:00

(MM/DD/YY DOW HH:MM:SS).

VBAT Operation

There are several modes of operation that affect the

amount of VBAT current that is drawn. While the device

is powered by VBAT and the serial interface is active,

active battery current, IBATA, is drawn. When the serial

interface is inactive, timekeeping current (IBATT), which

includes the averaged temperature conversion current,

IBATTC, is used (refer to Application Note 3644:

Power

Considerations for Accurate Real-Time Clocks

for

details). Temperature conversion current, IBATTC, is

specified since the system must be able to support the

periodic higher current pulse and still maintain a valid

voltage level. Data retention current, IBATTDR, is the

current drawn by the part when the oscillator is

stopped (EOSC = 1). This mode can be used to mini-

mize battery requirements for times when maintaining

time and date information is not necessary, e.g., while

the end system is waiting to be shipped to a customer.

Pushbutton Reset Function

The DS3231 provides for a pushbutton switch to be

connected to the RST output pin. When the DS3231 is

not in a reset cycle, it continuously monitors the RST

signal for a low going edge. If an edge transition is

detected, the DS3231 debounces the switch by pulling

the RST low. After the internal timer has expired

(PBDB), the DS3231 continues to monitor the RST line.

If the line is still low, the DS3231 continuously monitors

the line looking for a rising edge. Upon detecting

release, the DS3231 forces the RST pin low and holds it

low for tRST.

RST is also used to indicate a power-fail condition.

When VCC is lower than VPF, an internal power-fail sig-

nal is generated, which forces the RST pin low. When

VCC returns to a level above VPF, the RST pin is held

low for approximately 250ms (tREC) to allow the power

supply to stabilize. If the oscillator is not running (see

the

Power Control

section) when VCC is applied, tREC is

bypassed and RST immediately goes high. Assertion of

the RST output, whether by pushbutton or power-fail

detection, does not affect the internal operation of the

DS3231.

Real-Time Clock

With the clock source from the TCXO, the RTC provides

seconds, minutes, hours, day, date, month, and year

information. The date at the end of the month is auto-

matically adjusted for months with fewer than 31 days,

including corrections for leap year. The clock operates

in either the 24-hour or 12-hour format with an AM/PM

indicator.

The clock provides two programmable time-of-day

alarms and a programmable square-wave output. The

INT/SQW pin either generates an interrupt due to alarm

condition or outputs a square-wave signal and the

selection is controlled by the bit INTCN.

SUPPLY CONDITION ACTIVE SUPPLY

VCC < VPF, VCC < VBAT V

BAT

VCC < VPF, VCC > VBAT V

VCC > VPF, VCC < VBAT V

VCC > VPF, VCC > VBAT V

Table 1. Power Control

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Figure 1. Timekeeping Registers

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

A D D R ESS BIT 7

MSB BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

LSB FUNCTION RANGE

00h 0 10 Seconds Seconds Seconds 00–59

01h 0 10 Minutes Minutes Minutes 00–59

AM/PM

02h 0 12/24

20 Hour 10 Hour Hour Hours 1–12 + AM/PM

00–23

03h 0 0 0 0 0 Day Day 1–7

04h 0 0 10 Date Date Date 01–31

05h Century 0 0 10 Month Month Month/

Century

01–12 +

Century

06h 10 Year Year Year 00–99

07h A1M1 10 Seconds Seconds Alarm 1 Seconds 00–59

08h A1M2 10 Minutes Minutes Alarm 1 Minutes 00–59

AM/PM

09h A1M3 12/24

20 Hour 10 Hour Hour Alarm 1 Hours 1–12 + AM/PM

00–23

Day Alarm 1 Day 1–7

0Ah A1M4 DY/DT 10 Date Date Alarm 1 Date 1–31

0Bh A2M2 10 Minutes Minutes Alarm 2 Minutes 00–59

AM/PM

0Ch A2M3 12/24

20 Hour 10 Hour Hour Alarm 2 Hours 1–12 + AM/PM

00–23

Day Alarm 2 Day 1–7

0Dh A2M4 DY/DT 10 Date Date Alarm 2 Date 1–31

0Eh EOSC BBSQW CONV RS2 RS1 INTCN A2IE A1IE Control —

0Fh OSF 0 0 0 EN32kHz BSY A2F A1F Control/Status —

10h SIGN DATA DATA DATA DATA DATA DATA DATA Aging Offset —

11h SIGN DATA DATA DATA DATA DATA DATA DATA MSB of Temp —

12h DATA DATA 0 0 0 0 0 0 LSB of Temp —

Address Map

Figure 1 shows the address map for the DS3231 time-

keeping registers. During a multibyte access, when the

address pointer reaches the end of the register space

(12h), it wraps around to location 00h. On an I2C

START or address pointer incrementing to location 00h,

the current time is transferred to a second set of regis-

ters. The time information is read from these secondary

registers, while the clock may continue to run. This

eliminates the need to reread the registers in case the

main registers update during a read.

I2C Interface

The I2C interface is accessible whenever either VCC or

VBAT is at a valid level. If a microcontroller connected

to the DS3231 resets because of a loss of VCC or other

event, it is possible that the microcontroller and

DS3231 I2C communications could become unsyn-

chronized, e.g., the microcontroller resets while read-

ing data from the DS3231. When the microcontroller

resets, the DS3231 I2C interface may be placed into a

known state by toggling SCL until SDA is observed to

be at a high level. At that point the microcontroller

should pull SDA low while SCL is high, generating a

START condition.

Clock and Calendar

The time and calendar information is obtained by read-

ing the appropriate register bytes. Figure 1 illustrates

the RTC registers. The time and calendar data are set

or initialized by writing the appropriate register bytes.

The contents of the time and calendar registers are in

DS3231

Maxim Integrated

the binary-coded decimal (BCD) format. The DS3231

can be run in either 12-hour or 24-hour mode. Bit 6 of

the hours register is defined as the 12- or 24-hour

mode select bit. When high, the 12-hour mode is

selected. In the 12-hour mode, bit 5 is the AM/PM bit

with logic-high being PM. In the 24-hour mode, bit 5 is

the 20-hour bit (20–23 hours). The century bit (bit 7 of

the month register) is toggled when the years register

overflows from 99 to 00.

The day-of-week register increments at midnight.

Values that correspond to the day of week are user-

defined but must be sequential (i.e., if 1 equals

Sunday, then 2 equals Monday, and so on). Illogical

time and date entries result in undefined operation.

When reading or writing the time and date registers, sec-

ondary (user) buffers are used to prevent errors when

the internal registers update. When reading the time and

date registers, the user buffers are synchronized to the

internal registers on any START and when the register

pointer rolls over to zero. The time information is read

from these secondary registers, while the clock contin-

ues to run. This eliminates the need to reread the regis-

ters in case the main registers update during a read.

The countdown chain is reset whenever the seconds regis-

ter is written. Write transfers occur on the acknowledge

from the DS3231. Once the countdown chain is reset, to

avoid rollover issues the remaining time and date registers

must be written within 1 second. The 1Hz square-wave out-

put, if enabled, transitions high 500ms after the seconds

data transfer, provided the oscillator is already running.

Alarms

The DS3231 contains two time-of-day/date alarms.

Alarm 1 can be set by writing to registers 07h to 0Ah.

Alarm 2 can be set by writing to registers 0Bh to 0Dh.

The alarms can be programmed (by the alarm enable

and INTCN bits of the control register) to activate the

INT/SQW output on an alarm match condition. Bit 7 of

each of the time-of-day/date alarm registers are mask

bits (Table 2). When all the mask bits for each alarm

are logic 0, an alarm only occurs when the values in the

timekeeping registers match the corresponding values

stored in the time-of-day/date alarm registers. The

alarms can also be programmed to repeat every sec-

ond, minute, hour, day, or date. Table 2 shows the pos-

sible settings. Configurations not listed in the table will

result in illogical operation.

The DY/DT bits (bit 6 of the alarm day/date registers)

control whether the alarm value stored in bits 0 to 5 of

that register reflects the day of the week or the date of

the month. If DY/DT is written to logic 0, the alarm will

be the result of a match with date of the month. If

DY/DT is written to logic 1, the alarm will be the result of

a match with day of the week.

When the RTC register values match alarm register set-

tings, the corresponding Alarm Flag ‘A1F’ or ‘A2F’ bit is

set to logic 1. If the corresponding Alarm Interrupt

Enable ‘A1IE’ or ‘A2IE’ is also set to logic 1 and the

INTCN bit is set to logic 1, the alarm condition will acti-

vate the INT/SQW signal. The match is tested on the

once-per-second update of the time and date registers.

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Table 2. Alarm Mask Bits

ALARM 1 REGISTER MASK BITS (BIT 7)

DY/DT

A1M4 A1M3 A1M2 A1M1 ALARM RATE

X 1 1 1 1 Alarm once per second

X 1 1 1 0 Alarm when seconds match

X 1 1 0 0 Alarm when minutes and seconds match

X 1 0 0 0 Alarm when hours, minutes, and seconds match

0 0 0 0 0 Alarm when date, hours, minutes, and seconds match

1 0 0 0 0 Alarm when day, hours, minutes, and seconds match

ALARM 2 REGISTER MASK BITS (BIT 7)

DY/DT

A2M4 A2M3 A2M2 ALARM RATE

X 1 1 1 Alarm once per minute (00 seconds of every minute)

X 1 1 0 Alarm when minutes match

X 1 0 0 Alarm when hours and minutes match

0 0 0 0 Alarm when date, hours, and minutes match

1 0 0 0 Alarm when day, hours, and minutes match

DS3231

Maxim Integrated

Special-Purpose Registers

The DS3231 has two additional registers (control and

status) that control the real-time clock, alarms, and

square-wave output.

Control Register (0Eh)

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 the DS3231 switches to VBAT. This

bit is clear (logic 0) when power is first applied. When

the DS3231 is powered by VCC, the oscillator is always

on regardless of the status of the EOSC bit. When

EOSC is disabled, all register data is static.

Bit 6: Battery-Backed Square-Wave Enable

(BBSQW). When set to logic 1 with INTCN = 0 and VCC

< VPF, this bit enables the square wave. When BBSQW

is logic 0, the INT/SQW pin goes high impedance when

VCC < VPF. This bit is disabled (logic 0) when power is

first applied.

Bit 5: Convert Temperature (CONV). Setting this bit to

1 forces the temperature sensor to convert the temper-

ature into digital code and execute the TCXO algorithm

to update the capacitance array to the oscillator. This

can only happen when a conversion is not already in

progress. The user should check the status bit BSY

before forcing the controller to start a new TCXO exe-

cution. A user-initiated temperature conversion does

not affect the internal 64-second update cycle.

A user-initiated temperature conversion does not affect

the BSY bit for approximately 2ms. The CONV bit

remains at a 1 from the time it is written until the conver-

sion is finished, at which time both CONV and BSY go

to 0. The CONV bit should be used when monitoring

the status of a user-initiated conversion.

Bits 4 and 3: Rate Select (RS2 and RS1). These bits

control the frequency of the square-wave output when

the square wave has been enabled. The following table

shows the square-wave frequencies that can be select-

ed with the RS bits. These bits are both set to logic 1

(8.192kHz) when power is first applied.

Bit 2: Interrupt Control (INTCN). This bit controls the

INT/SQW signal. When the INTCN bit is set to logic 0, a

square wave is output on the INT/SQW pin. When the

INTCN bit is set to logic 1, then a match between the

timekeeping registers and either of the alarm registers

activates the INT/SQW output (if the alarm is also

enabled). The corresponding alarm flag is always set

regardless of the state of the INTCN bit. The INTCN bit

is set to logic 1 when power is first applied.

Bit 1: Alarm 2 Interrupt Enable (A2IE). When set to

logic 1, this bit permits the alarm 2 flag (A2F) bit in the

status register to assert INT/SQW (when INTCN = 1).

When the A2IE bit is set to logic 0 or INTCN is set to

logic 0, the A2F bit does not initiate an interrupt signal.

The A2IE bit is disabled (logic 0) when power is first

applied.

Bit 0: Alarm 1 Interrupt Enable (A1IE). When set to

logic 1, this bit permits the alarm 1 flag (A1F) bit in the

status register to assert INT/SQW (when INTCN = 1).

When the A1IE bit is set to logic 0 or INTCN is set to

logic 0, the A1F bit does not initiate the INT/SQW sig-

nal. The A1IE bit is disabled (logic 0) when power is

first applied.

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

RS2 RS1 SQUARE-WAVE OUTPUT

FREQUENCY

0 0 1Hz

0 1 1.024kHz

1 0 4.096kHz

1 1 8.192kHz

SQUARE-WAVE OUTPUT FREQUENCY

Control Register (0Eh)

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

NAME: EOSC BBSQW CONV RS2 RS1 INTCN A2IE A1IE

POR: 0 0 0 1 1 1 0 0

DS3231

Maxim Integrated

Status Register (0Fh)

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 and may be used to judge the

validity of the timekeeping data. This bit is set to logic 1

any time that the oscillator stops. The following are exam-

ples of conditions that can cause the OSF bit to be set:

1) The first time power is applied.

2) The voltages present on both VCC and VBAT are

insufficient to support oscillation.

3) The EOSC bit is turned off in battery-backed mode.

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

age, etc.).

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

Bit 3: Enable 32kHz Output (EN32kHz). This bit con-

trols the status of the 32kHz pin. When set to logic 1, the

32kHz pin is enabled and outputs a 32.768kHz square-

wave signal. When set to logic 0, the 32kHz pin goes to

a high-impedance state. The initial power-up state of

this bit is logic 1, and a 32.768kHz square-wave signal

appears at the 32kHz pin after a power source is

applied to the DS3231 (if the oscillator is running).

Bit 2: Busy (BSY). This bit indicates the device is busy

executing TCXO functions. It goes to logic 1 when the

conversion signal to the temperature sensor is asserted

and then is cleared when the device is in the 1-minute

idle state.

Bit 1: Alarm 2 Flag (A2F). A logic 1 in the alarm 2 flag

bit indicates that the time matched the alarm 2 regis-

ters. If the A2IE bit is logic 1 and the INTCN bit is set to

logic 1, the INT/SQW pin is also asserted. A2F is

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

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

the value unchanged.

Bit 0: Alarm 1 Flag (A1F). A logic 1 in the alarm 1 flag

bit indicates that the time matched the alarm 1 regis-

ters. If the A1IE bit is logic 1 and the INTCN bit is set to

logic 1, the INT/SQW pin is also asserted. A1F is

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

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

the value unchanged.

Aging Offset

The aging offset register takes a user-provided value to

add to or subtract from the codes in the capacitance

array registers. The code is encoded in two’s comple-

ment, with bit 7 representing the sign bit. One LSB rep-

resents one small capacitor to be switched in or out of

the capacitance array at the crystal pins. The aging off-

set register capacitance value is added or subtracted

from the capacitance value that the device calculates

for each temperature compensation. The offset register

is added to the capacitance array during a normal tem-

perature conversion, if the temperature changes from

the previous conversion, or during a manual user con-

version (setting the CONV bit). To see the effects of the

aging register on the 32kHz output frequency immedi-

ately, a manual conversion should be started after each

aging register change.

Positive aging values add capacitance to the array,

slowing the oscillator frequency. Negative values

remove capacitance from the array, increasing the

oscillator frequency.

The change in ppm per LSB is different at different

temperatures. The frequency vs. temperature curve is

shifted by the values used in this register. At +25°C,

one LSB typically provides about 0.1ppm change in

frequency.

Use of the aging register is not needed to achieve the

accuracy as defined in the EC tables, but could be

used to help compensate for aging at a given tempera-

ture. See the

Typical Operating Characteristics

section

for a graph showing the effect of the register on accu-

racy over temperature.

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

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

NAME: Sign Data Data Data Data Data Data Data

POR: 0 0 0 0 0 0 0 0

Aging Offset (10h)

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

NAME: OSF 0 0 0 EN32kHz BSY A2F A1F

POR: 1 0 0 0 1 X X X

Status Register (0Fh)

DS3231

Maxim Integrated

Temperature Registers (11h–12h)

Temperature is represented as a 10-bit code with a res-

olution of 0.25°C and is accessible at location 11h and

12h. The temperature is encoded in two’s complement

format. The upper 8 bits, the integer portion, are at

location 11h and the lower 2 bits, the fractional portion,

are in the upper nibble at location 12h. For example,

00011001 01b = +25.25°C. Upon power reset, the reg-

isters are set to a default temperature of 0°C and the

controller starts a temperature conversion. The temper-

ature is read on initial application of VCC or I2C access

on VBAT and once every 64 seconds afterwards. The

temperature registers are updated after each user-initi-

ated conversion and on every 64-second conversion.

The temperature registers are read-only.

I2C Serial Data Bus

The DS3231 supports a bidirectional I2C bus and data

transmission protocol. A device that sends data onto

the bus is defined as a transmitter and a device receiv-

ing data is defined as a receiver. The device that con-

trols the message is called a master. The devices that

are controlled by the master are slaves. The bus must

be controlled by a master device that generates the

serial clock (SCL), controls the bus access, and gener-

ates the START and STOP conditions. The DS3231

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

bus are made through the SCL input and open-drain

SDA I/O lines. Within the bus specifications, a standard

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

(400kHz maximum clock rate) are defined. The DS3231

works in both modes.

The following bus protocol has been defined (Figure 2):

• Data transfer may be initiated only when the bus is

not busy.

• During data transfer, the data line must remain stable

whenever the clock line is high. Changes in the data

line while the clock line is high are interpreted as

control signals.

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 condition

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 information is transferred

byte-wise and each receiver acknowledges with a

ninth bit.

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, which is associ-

ated 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. Of

course, setup and hold times must be taken into

account. A master must signal an end of data to the

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Temperature Register (Upper Byte) (11h)

Temperature Register (Lower Byte) (12h)

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

NAME: Sign Data Data Data Data Data Data Data

POR: 0 0 0 0 0 0 0 0

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

NAME: Data Data 0 0 0 0 0 0

POR: 0 0 0 0 0 0 0 0

DS3231

Maxim Integrated

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 3 and 4 detail how data transfer is accom-

plished on the I2C bus. Depending upon 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 is transferred with the most

significant bit (MSB) first.

Data transfer from a slave transmitter to a master

receiver. The first byte (the slave address) is trans-

mitted by the master. The slave then returns an

acknowledge bit. Next follows a number of data

bytes transmitted by the slave to the master. The

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

SDA

SCL

IDLE

1–7 8 9 1–7 8 9 1–7 8 9

START

CONDITION STOP CONDITION

REPEATED START

SLAVE

ADDRESS

R/W ACK ACKDATA ACK/

NACK

DATA

MSB FIRST MSB LSB MSB LSB

REPEATED IF MORE BYTES

ARE TRANSFERRED

Figure 2. I2C Data Transfer Overview

...

AXXXXXXXXA1101000S 0 XXXXXXXX A XXXXXXXX A XXXXXXXX A P

<R/W> <WORD ADDRESS (n)> <DATA (n)> <DATA (n + 1)> <DATA (n + X)

S - START

A - ACKNOWLEDGE (ACK)

P - STOP

R/W - READ/WRITE OR DIRECTION BIT ADDRESS

DATA TRANSFERRED

(X + 1 BYTES + ACKNOWLEDGE)

MASTER TO SLAVESLAVE TO MASTER

<SLAVE

ADDRESS>

Figure 3. Data Write—Slave Receiver Mode

...

AXXXXXXXXA1101000S 1 XXXXXXXX A XXXXXXXX A XXXXXXXX A P

S - START

A - ACKNOWLEDGE (ACK)

P - STOP

A - NOT ACKNOWLEDGE (NACK)

R/W - READ/WRITE OR DIRECTION BIT ADDRESS

DATA TRANSFERRED

(X + 1 BYTES + ACKNOWLEDGE)

NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.

MASTER TO SLAVE SLAVE TO MASTER

<SLAVE

ADDRESS>

Figure 4. Data Read—Slave Transmitter Mode

DS3231

Maxim Integrated

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 all 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 condition

is also the beginning of the next serial transfer, the

bus will not be released. Data is transferred with the

most significant bit (MSB) first.

The DS3231 can operate in the following two modes:

Slave receiver mode (DS3231 write mode): Serial

data and clock are received through SDA and SCL.

After each byte is received, an acknowledge bit is

transmitted. START and STOP conditions are recog-

nized 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

master generates the START condition. The slave

address byte contains the 7-bit DS3231 address,

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

which is 0 for a write. After receiving and decoding

the slave address byte, the DS3231 outputs an

acknowledge on SDA. After the DS3231 acknowl-

edges the slave address + write bit, the master

transmits a word address to the DS3231. This sets

the register pointer on the DS3231, with the DS3231

acknowledging the transfer. The master may then

transmit zero or more bytes of data, with the DS3231

acknowledging each byte received. The register

pointer increments after each data byte is trans-

ferred. The master generates a STOP condition to

terminate the data write.

Slave transmitter mode (DS3231 read mode): The

first byte is received and handled as in the slave

receiver mode. However, in this mode, the direction

bit indicates that the transfer direction is reversed.

Serial data is transmitted on SDA by the DS3231

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 master generates a

START condition. The slave address byte contains

the 7-bit DS3231 address, which is 1101000, fol-

lowed by the direction bit (R/W), which is 1 for a

read. After receiving and decoding the slave

address byte, the DS3231 outputs an acknowledge

on SDA. The DS3231 then begins to transmit data

starting with the register address pointed to by the

before the initiation of a read mode, the first address

that is read is the last one stored in the register point-

er. The DS3231 must receive a not acknowledge to

end a read.

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

S - START

Sr - REPEATED START

A - ACKNOWLEDGE (ACK)

P - STOP

A - NOT ACKNOWLEDGE (NACK)

R/W - READ/WRITE OR DIRECTION BIT ADDRESS

<SLAVE

ADDRESS> <R/W>

AXXXXXXXXA1101000 1101000SSr0 A1

DATA TRANSFERRED

(X + 1 BYTES + ACKNOWLEDGE)

NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.

MASTER TO SLAVE SLAVE TO MASTER

AXXXXXXXX XXXXXXXX A XXXXXXXX A XXXXXXXX A P

...

Figure 5. Data Write/Read (Write Pointer, Then Read)—Slave Receive and Transmit

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Chip Information

SUBSTRATE CONNECTED TO GROUND

PROCESS: CMOS

Package Information

For the latest package outline information and land patterns,

go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-

” in the package code indicates RoHS status only. Package

drawings may show a different suffix character, but the draw-

ing pertains to the package regardless of RoHS status.

Pin Configuration

Handling, PC Board Layout,

and Assembly

The DS3231 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 N.C. (no connect) pins must be connect-

ed to ground.

Moisture-sensitive packages are shipped from the fac-

tory dry packed. Handling instructions listed on the

package label must be followed to prevent damage

during reflow. Refer to the IPC/JEDEC J-STD-020 stan-

dard for moisture-sensitive device (MSD) classifications

and reflow profiles. Exposure to reflow is limited to 2

times maximum.

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

16 SO W16#H2 21-0042 90-0107

DS3231

Maxim Integrated

32kHz SCL

SDA

VBAT

GND

N.C.

TOP VIEW

VCC

INT/SQW

N.C.

RST

N.C.

DS3231

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 1/05 Initial release. —

Changed Digital Temp Sensor Output from ±2°C to ±3°C. 1, 3

Updated Typical Operating Circuit. 1

Changed TA = -40°C to +85°C to TA = TMIN to TMAX. 2, 3, 4

1 2/05

Updated Block Diagram. 8

Added “UL Recognized” to Features; added lead-free packages and removed S from

top mark info in Ordering Information table; added ground connections to the N.C. pin

in the Typical Operating Circuit.

Added “noncondensing” to operating temperature range; changed VPF MIN from 2.35V

to 2.45V. 2

Added aging offset specification. 3

Relabeled TOC4. 7

Added arrow showing input on X1 in the Block Diagram. 8

Updated pin descriptions for VCC and VBAT. 9

Added the I2C Interface section. 10

Figure 1: Added sign bit to aging and temperature registers; added MSB and LSB. 11

Corrected title for rate select bits frequency table. 13

Added note that frequency stability over temperature spec is with aging offset register

= 00h; changed bit 7 from Data to Sign (Crystal Aging Offset Register). 14

Changed bit 7 from Data to Sign (Temperature Register); correct pin definitions in I2C

Serial Data Bus section. 15

2 6/05

Modified the Handing, PC Board Layout, and Assembly section to refer to

J-STD-020 for reflow profiles for lead-free and leaded packages. 17

3 11/05 Changed lead-free packages to RoHS-compliant packages. 1

Changed RST and UL bullets in Features. 1

Changed EC condition “VCC > VBAT” to “VCC = Active Supply (see Table 1).” 2, 3

Modified Note 12 to correct tREC operation. 6

Added various conditions text to TOCs 1, 2, and 3. 7

Added text to pin descriptions for 32kHz, VCC, and RST. 9

Table 1: Changed column heading “Powered By” to “Active Supply”; changed

“applied” to “exceeds VPF” in the Power Control section. 10

Indicated BBSQW applies to both SQW and interrupts; simplified temp convert

description (bit 5); added “output” to INT/SQW (bit 2). 13

4 10/06

Changed the Crystal Aging section to the Aging Offset section; changed “this bit

indicates” to “this bit controls” for the enable 32kHz output bit. 14

Added Warning note to EC table notes; updated Note 12. 6

Updated the Typical Operating Characteristics graphs. 7

In the Power Control section, added information about the POR state of the time and

date registers; in the Real-Time Clock section, added to the description of the RST

function.

5 4/08

In Figure 1, corrected the months date range for 04h from 00–31 to 01–31. 11

DS3231

Maxim Integrated

Extremely Accurate I2C-Integrated

RTC/TCXO/Crystal

Revision History (continued)

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

Updated the Typical Operating Circuit. 1

Removed the VPU parameter from the Recommended DC Operating Conditions table

and added verbiage about the pullup to the Pin Description table for INT/SQW, SDA,

and SCL.

2, 9

Added the Delta Time and Frequency vs. Temperature graph in the Typical Operating

Characteristics section. 7

Updated the Block Diagram. 8

Added the VBAT Operation section, improved some sections of text for the 32kHz

TCXO and Pushbutton Reset Function sections. 10

Added the register bit POR values to the register tables. 13, 14, 15

Updated the Aging Offset and Temperature Registers (11h–12h) sections. 14, 15

6 10/08

Updated the I2C timing diagrams (Figures 3, 4, and 5). 16, 17

7 3/10

Removed the “S” from the top mark in the Ordering Information table and the Pin

Configuration to match the packaging engineering marking specification. 1, 18

8 7/10

Updated the Typical Operating Circuit; removed the “Top Mark” column from the

Ordering Information; in the Absolute Maximum Ratings section, added the theta-JA

and theta-JC thermal resistances and Note 1, and changed the soldering temperature

to +260°C (lead(Pb)-free) and +240°C (leaded); updated the functional description of

the VBAT pin in the Pin Description; changed the timekeeping registers 02h, 09h, and

0Ch to “20 Hour” in Bit 5 of Figure 1; updated the BBSQW bit description in the Control

1, 2, 3, 4, 6,

9, 11, 12, 13,

DS3231

20 Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000

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. The parametric values (min and max limits) shown in the Electrical

Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.