MAXIM DS3231SN

19-5170; Rev 7; 3/10
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
Features
The DS3231 is a low-cost, extremely accurate I2C real-
♦ 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
time clock (RTC) with an integrated temperaturecompensated crystal oscillator (TCXO) and crystal. The
device incorporates a battery input, and maintains accurate timekeeping when main power to the device is interrupted. 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-ofday 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 reference 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 necessary. Additionally, the RST pin is monitored as a
pushbutton input for generating a µP reset.
Applications
Servers
Utility Power Meters
Telematics
GPS
Pin Configuration appears at end of data sheet.
Ordering Information
PART
TEMP RANGE
DS3231S#
PIN-PACKAGE
0°C to +70°C 16 SO
TOP
MARK
DS3231
DS3231SN# -40°C to +85°C 16 SO
DS3231N
#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 leadfree soldering processes. A "#" anywhere on the top mark
denotes a RoHS-compliant device.
Typical Operating Circuit
VCC
VCC
RPU = tR/CB
VCC
RPU
RPU
VCC
μP
SCL
SCL
INT/SQW
SDA
SDA
32kHz
RST
VBAT
RST
PUSHBUTTON
RESET
N.C.
DS3231
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
GND
N.C.
UL is a registered trademark of Underwriters Laboratories, Inc.
______________________________________________ Maxim Integrated Products
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.
1
DS3231
General Description
DS3231
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
ABSOLUTE MAXIMUM RATINGS
Voltage Range on VCC, VBAT, 32kHz, SCL, SDA, RST,
INT/SQW Relative to Ground.............................-0.3V to +6.0V
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/10s
Soldering Temperature....................................See the Handling,
PC Board Layout, and Assembly section.
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.
RECOMMENDED DC OPERATING CONDITIONS
(TA = TMIN to TMAX, unless otherwise noted.) (Notes 1, 2)
PARAMETER
MIN
TYP
MAX
UNITS
2.3
3.3
5.5
V
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
Supply Voltage
SYMBOL
CONDITIONS
VCC
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 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
VCC = 3.63V
200
VCC = 5.5V
300
Active Supply Current
ICCA
(Notes 3, 4)
110
ICCS
I2C bus inactive, 32kHz
output on, SQW output off
(Note 4)
VCC = 3.63V
Standby Supply Current
VCC = 5.5V
170
I2C bus inactive, 32kHz
output on, SQW output off
VCC = 3.63V
575
VCC = 5.5V
650
Temperature Conversion Current
ICCSCONV
Power-Fail Voltage
VPF
Logic 0 Output, 32kHz,
INT/SQW, SDA
VOL
Logic 0 Output, RST
Output Leakage Current 32kHz,
INT/SQW, SDA
μA
μA
V
I OL = 3mA
0.4
V
VOL
I OL = 1mA
0.4
V
ILO
Output high impedance
+1
μA
ILI
RST Pin I/O Leakage
I OL
VBAT Leakage Current
(VCC Active)
IBATLKG
2.45
RST high impedance (Note 5)
_____________________________________________________________________
-1
2.575
μA
2.70
Input Leakage SCL
2
UNITS
0
-1
+1
μA
-200
+10
μA
100
nA
25
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
(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 1, 2)
PARAMETER
Output Frequency
Frequency Stability vs.
Temperature (Commercial)
Frequency Stability vs.
Temperature (Industrial)
Frequency Stability vs. Voltage
SYMBOL
f OUT
f/f OUT
f/f OUT
CONDITIONS
MIN
VCC = 3.3V or VBAT = 3.3V
VCC = 3.3V or
VBAT = 3.3V,
aging offset = 00h
VCC = 3.3V or
VBAT = 3.3V,
aging offset = 00h
TYP
MAX
32.768
0°C to +40°C
kHz
±2
ppm
>40°C to +70°C
±3.5
-40°C to <0°C
±3.5
0°C to +40°C
±2
>40°C to +85°C
1
f/LSB
Specified at:
Temperature Accuracy
Temp
VCC = 3.3V or VBAT = 3.3V
Crystal Aging
f/f O
After reflow,
not production tested
ppm
±3.5
f/V
Trim Register Frequency
Sensitivity per LSB
UNITS
-40°C
0.7
+25°C
0.1
+70°C
0.4
+85°C
ppm/V
ppm
0.8
-3
+3
First year
±1.0
0–10 years
±5.0
°C
ppm
ELECTRICAL CHARACTERISTICS
(VCC = 0V, VBAT = 2.3V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETER
Active Battery Current
Timekeeping Battery Current
Temperature Conversion Current
Data-Retention Current
SYMBOL
CONDITIONS
MIN
IBATA
EOSC = 0, BBSQW = 0,
SCL = 400kHz (Note 4)
IBATT
EOSC = 0, BBSQW = 0,
VBAT = 3.63V
EN32kHz = 1,
SCL = SDA = 0V or
SCL = SDA = VBAT (Note 4) VBAT = 5.5V
IBATTC
IBATTDR
EOSC = 0, BBSQW = 0,
SCL = SDA = 0V or
SCL = SDA = VBAT
TYP
MAX
VBAT = 3.63V
70
VBAT = 5.5V
150
0.84
3.0
1.0
3.5
UNITS
μA
μA
VBAT = 3.63V
575
VBAT = 5.5V
650
μA
EOSC = 1, SCL = SDA = 0V, +25°C
100
nA
_____________________________________________________________________
3
DS3231
ELECTRICAL CHARACTERISTICS (continued)
DS3231
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 1)
PARAMETER
SYMBOL
SCL Clock Frequency
f SCL
Bus Free Time Between STOP
and START Conditions
tBUF
Hold Time (Repeated) START
Condition (Note 6)
tHD:STA
Low Period of SCL Clock
tLOW
High Period of SCL Clock
tHIGH
Data Hold Time (Notes 7, 8)
tHD:DAT
Data Setup Time (Note 9)
t SU:DAT
START Setup Time
t SU:STA
Rise Time of Both SDA and SCL
Signals (Note 10)
tR
Fall Time of Both SDA and SCL
Signals (Note 10)
tF
Setup Time for STOP Condition
t SU:STO
Capacitive Load for Each Bus
Line (Note 10)
CB
CONDITIONS
Fast mode
Standard mode
MIN
TYP
MAX
100
400
0
100
Fast mode
1.3
Standard mode
4.7
Fast mode
0.6
Standard mode
4.0
Fast mode
1.3
Standard mode
4.7
Fast mode
0.6
Standard mode
4.0
μs
μs
μs
0
0.9
Standard mode
0
0.9
100
Standard mode
250
Fast mode
0.6
Standard mode
4.7
Fast mode
Standard mode
Fast mode
Standard mode
μs
300
1000
300
20 +
0.1CB
0.6
Standard mode
4.7
μs
ns
20 +
0.1CB
Fast mode
kHz
μs
Fast mode
Fast mode
UNITS
300
ns
ns
μs
400
pF
Capacitance for SDA, SCL
CI/O
10
pF
Pulse Width of Spikes That Must
Be Suppressed by the Input Filter
t SP
30
ns
PBDB
250
ms
Pushbutton Debounce
Reset Active Time
tRST
Oscillator Stop Flag (OSF) Delay
t OSF
Temperature Conversion Time
(Note 11)
tCONV
250
ms
100
ms
125
200
ms
TYP
MAX
UNITS
POWER-SWITCH CHARACTERISTICS
(TA = TMIN to TMAX)
PARAMETER
SYMBOL
CONDITIONS
MIN
VCC Fall Time; VPF(MAX) to
VPF(MIN)
t VCCF
300
μs
VCC Rise Time; V PF(MIN) to
VPF(MAX)
t VCCR
0
μs
Recovery at Power-Up
4
tREC
(Note 12)
_____________________________________________________________________
250
300
ms
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
RST
PBDB
tRST
Power-Switch Timing
VCC
VPF(MAX)
VPF
VPF
VPF(MIN)
tVCCF
tVCCR
tREC
RST
_____________________________________________________________________
5
DS3231
Pushbutton Reset Timing
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
DS3231
Data Transfer on I2C Serial Bus
SDA
tBUF
tF
tHD:STA
tLOW
tSP
SCL
tHIGH
tHD:STA
tHD:DAT
STOP
tSU:STA
tR
START
tSU:STO
tSU:DAT
REPEATED
START
NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN).
WARNING: Negative undershoots below -0.3V while the part is in battery-backed mode may cause loss of data.
Limits at -40°C are guaranteed by design and not production tested.
All voltages are referenced to ground.
ICCA—SCL clocking at max frequency = 400kHz.
Current is the averaged input current, which includes the temperature conversion current.
The RST pin has an internal 50kΩ (nominal) pullup resistor to VCC.
After this period, the first clock pulse is generated.
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 8: The maximum tHD:DAT needs only to be met if the device does not stretch the low period (tLOW) of the SCL signal.
Note 9: 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 10: CB—total capacitance of one bus line in pF.
Note 11: 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 12: This delay applies only if the oscillator is enabled and running. If the EOSC bit is a 1, tREC is bypassed and RST immediately goes high. The state of RST does not affect the I2C interface, RTC, or TCXO.
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
6
_____________________________________________________________________
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
BSY = 0, SCL = SDA = VCC
125
1.2
DS3231 toc01
1.1
RST ACTIVE
1.0
IBAT (μA)
75
EN32kHz = 0
50
0.8
25
0.7
0
0.6
3.0
3.5
4.0
4.5
5.5
5.0
2.3
3.3
4.3
5.3
VCC (V)
VBAT (V)
SUPPLY CURRENT
vs. TEMPERATURE
FREQUENCY DEVIATION
vs. TEMPERATURE vs. AGING VALUE
VCC = 0, EN32kHz = 1, BSY = 0,
SDA = SCL = VBAT OR GND
60
50
FREQUENCY DEVIATION (ppm)
1.0
2.5
DS3231 toc03
2.0
0.9
0.8
0.7
8
40
-33
30
20
0
10
0
-10
32
-20
127
-30
0.6
-40
-40
-15
10
35
60
85
-15
-40
10
TEMPERATURE (°C)
35
60
85
TEMPERATURE (°C)
DELTA TIME AND FREQUENCY
vs. TEMPERATURE
DS3231 toc05
20
0
-20
DELTA FREQUENCY (ppm)
IBAT (μA)
EN32kHz = 1
0.9
DS3231 toc04
ICCS (μA)
100
VCC = 0V, BSY = 0,
SDA = SCL = VBAT OR VCC
-40
-60
-80
0
CRYSTAL
+20ppm
-20
TYPICAL CRYSTAL,
UNCOMPENSATED
-100
-120
-140
CRYSTAL
-20ppm
DS3231
ACCURACY
BAND
-40
-60
DELTA TIME (MIN/YEAR)
150
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
DS3231 toc02
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
-80
-160
-180
-200
-100
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80
TEMPERATURE (°C)
_____________________________________________________________________
7
DS3231
Typical Operating Characteristics
(VCC = +3.3V, TA = +25°C, unless otherwise noted.)
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
DS3231
Block Diagram
32kHz
X1
OSCILLATOR AND
CAPACITOR ARRAY
N
CONTROL LOGIC/
DIVIDER
X2
SQUARE-WAVE BUFFER;
INT/SQW CONTROL
1Hz
VCC
VBAT
N
TEMPERATURE
SENSOR
POWER CONTROL
GND
INT/SQW
ALARM, STATUS, AND
CONTROL REGISTERS
1Hz
CLOCK AND CALENDAR
REGISTERS
SCL
SDA
I2C INTERFACE AND
ADDRESS REGISTER
DECODE
USER BUFFER
(7 BYTES)
DS3231
8
VOLTAGE REFERENCE;
DEBOUNCE CIRCUIT;
PUSHBUTTON RESET
_____________________________________________________________________
VCC
RST
N
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
PIN
NAME
1
32kHz
2
VCC
FUNCTION
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.
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.
INT/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.
RST
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. This pin should be decoupled using a 0.1μF to 1.0μF low-leakage capacitor.
If the I2C interface is inactive whenever the device is powered by the VBAT input, the decoupling capacitor
is not required. If VBAT is not used, connect to ground. UL recognized to ensure against reverse charging
when used with a 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.
3
4
Detailed Description
The DS3231 is a serial RTC driven by a temperaturecompensated 32kHz crystal oscillator. The TCXO provides a stable and accurate reference clock, and
maintains the RTC to within ±2 minutes per year accuracy 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/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 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 backup 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 separately in the following sections.
_____________________________________________________________________
9
DS3231
Pin Description
DS3231
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 capacitance 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-compensated 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 V CC is less than V PF and is less than V BAT , the
device is powered by VBAT. See Table 1.
Table 1. Power Control
SUPPLY CONDITION
ACTIVE SUPPLY
VCC < V PF, VCC < VBAT
VBAT
VCC < V PF, VCC > VBAT
VCC
VCC > V PF, VCC < VBAT
VCC
VCC > V PF, VCC > VBAT
VCC
To preserve the battery, the first time VBAT is applied to
the device, the oscillator will not start up until V CC
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 running, it continues to run as long as a valid power
source is available (VCC or VBAT), and the device continues 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,
10
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 minimize 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 signal 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 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 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.
____________________________________________________________________
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
ADDRESS
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
02h
0
12/24
Hour
Hours
1–12 + AM/PM
00–23
03h
0
0
Day
1–7
04h
0
0
05h
Century
AM/PM
0
0
0
Day
10 Date
0
06h
10 Hour
10 Hour
0
10 Month
Date
Date
01–31
Month
Month/
Century
01–12 +
Century
Year
Year
00–99
07h
A1M1
10 Year
10 Seconds
Seconds
Alarm 1 Seconds
00–59
08h
A1M2
10 Minutes
Minutes
Alarm 1 Minutes
00–59
09h
A1M3
12/24
Hour
Alarm 1 Hours
1–12 + AM/PM
00–23
0Ah
A1M4
DY/DT
Day
Alarm 1 Day
1–7
0Bh
A2M2
0Ch
A2M3
12/24
0Dh
A2M4
DY/DT
0Eh
EOSC
BBSQW
CONV
RS2
RS1
INTCN
A2IE
A1IE
0Fh
OSF
0
0
0
EN32kHz
BSY
A2F
A1F
AM/PM
10 Hour
10 Hour
10 Date
10 Minutes
AM/PM
10 Hour
Date
Alarm 1 Date
1–31
Minutes
Alarm 2 Minutes
00–59
Hour
Alarm 2 Hours
1–12 + AM/PM
00–23
Day
Alarm 2 Day
1–7
Alarm 2 Date
1–31
Control
—
Control/Status
—
10 Hour
10 Date
Date
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
—
Note: Unless otherwise specified, the registers’ state is not defined when power is first applied.
Address Map
Figure 1 shows the address map for the DS3231 timekeeping 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 I 2 C
START or address pointer incrementing to location 00h,
the current time is transferred to a second set of registers. 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 I 2C communications could become unsynchronized, e.g., the microcontroller resets while reading 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 reading 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
____________________________________________________________________
11
DS3231
Figure 1. Timekeeping Registers
DS3231
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
Alarms
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 second 10-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 userdefined 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, secondary (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 continues to run. This eliminates the need to reread the registers in case the main registers update during a read.
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 second, minute, hour, day, or date. Table 2 shows the possible 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 settings, 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 activate the INT/SQW signal. The match is tested on the
once-per-second update of the time and date registers.
The countdown chain is reset whenever the seconds register 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 output, if enabled, transitions high 500ms after the seconds
data transfer, provided the oscillator is already running.
Table 2. Alarm Mask Bits
DY/DT
ALARM RATE
A1M4
A1M3
A1M2
A1M1
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
DY/DT
12
ALARM 1 REGISTER MASK BITS (BIT 7)
ALARM 2 REGISTER MASK BITS (BIT 7)
A2M4
A2M3
ALARM RATE
A2M2
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
____________________________________________________________________
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
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
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 oscillator 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 and the DS3231 is being
powered by the VBAT pin, this bit enables the squarewave or interrupt output when VCC is absent. When
BBSQW is logic 0, the INT/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 5: Convert Temperature (CONV). Setting this bit to
1 forces the temperature sensor to convert the temperature 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 execution. 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 conversion 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
SQUARE-WAVE OUTPUT FREQUENCY
SQUARE-WAVE OUTPUT
FREQUENCY
RS2
RS1
0
0
1Hz
0
1
1.024kHz
1
0
4.096kHz
1
1
8.192kHz
the square wave has been enabled. The following table
shows the square-wave frequencies that can be selected 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 signal. The A1IE bit is disabled (logic 0) when power is
first applied.
____________________________________________________________________
13
DS3231
Control Register (0Eh)
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
DS3231
Status Register (0Fh)
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)
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.
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 examples 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.
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 complement, with bit 7 representing the sign bit. One LSB represents one small capacitor to be switched in or out of
the capacitance array at the crystal pins. The aging offset 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 temperature conversion, if the temperature changes from
the previous conversion, or during a manual user conversion (setting the CONV bit). To see the effects of the
aging register on the 32kHz output frequency immediately, a manual conversion should be started after each
aging register change.
4) External influences on the crystal (i.e., noise, leakage, etc.).
This bit remains at logic 1 until written to logic 0.
Bit 3: Enable 32kHz Output (EN32kHz). This bit controls the status of the 32kHz pin. When set to logic 1, the
32kHz pin is enabled and outputs a 32.768kHz squarewave 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).
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.
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 registers. 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-
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 temperature. See the Typical Operating Characteristics section
for a graph showing the effect of the register on accuracy over temperature.
Aging Offset (10h)
14
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
____________________________________________________________________
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
Temperature Register (Lower Byte) (12h)
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
Temperature Registers (11h–12h)
Temperature is represented as a 10-bit code with a resolution 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 registers are set to a default temperature of 0°C and the
controller starts a temperature conversion. The temperature 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-initiated 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 receiving data is defined as a receiver. The device that controls 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 generates 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 associated 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
____________________________________________________________________
15
DS3231
Temperature Register (Upper Byte) (11h)
DS3231
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
MSB FIRST
MSB
LSB
MSB
LSB
SDA
SLAVE
ADDRESS
SCL
R/W
1–7
IDLE
8
ACK
DATA
9
1–7
START
CONDITION
ACK
8
9
DATA
1–7
ACK/
NACK
8
9
REPEATED IF MORE BYTES
ARE TRANSFERRED
STOP CONDITION
REPEATED START
Figure 2. I2C Data Transfer Overview
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.
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 transmitted 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
Figures 3 and 4 detail how data transfer is accomplished on the I2C bus. Depending upon the state of
the R/W bit, 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
<SLAVE
ADDRESS>
S
1101000
<R/W>
0
A
<WORD ADDRESS (n)>
XXXXXXXX
<DATA (n)>
A
S - START
SLAVE TO MASTER
A - ACKNOWLEDGE (ACK)
P - STOP
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
<DATA (n + 1)>
XXXXXXXX
A
XXXXXXXX
<DATA (n + X)
A
...
XXXXXXXX
A
P
A
P
MASTER TO SLAVE
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
Figure 3. Data Write—Slave Receiver Mode
<SLAVE
ADDRESS>
S
1101000
<R/W>
<DATA (n)>
1
XXXXXXXX
A
S - START
MASTER TO SLAVE
A - ACKNOWLEDGE (ACK)
P - STOP
A - NOT ACKNOWLEDGE (NACK)
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
<DATA (n + 1)>
A
<DATA (n + 2)>
XXXXXXXX
A
XXXXXXXX
...
XXXXXXXX
SLAVE TO MASTER
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.
Figure 4. Data Read—Slave Transmitter Mode
16
<DATA (n + X)>
A
____________________________________________________________________
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
S
1101000
0
<DATA (n)>
XXXXXXXX
<WORD ADDRESS (n)>
A
XXXXXXXX
A
XXXXXXXX
<SLAVE ADDRESS (n)> <R/W>
A
<DATA (n + 1)>
DS3231
<SLAVE
ADDRESS> <R/W>
Sr
1101000
1
<DATA (n + 2)>
A
S - START
MASTER TO SLAVE
Sr - REPEATED START
A - ACKNOWLEDGE (ACK)
P - STOP
A - NOT ACKNOWLEDGE (NACK)
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
XXXXXXXX
A
<DATA (n + X)>
A
...
XXXXXXXX
A
P
SLAVE TO MASTER
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.
Figure 5. Data Write/Read (Write Pointer, Then Read)—Slave Receive and Transmit
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 pulses 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 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 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 acknowledges 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 transferred. 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, followed 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
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 DS3231 must receive a not acknowledge to
end a read.
____________________________________________________________________
17
DS3231
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
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 connected to ground.
Moisture-sensitive packages are shipped from the factory 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 standard for moisture-sensitive device (MSD) classifications
and reflow profiles. Exposure to reflow is limited to 2
times maximum.
Pin Configuration
Chip Information
TRANSISTOR COUNT: 33,000
SUBSTRATE CONNECTED TO GROUND
TOP VIEW
PROCESS: CMOS
32kHz 1
16 SCL
VCC 2
15 SDA
INT/SQW 3
14 VBAT
RST 4
13 GND
N.C. 5
DS3231
N.C. 6
Theta-JA: +73°C/W
Theta-JC: +23°C/W
12 N.C.
Package Information
11 N.C.
N.C. 7
10 N.C.
N.C. 8
9
SO
18
Thermal Information
N.C.
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 drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
16 SO
W16#H2
21-0042
____________________________________________________________________
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
REVISION
NUMBER
REVISION
DATE
0
1/05
DESCRIPTION
Initial release.
—
Changed Digital Temp Sensor Output from ±2°C to ±3°C.
1
2
2/05
6/05
Updated Typical Operating Circuit.
Changed TA = -40°C to +85°C to TA = TMIN to TMAX.
11/05
5
10/06
4/08
1
2, 3, 4
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.
1
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
15
17
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).”
Modified Note 12 to correct tREC operation.
4
1, 3
Updated Block Diagram.
Changed bit 7 from Data to Sign (Temperature Register); correct pin definitions in
I2C Serial Data Bus section.
Modified the Handing, PC Board Layout, and Assembly section to refer to
J-STD-020 for reflow profiles for lead-free and leaded packages.
3
PAGES
CHANGED
2, 3
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
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.
10
In Figure 1, corrected the months date range for 04h from 00–31 to 01–31.
11
____________________________________________________________________
19
DS3231
Revision History
DS3231
Extremely Accurate I2C-Integrated
RTC/TCXO/Crystal
Revision History (continued)
REVISION
NUMBER
REVISION
DATE
DESCRIPTION
Updated the Typical Operating Circuit.
1
Removed the V PU 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.
6
10/08
3/10
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.
7
PAGES
CHANGED
13, 14, 15
Updated the Aging Offset and Temperature Registers (11h–12h) sections.
14, 15
Updated the I2C timing diagrams (Figures 3, 4, and 5).
16, 17
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
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implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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