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.
±5ppm, I2C Real-Time Clock
19-5312; Rev 3; 12/11
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an automotive qualified part.
Typical Operating Circuit
General Description
The DS3231M is a low-cost, extremely accurate, I2C
real-time clock (RTC). The device incorporates a battery
input and maintains accurate timekeeping when main
power to the device is interrupted. The integration of
the microelectromechanical systems (MEMS) resona-
tor enhances the long-term accuracy of the device and
reduces the piece-part count in a manufacturing line.
The DS3231M is available in the same footprint as the
popular DS3231 RTC.
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 1Hz 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 microprocessor reset.
See the Block Diagram for more details.
Applications
Power Meters
Industrial Applications
Ordering Information
Features
S Timekeeping_Accuracy_Q5ppm_(Q0.432_Second/
Day)_from_-40NC_to_+85NC
S Battery_Backup_for_Continuous_Timekeeping
S Low_Power_Consumption
S Footprint_and_Functionally_Compatible_to_DS3231
S Complete_Clock_Calendar_Functionality_Including_
Seconds,_Minutes,_Hours,_Day,_Date,_Month,_and_
Year_with_Leap_Year_Compensation_Up_to_Year_
2100
S Two_Time-of-Day_Alarms
S 1Hz_and_32.768kHz_Outputs
S Reset_Output_and_Pushbutton_Input_with_
Debounce
S Fast_(400kHz)_I2C-Compatible_Serial_Bus
S +2.3V_to_+5.5V_Supply_Voltage
S Digital_Temp_Sensor_with_Q3NC_Accuracy
S -40NC_to_+85NC_Temperature_Range
S 8-Pin_or_16-Pin_SO_Packages
S Underwriters_Laboratories_(UL)_Recognized
DS3231M
SCL
SDA
32KHZ VBAT
INT/SQW
RST
+3.3V+3.3V
CPU
I/O PORT
INTERRUPTS
PART TEMP_RANGE PIN-PACKAGE
DS3231MZ+ -40NC to +85NC8 SO
DS3231MZ/V+ -40NC to +85NC8 SO
DS3231M+ -40NC to +85NC16 SO
DS3231M
±5ppm, I2C Real-Time Clock
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 Any Pin Relative to GND ........-0.3V to +6.0V
Operating Temperature Range .......................... -40NC to +85NC
Storage Temperature Range ............................ -55NC to +125NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
RECOMMENDED_OPERATING_CONDITIONS
(TA = -40NC to +85NC, unless otherwise noted.) (Note 1)
ELECTRICAL_CHARACTERISTICS—FREQUENCY_AND_TIMEKEEPING
(VCC or VBAT = +3.3V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and
TA = +25NC, unless otherwise noted.)
DC_ELECTRICAL_CHARACTERISTICS—GENERAL
(VCC = +2.3V to +5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and TA =
+25NC, unless otherwise noted.)
ABSOLUTE_MAXIMUM_RATINGS
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VCC 2.3 3.3 5.5 V
VBAT 2.3 3.0 5.5
Logic 1 VIH 0.7 x
VCC
VCC +
0.3 V
Logic 0 VIL -0.3 0.3 x
VCC V
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
1Hz Frequency Tolerance Df/fOUT Measured over R 10s interval Q5ppm
1Hz Frequency Stability vs. VCC
Voltage Df/V Q1ppm/V
Timekeeping Accuracy tKAQ0.432 Seconds/
Day
32kHz Frequency Tolerance Df/fOUT Q2.5 %
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Active Supply Current
(I2C Active: Includes
Temperature Conversion Current)
ICCA
VCC = +3.63V 200
µA
VCC = VCCMAX 300
Standby Supply Current
(I2C Inactive: Includes
Temperature Conversion Current)
ICCS
VCC = +3.63V 130
µA
VCC = VCCMAX 200
Temperature Conversion Current
(I2C Inactive) ICCSCONV VCC = +3.63V 575 µA
VCC = VCCMAX 650
DS3231M
2
Maxim Integrated
±5ppm, I2C Real-Time Clock
AC_ELECTRICAL_CHARACTERISTICS—POWER_SWITCH
(TA = -40NC to +85NC, unless otherwise noted.) (Figure 2)
DC_ELECTRICAL_CHARACTERISTICS—GENERAL_(continued)
(VCC = +2.3V to +5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and TA =
+25NC, unless otherwise noted.)
DC_ELECTRICAL_CHARACTERISTICS—VBAT_CURRENT_CONSUMPTION
(VCC = 0V, VBAT = +2.3V to +5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VCC = 0V, VBAT = +3.0V,
and TA = +25NC, unless otherwise noted.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Power-Fail Voltage VPF 2.45 2.575 2.70 V
Logic 0 Output
(32KHZ, INT/SQW, SDA) VOL IOL = 3mA 0.4 V
Logic 0 Output
(RST)VOL IOL = 1mA 0.4 V
Output Leakage
(32KHZ, INT/SQW, SDA) ILO -0.1 +0.1 µA
Input Leakage
(SCL) ILI -0.1 +0.1 µA
RST I/O Leakage IOL -200 +10 µA
VBAT Leakage IBATLKG 25 100 nA
Temperature Accuracy TEMPACC VCC or VBAT = +3.3V Q3NC
Temperature Conversion Time tCONV 10 ms
Pushbutton Debounce PBDB 250 ms
Reset Active Time tRST 250 ms
Oscillator Stop Flag (OSF) Delay tOSF (Note 2) 125 200 ms
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Active Battery Current
(I2C Active) (Note 3) IBATA VBAT = +3.63V 70 µA
VBAT = VBATMAX 150
Timekeeping Battery Current
(I2C Inactive) (Note 3) IBATT VBAT = +3.63V, EN32KHZ = 0 2 3.0 µA
VBAT = VBATMAX, EN32KHZ = 0 2 3.5
Temperature Conversion Current
(I2C Inactive) IBATTC VBAT = +3.63V 575 µA
VBAT = VBATMAX 650
Data Retention Current
(Oscillator Stopped and I2C
Inactive)
IBATDR TA = +25NC100 nA
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
VCC Fall Time, VPFMAX to
VPFMIN tVCCF 300 Fs
VCC Rise Time, VPFMIN to
VPFMAX tVCCR 0Fs
Recovery at Power-Up tREC (Note 4) 250 300 ms
DS3231M
Maxim Integrated
3
±5ppm, I2C Real-Time Clock
AC_ELECTRICAL_CHARACTERISTICS—I2C_INTERFACE
(VCC or VBAT = +2.3V to +5.5V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V,
and TA = +25NC, unless otherwise noted.) (Note 5, Figure 1)
Note_1:_All voltages are referenced to ground.
Note_2:_The parameter tOSF is the period of time the oscillator must be stopped for the OSF flag to be set.
Note_3: Includes the temperature conversion current (averaged).
Note_4: This delay applies only if the oscillator is enabled. If the EOSC bit is 1, tREC is bypassed and RST immediately goes high.
The state of RST does not affect the I2C interface or RTC functions.
Note_5:__Interface timing shown is for fast-mode (400kHz) operation. This device is also backward-compatible with standard mode
I2C timing.
Note_6:_CB: Total capacitance of one bus line in picofarads.
Note_7:_Guaranteed by design; not 100% production tested.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL Clock Frequency fSCL 0 400 kHz
Bus Free Time Between STOP
and START Conditions tBUF 1.3 Fs
Hold Time (Repeated) START
Condition tHD:STA 0.6 Fs
Low Period of SCL tLOW 1.3 Fs
High Period of SCL tHIGH 0.6 Fs
Data Hold Time tHD:DAT 0 0.9 Fs
Data Set-Up Time tSU:DAT 100 ns
START Set-Up Time tSU:STA 0.6 Fs
SDA and SCL Rise Time tR(Note 6) 20 +
0.1CB300 ns
SDA and SCL Fall Time tF(Note 6) 20 +
0.1CB300 ns
STOP Set-Up Time tSU:STO 0.6 Fs
SDA, SCL Input Capacitance CBIN (Note 7) 10 pF
DS3231M
4
Maxim Integrated
±5ppm, I2C Real-Time Clock
Timing Diagrams
Figure 3. Pushbutton Reset Timing
Figure 1. I2C Timing
Figure 2. Power Switch Timing
SCL
NOTE: TIMING IS REFERENCED TO VILMAX AND VIHMIN.
SDA
STOP START REPEATED
START
tBUF
tHD:STA
tHD:DAT tSU:DAT
tSU:STO
tHD:STA
tSP
tSU:STA
tHIGH
tR
tF
tLOW
tRST
PBDB
RST
tVCCF tVCCR
tREC
VPFMAX
VCC
RST
VPFMIN
DS3231M
Maxim Integrated
5
±5ppm, I2C Real-Time Clock
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
FREQUENCY ERROR
vs. TEMPERATURE
DS3231M toc06
TEMPERATURE (°C)
FREQUENCY ERROR (ppm)
500
-8
-6
-4
-2
0
2
4
6
8
10
-10
-50 100
LIMITS
VCC = 3.3V
RST OUTPUT VOLTAGE
vs. POWER SUPPLY VOLTAGE
DS3231M toc05
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
42
1
2
3
4
5
6
0
0 6
VBAT = 3.0V,
TA = +25°C
TRACKS WITH VCC
RST OUTPUT VOLTAGE
vs. OUTPUT CURRENT
DS3231M toc04
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
4321
0.1
0.2
0.3
0.4
0.5
0
0 5
VCC = 2.45V,
VBAT = 3.0V,
TA = +25°C
INT/SQW OUTPUT VOLTAGE
vs. OUTPUT CURRENT
DS3231M toc03
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
8642
0.1
0.2
0.3
0.4
0.5
0
0 10
VCC = 2.3V,
VBAT = 0V,
TA = +25°C
BATTERY-SUPPLY CURRENT
vs. BATTERY-SUPPLY VOLTAGE
DS3231M toc02
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
543
1.5
2.0
2.5
3.0
3.5
4.0
1.0
2 6
VCC = 0V, EN32KHZ = 1, BBSQW = 0
+85°C
+25°C
-40°C
POWER-SUPPLY CURRENT
vs. POWER-SUPPLY VOLTAGE
DS3231M toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
543
60
70
80
90
100
110
120
130
140
150
50
2 6
VBAT = 2.3V, EN32KHZ = 1, IOUT = 0mA
INCREASE BELOW VPF
DUE TO INTERNAL PULLUP
RESISTOR ON RST
+85°C
+25°C
-40°C
POWER-SUPPLY CURRENT
vs. SCL FREQUENCY
DS3231M toc07
SCL FREQUENCY (kHz)
SUPPLY CURRENT (µA)
300200100
90
100
110
120
130
140
150
160
170
180
190
200
80
0 400
TA = +25°C
+5.5V
+2.7V
+3.5V
DS3231M
6
Maxim Integrated
±5ppm, I2C Real-Time Clock
Pin Configuration
Pin Description
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
32KHZ SCL
SDA
VBAT
GND
N.C.
N.C.
N.C.
N.C.
TOP VIEW
SO
VCC
INT/SQW
N.C.
RST
N.C.
N.C.
N.C.
DS3231M
DS3231M
+
VBAT
GNDRST
1
2
8
7
SCL
SDAVCC
INT/SQW
32KHZ
SO
TOP VIEW
3
4
6
5
+
PIN NAME FUNCTION
8_SO 16_SO
1 1 32KHZ
32.768kHz Output (50% Duty Cycle). This open-drain pin requires an external pullup resistor.
When enabled with the EN32KHZ bit in the Status register (0Fh), this output operates on either
power supply. This pin can be left open circuit if not used.
2 2 VCC DC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1FF to 1.0FF
capacitor. Connect to ground if not used.
3 3 INT/
SQW
Active-Low Interrupt or 1Hz Square-Wave Output. This open-drain pin requires an external pullup
resistor connected to a supply at 5.5V or less. It can be left open if not used. 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 1Hz square wave. When INTCN is set to logic 1, 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.
4 4 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 50kI (RPU) 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. These pins must be connected to ground.
5 13 GND Ground
6 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 0.1FF to 1.0FF 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 for more information.
DS3231M
Maxim Integrated
7
±5ppm, I2C Real-Time Clock
Detailed Description
The DS3231M is a serial real-time clock (RTC) driven by
an internal, temperature-compensated, microelectrome-
chanical systems (MEMS) resonator. The oscillator pro-
vides a stable and accurate reference clock and main-
tains the RTC to within Q0.432 seconds-per-day accu-
racy from -40NC to +85NC. The RTC is a low-power clock/
calendar with two programmable time-of-day alarms. INT/
SQW provides either an interrupt signal due to alarm
conditions or a 1Hz square wave. 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-compensat-
ed 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 device’s main elements.
Each of the major blocks is described separately in the
following sections.
Block Diagram
Pin Description (continued)
DS3231M
N
N
TIME-BASE
RESONATOR
TEMP
SENSOR
INTERRUPT
OR 1Hz
SELECT
DIVIDER
INT/SQW
1Hz
DIGITAL
ADJUSTMENT
FACTORY TRIM
N
32KHZ
SDA
GND
SCL
VBAT
VCC
RST
RPU
CLOCK/CALENDAR
WITH ALARM
CONTROL AND STATUS
REGISTERS
I2C
INTERFACE
POWER
CONTROL
PIN NAME FUNCTION
8_SO 16_SO
7 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 volt-
age on VCC.
8 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. The pullup voltage can be up to 5.5V, regardless of the
voltage on VCC.
DS3231M
8
Maxim Integrated
±5ppm, I2C Real-Time Clock
High-Accuracy Time Base
The temperature sensor, oscillator, and digital adjust-
ment controller logic form the highly accurate time base.
The controller reads the output of the on-board tempera-
ture sensor and adjusts the final 1Hz output to maintain
the required accuracy. The device is trimmed at the
factory to maintain a tight accuracy over the operating
temperature range. When the device is powered by VCC,
the adjustment occurs once a second. When the device
is powered by VBAT, the adjustment occurs once every
10s to conserve power. Adjusting the 1Hz time base less
often does not affect the device’s long-term timekeeping
accuracy. The device also contains an Aging Offset reg-
ister that allows a constant offset (positive or negative) to
be added to the factory-trimmed adjustment value.
Power-Supply Configurations
The DS3231M can be configured to operate on a single
power supply (using either VCC or VBAT) or in a dual-
supply configuration, which provides a backup supply
source to keep the timekeeping circuits alive during
absence of primary system power.
Figure 4 illustrates a single-supply configuration using
VCC only, with the VBAT input grounded. When VCC < VPF,
the RST output is asserted (active low). Temperature
conversions are executed once per second.
Figure 5 illustrates a single-supply configuration using
VBAT only, with the VCC input grounded. The RST output
is disabled and is held at ground through the connection
of the internal pullup resistor. Temperature conversions
are executed once every 10s.
Figure 6 illustrates a dual-supply configuration, using
the VCC supply for normal system operation and the
VBAT supply for backup power. In this configuration, the
power-selection 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 device is powered by VCC. When VCC is less
than VPF but greater than VBAT, the device is powered
Figure 4. Single Supply (VCC Only)
Figure 5. Single Supply (VBAT Only)
Figure 6. Dual Power Supply
Table_1._Power_Control
VBAT
VCC
+3.3V
VBAT
VCC
VBAT
VCC
+3.3V
CONFIGURATION CONDITION I/O_ACTIVE I/O_INACTIVE RST
VCC Only
(Figure 4)
VCC > VPF ICCA ICCS Inactive (High)
VCC < VPF Active (Low)
VBAT Only
(Figure 5)
EOSC = 0 IBATA IBATT Disabled (Low)
EOSC = 1 IBATDR
Dual Supply
(Figure 6)
VCC > VPF ICCA ICCS Inactive (High)
VCC < VPF VCC > VBAT ICCA VCC > VBAT ICCS Active (Low)
VCC < VBAT IBATA VCC < VBAT IBATT
DS3231M
Maxim Integrated
9
±5ppm, I2C Real-Time Clock
by VCC. If VCC is less than VPF and is less than VBAT, the
device is powered by VBAT (see Table 1).
When VCC < VPF, the RST output is asserted (active
low). When VCC is the presently selected power source,
temperature conversions are executed once per second.
When VBAT is the presently selected power source, tem-
perature conversions are executed once every 10s.
To preserve the battery, the first time VBAT is applied
to the device the oscillator does not start up until VCC
exceeds VPF or until a valid I2C address is written to
the device. Typical oscillator startup time is less than
1s. Approximately 2s 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 tem-
perature and correct the oscillator frequency. On the first
application of VCC power, or (if VBAT powered) when a
valid I2C address is written to the device, the time and
date registers are reset to 01/01/00 01 00:00:00 (DD/MM/
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,
the active battery current IBATA is drawn. When the
serial interface is inactive, the timekeeping current IBATT
(which includes the averaged temperature-conversion
current IBATTC) is used. The 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. The data-retention
current IBATDR is the current drawn by the device when
the oscillator is stopped (EOSC = 1). This mode can be
used to minimize battery requirements for periods 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 device provides for a pushbutton switch to be con-
nected to the RST input/output pin. When the device is
not in a reset cycle, it continuously monitors RST for a
low-going edge. If an edge transition is detected, the
device debounces the switch by pulling RST low. After
the internal timer has expired (PBDB), the device con-
tinues to monitor the RST line. If the line is still low, the
device continuously monitors the line looking for a rising
edge. Upon detecting release, the device forces RST
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 RST
low. When VCC returns to a level above VPF, RST is held
low for approximately 250ms (tREC) to allow the power
supply to stabilize. If the oscillator is not running when
VCC is applied, tREC is bypassed and RST immedi-
ately goes high. Assertion of the RST output, whether by
pushbutton or power-fail detection, does not affect the
device’s internal operation. RST output operation and
pushbutton monitoring are only available if VCC power
is available.
Real-Time Clock (RTC)
With the 1Hz source from the temperature-compensated
oscillator, 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 the
12-hour format with an AM/PM indicator. The clock pro-
vides two programmable time-of-day alarms. INT/SQW
can be enabled to generate either an interrupt due to an
alarm condition or a 1Hz square wave. This selection is
controlled by the INTCN bit in the Control register.
I2C Interface
The I2C interface is accessible whenever either VCC or
VBAT is at a valid level. If a microcontroller connected
to the device resets because of a loss of VCC or other
event, it is possible that the microcontroller and device’s
I2C communications could become unsynchronized,
e.g., the microcontroller resets while reading data from
the device. When the microcontroller resets, the device’s
I2C interface can be placed into a known state by tog-
gling 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.
Address Map
Table 2 shows the address map for the device’s 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 cur-
rent time is transferred to a second set of registers. The
time information is read from these secondary registers,
while the clock can continue to run. This eliminates the
need to reread the registers in case the main registers
update during a read.
DS3231M
10
Maxim Integrated
±5ppm, I2C Real-Time Clock
Clock and Calendar
The time and calendar information is obtained by read-
ing the appropriate register bytes. Table 2 shows 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 the
binary-coded decimal (BCD) format. The device can
be run in either 12-hour or 24-hour mode. Bit 6 of the
Hours register is defined as the 12-hour 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 regis-
ter) is toggled when the Years register overflows from 99
Table_2._Timekeeping_Registers
Note: Unless otherwise specified, the registers’ state is not defined when power is first applied.
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
AM/PM 10
Hours Hour Hours
1–12 +
AM/PM
00–23
20
Hours
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
09h A1M3 12/24
AM/PM 10
Hours Hour Alarm 1 Hours
1–12 +
AM/PM
00–23
20
Hours
0Ah A1M4 DY/DT 10 Date Day Alarm 1 Day 1–7
Date Alarm 1 Date 1–31
0Bh A2M2 10 Minutes Minutes Alarm 2
Minutes 00–59
0Ch A2M3 12/24
AM/PM 10
Hours Hour Alarm 2 Hours
1–12 +
AM/PM
00–23
20
Hours
0Dh A2M4 DY/DT 10 Date Day Alarm 2 Day 1–7
Date Alarm 2 Date 1–31
0Eh EOSC BBSQW CONV NA NA INTCN A2IE A1IE Control —
0Fh OSF 0 0 0 EN32KHZ BSY A2F A1F Status —
10h SIGN DATA DATA DATA DATA DATA DATA DATA Aging Offset 81h–7Fh
11h SIGN DATA DATA DATA DATA DATA DATA DATA Temperature
MSB —
12h DATA DATA 0 0 0 0 0 0 Temperature
LSB —
DS3231M
Maxim Integrated
11
±5ppm, I2C Real-Time Clock
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, secondary buffers
are used to prevent errors when the internal registers
update. When reading the time and date registers, the
secondary buffers are synchronized to the internal reg-
isters on any I2C 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 countdown
chain is reset whenever the seconds register is writ-
ten. Write transfers occur on the acknowledge from the
device. Once the countdown chain is reset, to avoid roll-
over issues the remaining time and date registers must
be written within 1s.
Alarms
The device contains two time-of-day/date alarms. Alarm
1 can be set by writing to registers 07h–0Ah. Alarm
2 can be set by writing to registers 0Bh–0Dh. See
Table 2. The alarms can be programmed (by the alarm
enable and INTCN bits in the Control register) to acti-
vate 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 3 shows the
possible settings. Configurations not listed in the table
result in illogical operation. The DY/DT bits (bit 6 of the
alarm day/date registers) control whether the alarm
value stored in bits 0–5 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 is the result of a match with date of
the month. If DY/DT is written to logic 1, the alarm is the
result of a match with day of the week. When the RTC
register values match alarm register settings, the cor-
responding alarm flag A1F or A2F bit is set to logic 1. If
the corresponding alarm interrupt enable A1IE or A2IE
bit is also set to logic 1, the alarm condition activates
the INT/SQW signal if the INTCN bit is set to logic 1. The
match is tested on the once-per-second update of the
time and date registers.
Table_3._Alarm_Mask_Bits
DY/DT ALARM_1_REGISTER_MASK_BITS_(BIT_7) ALARM_RATE
A1M4 A1M3 A1M2 A1M1
X 1 1 1 1 Alarm once a 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 ALARM_2_REGISTER_MASK_BITS_(BIT_7) ALARM_RATE
A2M4 A2M3 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
DS3231M
12
Maxim Integrated
±5ppm, I2C Real-Time Clock
Control Register (0Eh)
BIT_7 BIT_6 BIT_5 BIT_4 BIT_3 BIT_2 BIT_1 BIT_0
EOSC BBSQW CONV NA NA INTCN A2IE A1IE
0 0 0 1 1 1 0 0
BIT 7
EOSC: Enable oscillator. When set to logic 0, the oscillator is started. When set to logic 1, the oscillator is
stopped when the device switches to VBAT. This bit is clear (logic 0) when power is first applied. When the
device is powered by VCC, the oscillator is always on regardless of the status of the EOSC bit. When the oscil-
lator is disabled, all register data is static.
BIT 6
BBSQW: Battery-backed square-wave enable. When set to logic 1 with INTCN = 0 and VCC < VPF, this bit
enables the 1Hz square wave. When BBSQW is logic 0, INT/SQW goes high impedance when VCC falls below
VPF. This bit is disabled (logic 0) when power is first applied.
BIT 5
CONV: Convert temperature. Setting this bit to 1 forces the temperature sensor to convert the temperature
into digital code and execute the temperature compensate algorithm to update the oscillator’s accuracy. The
device cannot be forced to execute the temperature-compensate algorithm faster than once per second. A
user-initiated temperature conversion does not affect the internal update cycle. The CONV bit remains at a 1
from the time it is written until the temperature conversion is completed, 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. See Figure 7 for
more details.
BITS 4:3 NA: Not applicable. These bits have no affect on the device and can be set to either 0 or 1.
BIT 2
INTCN: Interrupt control. This bit controls the INT/SQW output signal. When the INTCN bit is set to logic 0, a
1Hz square wave is output on INT/SQW. When the INTCN bit is set to logic 1, a match between the timekeep-
ing 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 a logic
1 when power is first applied.
BIT 1
A2IE: Alarm 2 interrupt enable. When set to logic 1, this bit permits the alarm 2 flag (A2F) bit in the status reg-
ister 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
A1IE: Alarm 1 interrupt enable. When set to logic 1, this bit permits the alarm 1 flag (A1F) bit in the status reg-
ister 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 an interrupt signal. The A1IE bit is disabled (logic 0) when power is first applied.
DS3231M
Maxim Integrated
13
±5ppm, I2C Real-Time Clock
Figure 7. CONV Control Bit and BSY Status Bit Operation
VCC POWERED
VBAT POWERED
INTERNAL 1Hz
CLOCK
BSY
CONV
INTERNAL 1Hz
CLOCK
BSY
CONV
THE USER SETS THE CONV BIT
THE USER SETS THE CONV BIT
10 SECONDS
THE DEVICE CLEARS THE CONV BIT
AFTER THE TEMPERATURE CONVERSION
HAS COMPLETED
THE DEVICE CLEARS THE CONV BIT
AFTER THE TEMPERATURE CONVERSION
HAS COMPLETED
BSY IS HIGH DURING
THE TEMPERATURE CONVERSION
DS3231M
14
Maxim Integrated
±5ppm, I2C Real-Time Clock
Status Register (0Fh)
Aging Offset Register (10h)
BIT_7 BIT_6 BIT_5 BIT_4 BIT_3 BIT_2 BIT_1 BIT_0
OSF 0 0 0 EN32KHZ BSY A2F A1F
1 0 0 0 1 X X X
BIT 7
OSF: Oscillator stop flag. A logic 1 in this bit indicates that the oscillator either is stopped or was stopped for
some period and could be used to judge the validity of the timekeeping data. This bit is set to logic 1 any time
that the oscillator stops. This bit remains at logic 1 until written to logic 0. 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 the oscillator.
3) The EOSC bit is turned off in battery-backed mode.
4) External influences on the oscillator (i.e., noise, leakage, etc.).
BITS 6:4 Unused (0). These bits have no meaning and are fixed at 0 when read.
BIT 3
EN32KHZ: Enabled 32.768kHz output. This bit enables and disables the 32KHZ output. When set to a logic 0,
the 32KHZ output is high impedance. On initial power-up, this bit is set to a logic 1 and the 32KHZ output is
enabled and produces a 32.768kHz square wave if the oscillator is enabled.
BIT 2
BSY: Busy. This bit indicates the device is busy executing temperature conversion function. It goes to logic 1
when the conversion signal to the temperature sensor is asserted, and then it is cleared when the device has
completed the temperature conversion. See the Block Diagram for more details.
BIT 1
A2F: Alarm 2 flag. 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, INT/SQW 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
A1F: Alarm 1 flag. A logic 1 in the alarm 1 flag bit indicates that the time matched the alarm 1 registers. If the
A1IE bit is logic 1 and the INTCN bit is set to logic 1, INT/SQW 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 BIT_6 BIT_5 BIT_4 BIT_3 BIT_2 BIT_1 BIT_0
SIGN DATA DATA DATA DATA DATA DATA DATA
0 0 0 0 0 0 0 0
The Aging Offset register takes a user-provided value to add to or subtract from the factory-trimmed value that adjusts the
accuracy of the time base. Use of the Aging Offset register is not needed to achieve the accuracy as defined in the Electrical
Characteristics tables.
The Aging Offset code is encoded in two’s complement, with bit 7 representing the SIGN bit and a valid range of ±127. One
LSB typically represents a 0.12ppm change in frequency. The change in ppm per LSB is the same over the operating tempera-
ture range. Positive offsets slow the time base and negative offsets quicken the time base.
DS3231M
Maxim Integrated
15
±5ppm, I2C Real-Time Clock
I2C Serial Port Operation
I2C Slave Address
The device’s slave address byte is D0h. The first byte
sent to the device includes the device identifier, device
address, and the R/W bit (Figure 8). The device address
sent by the I2C master must match the address assigned
to the device.
I2C Definitions
The following terminology is commonly used to describe
I2C data transfers.
Master_Device: The master device controls the slave
devices on the bus. The master device generates
SCL clock pulses and START and STOP conditions.
Slave_Devices: Slave devices send and receive data
at the master’s request.
Bus_ Idle_ or_ Not_ Busy: Time between STOP and
START conditions when both SDA and SCL are
inactive and in their logic-high states. When the bus
is idle, it often initiates a low-power mode for slave
devices.
START_Condition: A START condition is generated
by the master to initiate a new data transfer with a
slave. Transitioning SDA from high to low while SCL
remains high generates a START condition. See
Figure 1 for applicable timing.
STOP_ Condition: A STOP condition is generated
by the master to end a data transfer with a slave.
Transitioning SDA from low to high while SCL remains
high generates a STOP condition. See Figure 1 for
applicable timing.
Repeated_ START_ Condition: The master can use
a repeated START condition at the end of one data
transfer to indicate that it immediately initiates a new
data transfer following the current one. Repeated
STARTs are commonly used during read operations
to identify a specific memory address to begin a data
transfer. A repeated START condition is issued iden-
tically to a normal START condition. See Figure 1 for
applicable timing.
Temperature Registers (11h-12h)
Figure 8. I2C Slave Address Byte
1 1 10 R/W000
MSB LSB
READ/
WRITE BIT
DEVICE
IDENTIFIER
Temperature_Register_(Upper_Byte_=_11h)
BIT_7 BIT_6 BIT_5 BIT_4 BIT_3 BIT_2 BIT_1 BIT_0
SIGN DATA DATA DATA DATA DATA DATA DATA
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
DATA DATA 0 0 0 0 0 0
0 0 0 0 0 0 0 0
Temperature is represented as a 10-bit code with a resolution of 0.25°C and is accessible at location 11h and 12h. The tem-
perature 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 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 upon initial applica-
tion of VCC or I2C access on VBAT and once every second afterwards with VCC power or once every 10s with VBAT power. The
Temperature registers are also updated after each user-initiated conversion and are read only.
DS3231M
16
Maxim Integrated
±5ppm, I2C Real-Time Clock
Bit_ Write: Transitions of SDA must occur during
the low state of SCL. The data on SDA must remain
valid and unchanged during the entire high pulse of
SCL plus the setup and hold time requirements (see
Figure 1). Data is shifted into the device during the
rising edge of the SCL.
Bit_Read: At the end of a write operation, the master
must release the SDA bus line for the proper amount
of setup time (see Figure 1) before the next rising
edge of SCL during a bit read. The device shifts out
each bit of data on SDA at the falling edge of the
previous SCL pulse and the data bit is valid at the
rising edge of the current SCL pulse. Remember that
the master generates all SCL clock pulses including
when it is reading bits from the slave.
Acknowledge_ (ACK_ and_ NACK): An acknowledge
(ACK) or not acknowledge (NACK) is always the
ninth bit transmitted during a byte transfer. The
device receiving data (the master during a read or
the slave during a write operation) performs an ACK
by transmitting a 0 during the ninth bit. A device per-
forms a NACK by transmitting a 1 during the ninth bit.
Timing for the ACK and NACK is identical to all other
bit writes. An ACK is the acknowledgment that the
device is properly receiving data. A NACK is used to
terminate a read sequence or as an indication that the
device is not receiving data.
Byte_Write: A byte write consists of 8 bits of informa-
tion transferred from the master to the slave (most
significant bit first) plus a 1-bit acknowledgment from
the slave to the master. The 8 bits transmitted by the
master are done according to the bit write definition
and the acknowledgment is read using the bit read
definition.
Byte_Read: A byte read is an 8-bit information transfer
from the slave to the master plus a 1-bit ACK or NACK
from the master to the slave. The 8 bits of information
that are transferred (most significant bit first) from the
slave to the master are read by the master using the
bit read definition, and the master transmits an ACK
using the bit write definition to receive additional data
bytes. The master must NACK the last byte read to
terminate communication so the slave returns control
of SDA to the master.
Slave_ Address_ Byte: Each slave on the I2C bus
responds to a slave address byte sent immediately
following a START condition. The slave address byte
contains the slave address in the most significant 7
bits and the R/W bit in the least significant bit. The
device’s slave address is D0h and cannot be modi-
fied by the user. When the R/W bit is 0 (such as in
D0h), the master is indicating it writes data to the
slave. If R/W = 1 (D1h in this case), the master is
indicating it wants to read from the slave. If an incor-
rect slave address is written, the device assumes the
master is communicating with another I2C device
and ignore the communication until the next START
condition is sent.
Memory_Address: During an I2C write operation, the
master must transmit a memory address to identify
the memory location where the slave is to store the
data. The memory address is always the second byte
transmitted during a write operation following the
slave address byte.
I2C Communication
See Figure 9 for an I2C communication example.
Writing_a_Single_Byte_to_a_Slave: The master must
generate a START condition, write the slave address
byte (R/W = 0), write the memory address, write
the byte of data, and generate a STOP condition.
Remember the master must read the slave’s acknowl-
edgment during all byte write operations.
Writing_Multiple_Bytes_to_a_Slave: To write multiple
bytes to a slave, the master generates a START con-
dition, writes the slave address byte (R/W = 0), writes
the starting memory address, writes multiple data
bytes, and generates a STOP condition.
Reading_a_Single_Byte_from_a_Slave: Unlike the write
operation that uses the specified memory address
byte to define where the data is to be written, the read
operation occurs at the present value of the memory
address counter. To read a single byte from the slave,
the master generates a START condition, writes the
slave address byte with R/W = 1, reads the data byte
with a NACK to indicate the end of the transfer, and
generates a STOP condition. However, since requir-
ing the master to keep track of the memory address
counter is impractical, use the method for manipulat-
ing the address counter for reads.
Manipulating_ the_ Address_ Counter_ for_ Reads: A
dummy write cycle can be used to force the address
counter to a particular value. To do this the mas-
ter generates a START condition, writes the slave
address byte (R/W = 0), writes the memory address
where it desires to read, generates a repeated START
condition, writes the slave address byte (R/W = 1),
DS3231M
Maxim Integrated
17
±5ppm, I2C Real-Time Clock
reads data with ACK or NACK as applicable, and
generates a STOP condition. See Figure 6 for a read
example using the repeated START condition to
specify the starting memory location.
Reading_ Multiple_ Bytes_ from_ a_ Slave: The read
operation can be used to read multiple bytes with a
single transfer. When reading bytes from the slave,
the master simply ACKs the data byte if it desires to
read another byte before terminating the transaction.
After the master reads the last byte it must NACK to
indicate the end of the transfer and then it generates
a STOP condition.
Applications Information
Power-Supply Decoupling
To achieve the best results when using the DS3231M,
decouple the VCC and/or VBAT power supplies with
0.1FF and/or 1.0FF capacitors. Use a high-quality,
ceramic, surface-mount capacitor if possible. Surface-
mount components minimize lead inductance, which
improves performance, and ceramic capacitors tend to
have adequate high-frequency response for decoupling
applications.
If communications during battery operation are not
required, the VBAT decoupling capacitor can be omitted.
Using Open-Drain Outputs
The 32KHZ and INT/SQW outputs are open drain and
therefore require external pullup resistors to realize logic-
high output levels. Pullup resistor values between 1kI
and 10MI are typical.
The RST output is also open drain, but is provided with
an internal 50kI pullup resistor (RPU) to VCC. External
pullup resistors should not be added.
SDA and SCL Pullup Resistors
SDA is an open-drain output and requires an external
pullup resistor to realize a logic-high level.
Because the device does not use clock cycle stretching,
a master using either an open-drain output with a pullup
resistor or CMOS output driver (push-pull) could be used
for SCL.
Battery Charge Protection
The device contains Maxim’s redundant battery-charge
protection circuit to prevent any charging of the external
battery.
Figure 9. I2C Transactions
SLAVE
ADDRESS
START
START
1 1 0 1 0 0 0 SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
R/W
MSB LSB MSB LSB MSB LSB
b7 b6 b5 b4 b3 b2 b1 b0
READ/
WRITE
REGISTER ADDRESS
b7 b6 b5 b4 b3 b2 b1 b0
DATA
STOP
SINGLE BYTE WRITE
-WRITE CONTROL REGISTER
TO 44h
MULTIBYTE WRITE
-WRITE DATE REGISTER
TO "02" AND MONTH
REGISTER TO "11"
SINGLE BYTE READ
-READ CONTROL REGISTER
MULTIBYTE READ
-READ ALARM 2 HOURS
AND DATE VALUES
START REPEATED
START
D1h
MASTER
NACK STOP11010000 00001110
0Eh
11010001
1 1 0 1 0 0 0 0 0 0 0 0 1 1 1 0
D0h 0Eh
STOP
VALUE
START 1 1 0 1 0 0 0 0 0 0 0 0 0 1 0 0
D0h 04h
DATA
MASTER
NACK STOPVALUE
DATA
02h
44h
EXAMPLE I2C TRANSACTIONS
TYPICAL I2C WRITE TRANSACTION
01000100
00000010
D0h
A)
C)
B)
D)
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
REPEATED
START
D1h
MASTER
ACK
11010001 VALUE
DATA
SLAVE
ACK
SLAVE
ACK
SLAVE
ACK
START 1 1 0 1 0 0 0 0 0 0 0 0 1 1 0 0
D0h 0Ch
SLAVE
ACK
SLAVE
ACK
STOP
11h
00010001 SLAVE
ACK
DS3231M
18
Maxim Integrated
±5ppm, I2C Real-Time Clock
Package Information
For the latest package outline information and land patterns (footprints), 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 OUTLINE_NO. LAND_PATTERN_NO.
16 SO W16MK+1 21-0042 90-0107
8 SO S8MK+1 21-0041 90-0096
DS3231M
Maxim Integrated
19
±5ppm, I2C Real-Time Clock
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 6/10 Initial release —
1 5/11
Updated the Features section; moved the temperature accuracy limit from ±3°C (max)
to ±3°C (typ) in the DC Electrical Characteristics—General table; added the Power-
Supply Current vs. SCL Frequency graph to the Typical Operating Characteristics
section; changed the initial date information to international format in the Power-Supply
Configuration section
1, 3, 6, 10
2 10/11
Removed future status from the 8-pin SO package in the Ordering Information table;
updated the Typical Operating Circuit; added Note 7 to the CBIN parameter in the AC
Electrical Characteristics—I2C Interface table; clarified the 10h register range in Table
2 and the Aging Offset Register (10h) section; corrected the package codes for both
SO variants in the Package Information table
1, 4, 11, 15,
19
3 12/11
Added the automotive qualified 8-pin SO package to the Ordering Information table;
changed the lead temperature from +260°C to +300°C in the Absolute Maximum
Ratings section
1, 2
DS3231M