DS3234S#-DS3234SN#-DS3234SN#T&R Fast Delivery |IC PHOENIX CO.,LIMITED

DS3234SN#T&R ,Extremely Accurate SPI Bus RTC with Integrated Crystal and SRAMElectrical Characteristics (continued)(V = 2.0V to 5.5V, V = active supply (see Table 1), T = -40°C ..
DS32506 ,6-/8-/12-Port DS3/E3/STS-1 LIUFEATURES......12 5.8 SPI SERIAL MICROPROCESSOR INTERFACE
DS32506N ,6-/8-/12-Port DS3/E3/STS-1 LIUFEATURES ..11 5.2 RECEIVER.......11 5.3 TRANSMITTER .11 5.4 JITTER ATTENUATOR11 5.5 BIT ERROR-RATE ..
DS32506N+ ,6-/8-/12-Port DS3/E3/STS-1 LIUFUNCTIONAL DESCRIPTION 24 8.1 LIU MODE ......24 8.2 TRANSMITTER .24 8.2.1 Transmit Clock ...... 24 ..
DS32506N+ ,6-/8-/12-Port DS3/E3/STS-1 LIUFUNCTIONAL DESCRIPTION 24 8.1 LIU MODE ......24 8.2 TRANSMITTER .24 8.2.1 Transmit Clock ...... 24 ..
DS32506NA2 ,6-/8-/12-Port DS3/E3/STS-1 LIUapplications. Each LIU port in Standards-Compliant Transmit Waveshaping these devices has independ ..
EA29 ,COMPACT AND LIGHTWEIGHTDATA SHEETMINIATURE SIGNAL RELAYEA2 SERIESCOMPACT AND LIGHTWEIGHTDESCRIPTIONThe EA2 series has red ..
EA2-9 ,COMPACT AND LIGHTWEIGHTDATA SHEETMINIATURE SIGNAL RELAYEA2 SERIESCOMPACT AND LIGHTWEIGHTDESCRIPTIONThe EA2 series has red ..
EA2-9NJ ,COMPACT AND LIGHTWEIGHTFEATURESª Low power consumptionª Compact and light weightª 2 form c contact arrangementª Low magnet ..
EA2-9NU ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
EB2-12 ,COMPACT AND LIGHT WEIGHT SURFACE MOUNTING TYPEFEATURESª Compact and lightweight : 7.5 mm · 14.3 mm · 9.3 mm, 1.5 gª 2 form c contact arrangementª ..
EB2-12NU ,COMPACT AND LIGHT WEIGHT SURFACE MOUNTING TYPEAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..

DS3234S#-DS3234SN#-DS3234SN#T&R
Extremely Accurate SPI Bus RTC with Integrated Crystal and SRAM
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
General Description
The DS3234 is a low-cost, extremely accurate SPI bus
real-time clock (RTC) with an integrated temperature-com-
pensated crystal oscillator (TCXO) and crystal. The
DS3234 incorporates a precision, temperature-compen-
sated voltage reference and comparator circuit to monitor
VCC. When VCCdrops below the power-fail voltage (VPF),
the device asserts the RSToutput and also disables read
and write access to the part when VCCdrops below both
VPFand VBAT. The RSTpin is monitored as a pushbutton
input for generating a µP reset. The device switches to the
backup supply input and maintains accurate timekeeping
when main power to the device is interrupted. The integra-
tion of the crystal resonator enhances the long-term accu-
racy of the device as well as reduces the piece-part count
in a manufacturing line. The DS3234 is available in com-
mercial and industrial temperature ranges, and is offered
in an industry-standard 300-mil, 20-pin SO package.
The DS3234 also integrates 256 bytes of battery-backed
SRAM. In the event of main power loss, the contents of
the memory are maintained by the power source con-
nected to the VBATpin. The RTC maintains seconds,
minutes, hours, day, date, month, and year information.
The date at the end of the month is automatically adjust-
ed for months with fewer than 31 days, including correc-
tions for leap year. The clock operates in either the
24-hour or 12-hour format with AM/PM indicator. Two
programmable time-of-day alarms and a programmable
square-wave output are provided. Address and data
are transferred serially by an SPI bidirectional bus.
Applications
ServersUtility Power Meters
TelematicsGPS
Benefits and FeaturesHighly Accurate RTC with Integrated Crystal and
SRAM Completely Manages All Timekeeping
Functions Accuracy ±2ppm from 0°C to +40°CAccuracy ±3.5ppm from -40°C to +85°CReal-Time Clock Counts Seconds, Minutes, Hours,
Day, Date, Month, and Year, with Leap Year
Compensation Valid Up to 2099Digital Temp Sensor Output: ±3°C AccuracyRegister for Aging TrimRSTInput/OutputTwo Time-of-Day AlarmsProgrammable Square-Wave OutputSimple Serial Interface Connects to Most
Microcontrollers4MHz SPI Bus Supports Modes 1 and 3Battery-Backup Input for Continuous TimekeepingLow Power Operation Extends Battery Backup Run
TimeOperating Temperature Ranges: Commercial: 0°C to
+70°C, Industrial: -40°C to +85°C300-Mil, 20-Pin SO PackageUnderwriters Laboratories®(UL) Recognized
Ordering Information
PART TEMP RANGE PIN-
PACKAGE
TOP
MARK
DS3234S# 0°C to +70°C 20 SO DS3234S
DS3234SN# -40°C to +85°C 20 SO DS3234SN
DS3234
INT/SQW
32kHz
VBAT
PUSH-
BUTTON
RESET
SCLK
RST
N.C.
N.C.
N.C.
VCCVPU
VCC
GND
VCC
SCLK
DINMOSI
DOUTMISO
RST
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
Typical Operating Circuit
#Denotes an RoHS-compliant device that may include lead(Pb)
that is exempt under the RoHS requirements. Lead finish is
JESD97 Category e3, and is compatible with both lead-based
and lead-free soldering processes. A "#" anywhere on the top
mark denotes an RoHS-compliant device.
Underwriters Laboratories Inc. is a registered certification mark
of Underwriters Laboratories Inc.
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Absolute Maximum Ratings
Recommended Operating Conditions
(TA= -40°C to +85°C, unless otherwise noted.) (Notes 2, 3)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage Range on Any Pin Relative to Ground......-0.3V to +6.0V
Junction-to-Ambient Thermal Resistance (θJA) (Note 1)...55°C/W
Junction-to-Case Thermal Resistance (θJC) (Note 1)........24°C/W
Operating Temperature Range
(noncondensing).............................................-40°C to +85°C
Junction Temperature......................................................+125°C
Storage Temperature Range...............................-40°C to +85°C
Lead Temperature (soldering, 10s).................................+260°C
Soldering Temperature (reflow, 2 times max)....................+260°C
(See the Handling, PC Board Layout, and Assemblysection.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
VCC 2.0 3.3 5.5 Supply Voltage VBAT 2.0 3.0 3.8 V
Logic 1 Input CS, SCLK, DIN VIH0.7 x
VCC
VCC +
0.3 V
2.0V VCC 3.63V -0.3 +0.2 x
VCCLogic 0 Input CS, SCLK, DIN,
RSTVIL
3.63V < VCC 5.5V -0.3 +0.7
Electrical Characteristics
(VCC= 2.0V to 5.5V, VCC= active supply (see Table 1), TA= -40°C to +85°C, unless otherwise noted.) (Typical values are at VCC=
3.3V, VBAT= 3.0V, and TA= +25°C, unless otherwise noted. TCXO operation guaranteed from 2.3V to 5.5V on VCCand 2.3V to 3.8V on
VBAT.) (Notes 2, 3)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
VCC = 3.63V400Active Supply CurrentICCASCLK = 4MHz, BSY = 0
(Notes 4, 5)VCC = 5.5V700µA
VCC = 3.63V120
Standby Supply CurrentICCS
CS = VIH, 32kHz output off,
SQW output off
(Note 5)VCC = 5.5V160
VCC = 3.63V500Temperature Conversion CurrentICCSCONVSPI bus inactive, 32kHz
output off, SQW output offVCC = 5.5V600µA
Power-Fail VoltageVPF2.452.5752.70V
VBAT Leakage CurrentIBATLKG25100nA
(VCC = 2.0V to 5.5V, TA = -40°C to +85°C, unless otherwise noted.) (Notes 2 and 3)
Logic 1 Output, 32kHz
IOH = -500µA
IOH = -250µA
IOH = -125µA
VOH
VCC > 3.63V,
3.63V > VCC > 2.7V,
2.7V > (VCC or VBAT) > 2.0V
(BB32kHz = 1)
0.85 x VCCV
Note 1:Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Electrical Characteristics (continued)
(VCC= 2.0V to 5.5V, VCC= active supply (see Table 1), TA= -40°C to +85°C, unless otherwise noted.) (Typical values are at VCC=
3.3V, VBAT= 3.0V, and TA= +25°C, unless otherwise noted. TCXO operation guaranteed from 2.3V to 5.5V on VCCand 2.3V to 3.8V on
VBAT.) (Notes 2, 3)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSLogic 0 Output, 32kHz VOL IOL = 1mA 0.4 VLogic 1 Output, DOUT VOH IOH = -1.0mA 0.85 x VCC VLogic 0 Output, DOUT, INT/SQW VOL IOL = 3mA 0.4 VLogic 0 Output, RST VOL IOL = 1.0mA 0.4 VOutput Leakage Current 32kHz,
INT/SQW, DOUT ILO Output high impedance -1 0 +1µAInput Leakage DIN, CS, SCLK ILI -1 +1µARST Pin I/O Leakage IOL RST high impedance (Note 6) -200 +10 µATCXO (VCC = 2.3V to 5.5V, VBAT = 2.3V to 3.8V, TA = -40°C to +85°C, unless otherwise noted.) (Notes 2 and 3)Output Frequency fOUT VCC = 3.3V or VBAT = 3.3V 32.768 kHz0°C to +40°C -2 +2 Frequency Stability vs.
Temperature Δf/fOUT VCC = 3.3V or
VBAT = 3.3V -40°C to 0°C and
+40°C to +85°C -3.5 +3.5 ppmFrequency Stability vs. Voltage Δf/V 1 ppm/V-40°C 0.7 +25°C 0.1 +70°C 0.4 Trim Register Frequency
Sensitivity per LSB Δf/LSB Specified at:+85°C 0.8 ppm
Temperature AccuracyTemp-3+3°C
First year±1.0Crystal AgingΔf/fOUTAfter reflow,
not production tested0–10 years±5.0ppm
Electrical Characteristics
(VCC= 0V, VBAT= 2.0V to 3.8V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
VBAT = 3.4V1.52.3Timekeeping Battery Current
(Note 5)IBATTEOSC = 0, BBSQW = 0,
CRATE1 = CRATE0 = 0VBAT = 3.8V1.52.5µA
Temperature Conversion CurrentIBATTCEOSC = 0, BBSQW = 0400µA
Data-Retention CurrentIBATTDREOSC = 1100nA
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Electrical Characteristics
(VCC= 2.0V to 5.5V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
2.7V ≤ VCC ≤ 5.5V4SCLK Clock FrequencyfSCL2.0V ≤ VCC < 2.7V2MHz
Data to SCLK SetuptDC30ns
SCLK to Data HoldtCDH30ns
SCLK to CS SetuptCCS30ns
2.7V ≤ VCC ≤ 5.5V80SCLK to Data Valid (Note 7)tCDD2.0V ≤ VCC < 2.7V160ns
2.7V ≤ VCC ≤ 5.5V110SCLK Low TimetCL2.0V ≤ VCC < 2.7V220ns
2.7V ≤ VCC ≤ 5.5V110SCLK High TimetCH2.0V ≤ VCC < 2.7V220ns
SCLK Rise and FalltR, tF200ns
CS to SCLK SetuptCC400ns
2.7V ≤ VCC ≤ 5.5V100SCLK to CS HoldtCCH2.0V ≤ VCC < 2.7V200ns
CS Inactive TimetCWH400ns
CS to Output High ImpedancetCDZ(Note 8)40ns
Pushbutton DebouncePBDB250ms
Reset Active TimetRST250ms
Oscillator Stop Flag (OSF) DelaytOSF(Note 9)100ms
Temperature Conversion TimetCONV125200ms
Power-Switch Characteristics
5(TA= -40°C to +85°C)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
VCC Fall Time; VPF(MAX) to
VPF(MIN)tVCCF300µs
VCC Rise Time; VPF(MIN) to
VPF(MAX)tVCCR0µs
Recovery at Power-UptREC(Note 10)125300ms
Capacitance
(TA= +25°C)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Capacitance on All Input PinsCIN(Note 11)10pF
Capacitance on All Output PinsCIOOutputs high impedance (Note 11)10pF
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Pushbutton Reset Timing
tRSTPBDB
RST
Power-Switch Timing
VCC
VPF(MAX)
RSTPF(MIN)
tVCCFtVCCR
tREC
VPFVPF
Note 2:Limits at -40°C are guaranteed by design and not production tested.
Note 3:All voltages are referenced to ground.
Note 4:Measured at VIH= 0.8 x VCCor VIL= 0.2 x VCC, 10ns rise/fall time, DOUT = no load.
Note 5:Current is the averaged input current, which includes the temperature conversion current. CRATE1 = CRATE0 = 0.
Note 6:The RSTpin has an internal 50kΩ(nominal) pullup resistor to VCC.
Note 7:Measured at VOH= 0.8 x VCCor VOL= 0.2 x VCC. Measured from the 50% point of SCLK to the VOHminimum of DOUT.
Note 8:With 50pF load.
Note 9:The parameter tOSFis the period of time the oscillator must be stopped for the OSF flag to be set over the voltage range of
0V ≤VCC≤VCC(MAX) and 2.3V ≤VBAT≤VBAT(MAX).
Note 10:This delay only applies if the oscillator is enabled and running. If the EOSCbit is 1, tRECis bypassed and RSTimmediately
goes high.
Note 11:Guaranteed by design and not production tested.
WARNING: Negative undershoots below -0.3V while the part is in battery-backed mode may
cause loss of data.
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Timing Diagram—SPI Read Transfer
HIGH IMPEDANCE
SCLK
DIN
W/R
tDC
tCLtCH
tCDD
tCDZ
tCDH
tCC
tCCStFA0
WRITE ADDRESS BYTE
NOTE: SCLK CAN BE EITHER POLARITY, SHOWN FOR CPOL = 1.
READ DATA BYTE
DOUT
Timing Diagram—SPI Write Transfer
SCLK
DIN
W/R
tDC
tCDHtCLtCH
tCCH
tCWHtRtCCA0
WRITE ADDRESS BYTEWRITE DATA BYTED0
DOUTHIGH IMPEDANCE
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
DS3234 toc01
VCC (V)
SUPPLY CURRENT (
RST ACTIVEINPUTS = GND
BATTERY CURRENT
vs. SUPPLY VOLTAGE
DS3234 toc02
SUPPLY VOLTAGE (VBAT)
SUPPLY CURRENT (nA)
VCC = 0V
BB32kHz = 0
BBSQW = 1
BBSQW = 0
BATTERY CURRENT
vs. TEMPERATURE
DS3234 toc03
TEMPERATURE (°C)
SUPPLY CURRENT (nA)6040-20020
VBAT = 3.4V
VBAT = 3.0V
VCC = 0V
BB32kHz = 0
BBSQW = 0
FREQUENCY DEVIATION
vs. TEMPERATURE vs. AGING VALUE
DS3234 toc04
TEMPERATURE (°C)
FREQUENCY DEVIATION (ppm)6040-20020
AGING = -128
AGING = -33
AGING = 127
AGING = 0
AGING = 32
ICCA vs. DOUT LOAD
DS3234 toc05
CAPACITANCE (pF)
SUPPLY CURRENT (302010
SCLK = 4MHz
DELTA TIME AND FREQUENCY
vs. TEMPERATURE
TEMPERATURE (°C)
DELTA FREQUENCY (ppm)
DELTA TIME (MIN/YEAR)705060-10010203040-30-20
DS3234 toc06
CRYSTAL
+20ppm
CRYSTAL
-20ppm
TYPICAL CRYSTAL,
UNCOMPENSATED
DS3234
ACCURACY
BAND
Typical Operating Characteristics
(VCC= +3.3V, TA = +25°C, unless otherwise noted.)
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Pin Description
PINNAMEFUNCTIONCSActive-Low Chip Select Input. Used to select or deselect the device.
2, 7–14N.C.No Connection. Not connected internally. Must be connected to ground.32kHz32kHz Push-Pull Output. If disabled with either EN32kHz = 0 or BB32kHz = 0, the state of the 32kHz pin will be
low.
4VCCDC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1µF to 1.0µF capacitor.INT/SQW
Active-Low Interrupt or Square-Wave Output. This open-drain pin requires an external pullup resistor. 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 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 driven high impedance. 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. On first power-up, or if the crystal
oscillator is disabled, tRST is bypassed and RST immediately goes high.GNDGroundVBAT
Backup Power-Supply Input. If VBAT is not used, connect to ground. Diodes placed in series between the VBAT
pin and the battery can cause improper operation. UL recognized to ensure against reverse charging when
used with a lithium battery. Go to www.maximintegrated.com/qa/info/ul.DINSPI Data Input. Used to shift address and data into the device.
18, 20SCLK
SPI Clock Input. Used to control timing of data into and out of the device. Either clock polarity can be used. The
clock polarity is determined by the device based on the state of SCLK when CS goes low. Pins 18 and 20 are
electrically connected together internally.DOUTSPI Data Output. Data is output on this pin when the device is in read mode; CMOS push-pull driver.
TOP VIEW
SCLK
DOUT
SCLK
DINVCC
32kHz
N.C.
VBAT
GND
N.C.
N.C.N.C.
N.C.
RST
INT/SQW
N.C.
N.C.N.C.
N.C.
DS3234
Pin Configuration
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
Block Diagram
CLOCK AND CALENDAR
REGISTERS
SRAM
USER BUFFER
(7 BYTES)
SPI INTERFACE AND
ADDRESS REGISTER
DECODE
POWER CONTROL
VCC
VBAT
GND
SCLK
SCLK
DIN
DOUT
TEMPERATURE
SENSOR
CONTROL LOGIC/
DIVIDER
CONTROL AND STATUS
REGISTERS
OSCILLATOR AND
CAPACITOR ARRAY
DS3234
RST
VCC
INT/SQW
SQUARE-WAVE BUFFER;
INT/SQW CONTROL
VOLTAGE REFERENCE;
DEBOUNCE CIRCUIT;
PUSHBUTTON RESET
32kHz
Detailed Description
The DS3234 is a TCXO and RTC with integrated crystal
and 256 bytes of SRAM. An integrated sensor periodi-
cally samples the temperature and adjusts the oscilla-
tor load to compensate for crystal drift caused by
temperature variations. The DS3234 provides user-
selectable sample rates. This allows the user to select
a temperature sensor sample rate that allows for vari-
ous temperature rates of change, while minimizing cur-
rent consumption by temperature sensor sampling. The
user should select a sample rate based upon the
expected temperature rate of change, with faster sam-
ple rates for applications where the ambient tempera-
ture changes significantly over a short time. The TCXO
provides a stable and accurate reference clock, and
maintains the RTC to within ±2 minutes per year accu-
racy from -40°C to +85°C. The TCXO frequency output
is available at the 32kHz pin. The RTC is a low-power
clock/calendar with two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW provides either an interrupt signal due to
alarm conditions or a square-wave output. The
clock/calendar provides seconds, minutes, hours, day,
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
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 for-
mat with AM/PM indicator. Access to the internal regis-
ters is possible through an SPI bus interface.
A temperature-compensated voltage reference and
comparator circuit monitors the level of VCCto detect
power failures and to automatically switch to the backup
supply when necessary. When operating from the back-
up supply, access is inhibited to minimize supply cur-
rent. Oscillator, time and date, and TCXO operations can
continue while the backup supply powers the device.
The RSTpin 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
DS3234. The eight blocks can be grouped into four
functional groups: TCXO, power control, pushbutton
function, and RTC. Their operations are described sep-
arately in the following sections.
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 the 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. The tempera-
ture is read on initial application of VCCand once every
64 seconds (default, see the description for CRATE1
and CRATE0 in the Control/Status Registersection)
afterwards.
Power Control
The power control function is provided by a tempera-
ture-compensated voltage reference and a comparator
circuit that monitors the VCClevel. The device is fully
accessible and data can be written and read when VCC
is greater than VPF. However, when VCCfalls below
both VPFand VBAT, the internal clock registers are
blocked from any access. If VPFis less than VBAT, the
device power is switched from VCCto VBATwhen VCC
drops below VPF. If VPFis greater than VBAT, the
device power is switched from VCCto VBATwhen VCC
drops below VBAT. After VCCreturns above both VPF
and VBAT, read and write access is allowed after RST
goes high (Table 1).
To preserve the battery, the first time VBATis applied to
the device, the oscillator does not start up until VCC
crosses VPF. After the first time VCCis ramped up, the
oscillator starts up and the VBATsource powers the
oscillator during power-down and keeps the oscillator
running. When the DS3234 switches to VBAT, the oscil-
lator may be disabled by setting the EOSCbit.
VBATOperation
There are several modes of operation that affect the
amount of VBATcurrent that is drawn. When the part is
powered by VBAT, timekeeping current (IBATT), which
includes the averaged temperature conversion current,
IBATTC, is drawn (refer to Application Note 3644: Power
Considerations for Accurate Real-Time Clocksfor
details). Temperature conversion current, IBATTC, is
specified since the system must be able to support the
periodic higher current pulse and still maintain a valid
voltage level. Data retention current, IBATTDR, is the
current drawn by the part when the oscillator is
stopped (EOSC= 1). This mode can be used to mini-
mize battery requirements for times when maintaining
time and date information is not necessary, e.g., while
the end system is waiting to be shipped to a customer.
Pushbutton Reset Function
The DS3234 provides for a pushbutton switch to be
connected to the RSToutput pin. When the DS3234 is
not in a reset cycle, it continuously monitors the RST
signal for a low going edge. If an edge transition is
detected, the DS3234 debounces the switch by pulling
the RSTlow. After the internal timer has expired
(PBDB), the DS3234 continues to monitor the RSTline.
If the line is still low, the DS3234 continuously monitors
the line looking for a rising edge. Upon detecting
release, the DS3234 forces the RSTpin low and holds it
low for tRST.
The same pin, RST, is used to indicate a power-fail
condition. When VCCis lower than VPF, an internal
power-fail signal is generated, which forces the RSTpin
low. When VCCreturns to a level above VPF, the RST
pin is held low for tRECto allow the power supply to sta-
bilize. If the EOSCbit is set to logic 1 (to disable the
oscillator in battery-backup mode), tRECis bypassed
and RSTimmediately goes high.
SUPPLY CONDITIONREAD/WRITE
ACCESS
ACTIVE
SUPPLYRST
VCC < VPF, VCC < VBATNoVBATActive
VCC < VPF, VCC > VBATYesVCCActive
VCC > VPF, VCC < VBATYesVCCInactive
VCC > VPF, VCC > VBATYesVCCInactive
Table 1. Power Control
DS3234Extremely Accurate SPI Bus RTC
with Integrated Crystal and SRAM
When RSTis active due to a power-fail condition (see
Table 1), SPI operations are inhibited while the TCXO
and RTC continue to operate. When RSTis active due
to a pushbutton event, it does not affect the operation
of the TCXO, SPI interface, or RTC functions.
Real-Time Clock
With the clock source from the TCXO, the RTC provides
seconds, minutes, hours, day, date, month, and year
information. The date at the end of the month is auto-
matically adjusted for months with fewer than 31 days,
including corrections for leap year. The clock operates
in either the 24-hour or 12-hour format with an AM/PM
indicator.
The clock provides two programmable time-of-day
alarms and a programmable square-wave output. The
INT/SQW pin either generates an interrupt due to alarm
condition or outputs a square-wave signal and the
selection is controlled by the bit INTCN.
SRAM
The DS3234 provides 256 bytes of general-purpose
battery-backed read/write memory. The SRAM can be
written or read whenever VCCis above either VPFor
VBAT.
Address Map
Figure 1 shows the address map for the DS3234 time-
keeping registers. During a multibyte access, when the
address pointer reaches the end of the register space
(13h read, 93h write), it wraps around to the beginning
(00h read, 80h write). The DS3234 does not respond to
a read or write to any reserved address, and the inter-
nal address pointer does not increment. Address point-
er operation when accessing the 256-byte SRAM data
is covered in the description of the SRAM address and
data registers. On the falling edge of CS, or during a
multibyte access when the address pointer increments
to location 00h, the current time is transferred to a sec-
ond set of registers. The time information is read from
these secondary registers, while the internal clock reg-
isters continue to increment normally. If the time and
date registers are read using a multibyte read, this
eliminates the need to reread the registers in case the
main registers update during a read.
SPI Interface
The DS3234 operates as a slave device on the SPI seri-
al bus. Access is obtained by selecting the part by thepin and clocking data into/out of the part using the
SCLK and DIN/DOUT pins. Multiple byte transfers are
supported within one CSlow period. The SPI on the
DS3234 interface is accessible whenever VCCis above
either VBATor VPF.
Clock and Calendar
The time and calendar information is obtained by read-
ing the appropriate register bytes. Figure 1 illustrates
the RTC registers. The time and calendar data are set
or initialized by writing the appropriate register bytes.
The contents of the time and calendar registers are in
binary-coded decimal (BCD) format. The DS3234 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, 12-hour mode is selected. In 12-
hour mode, bit 5 is the AM/PM bit with logic-high being
PM. In 24-hour mode, bit 5 is the 20-hour bit (20–23
hours). The century bit (bit 7 of the month register) is
toggled when the years register overflows from 99 to
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 (user) buffers are used to prevent errors
when the internal registers update. When reading the
time and date registers, the user buffers are synchro-
nized to the internal registers on the falling edge of CS
or 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 written. Write transfers occur when the last
bit of a byte is clocked in. 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.

Partno	Mfg	Dc	Qty	Available	Descript
DS3234S#	MAXIM	N/a	1500	avai	Extremely Accurate SPI Bus RTC with Integrated Crystal and SRAM
DS3234SN#	MAXIM	N/a	1500	avai	Extremely Accurate SPI Bus RTC with Integrated Crystal and SRAM
DS3234SN#T&R \|DS3234SNT&R	MAXIM	N/a	3000	avai	Extremely Accurate SPI Bus RTC with Integrated Crystal and SRAM