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DS1672-33+-DS1672S-33+-DS1672S-33+T&R
I²C 32-Bit Binary Counter RTC
GENERAL DESCRIPTION The DS1672 incorporates a 32-bit counter and
power-monitoring functions. The 32-bit counter
is designed to count seconds and can be used to
derive time-of-day, week, month, month, and
year by using a software algorithm. A precision,
temperature-compensated reference and
comparator circuit monitors the status of VCC.
When an out-of-tolerance condition occurs, an
internal power-fail signal is generated that forces
the reset to the active state. When VCC returns to
an in-tolerance condition, the reset signal is kept
in the active state for a period of time to allow
the power supply and processor to stabilize.
FEATURES 32-Bit Counter I2C Serial Interface Automatic Power-Fail Detect and Switch
Circuitry Power-Fail Reset Output Low-Voltage Oscillator Operation
(1.3V min) Trickle-Charge Capability Underwriters Laboratories (UL) Recognized -40°C to +85°C Operating Range
PIN CONFIGURATION
TYPICAL OPERATING CIRCUIT
PDIP
SO µSOP
TOP VIEW
VCC
RST
SCL
SDA
X1
X2
VBACKUP
GND
DS1672
DS1672 2C 32-Bit Binary Counter RTC 19-6032; Rev 9/11
DS1672
ORDERING INFORMATION
PART TEMP RANGE VOLTAGE (V) PIN-PACKAGE TOP MARK* DS1672-2+ -40°C to +85°C 2.0 8 PDIP (300 mils) DS1672-2
DS1672-3+ -40°C to +85°C 3.0 8 PDIP (300 mils) DS1672-3
DS1672-33+ -40°C to +85°C 3.3 8 PDIP (300 mils) DS1672-33
DS1672S-2+ -40°C to +85°C 2.0 8 SO (150 mils) D1672-2
DS1672S-3+ -40°C to +85°C 3.0 8 SO (150 mils) D1672-3
DS1672S-33+ -40°C to +85°C 3.3 8 SO (150 mils) D167233
DS1672S-3+T&R -40°C to +85°C 3.0 8 SO (150 mils)/Tape
and Reel D1672-3
DS1672S-33+T&R -40°C to +85°C 3.3 8 SO (150 mils)/Tape
and Reel D167233
DS1672U-2+ -40°C to +85°C 2.0 8 µSOP(3mm) 1672
rr -2
DS1672U-3+ -40°C to +85°C 3.0 8 µSOP(3mm) 1672
rr -3
DS1672U-33+ -40°C to +85°C 3.3 8 µSOP(3mm) 1672
rr -33
DS1672U-33+T&R -40°C to +85°C 3.3 8 µSOP(3mm)/Tape
and Reel
1672
rr -33
+ Denotes a lead-free/RoHS-compliant device.
* A “+” anywhere on the top mark denotes a lead-free device. rr = 2-digit alphanumeric revision code.
DS1672
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Pin Relative to Ground……………………………………………..-0.5V to +6.0V
Operating Temperature Range (noncondensing) ...…………………………………………-40°C to +85°C
Storage Temperature Range……………………………………………………………….-55°C to +125°C
Soldering Temperature (reflow)………………………………………….…………………. +260°C
Lead Temperature (soldering, 10s) ……………………………………………………………….. +260°C
This is a stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time can affect device
reliability.
RECOMMENDED OPERATING CONDITIONS
(TA = -40°C to +85°C) (Note 1)
PARAMETER SYMBOL MIN TYP MAX UNITS
Supply
Voltage
DS1672-2 VCC 1.8 2.0 5.5 DS1672-3 VCC 2.7 3.0 5.5
DS1672-33 VCC 2.97 3.3 5.5
Logic 1 VIH 0.7 x VCC VCC + 0.5 V
Logic 0 VIL -0.5 +0.3 x VCC V
Backup Supply Voltage VBACKUP 1.3 3.0 3.63 V
Note 1: All voltages referenced to ground.
DC ELECTRICAL CHARACTERISTICS
(VCCMIN < VCC < VCCMAX, TA = -40°C to +85°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Active Supply Current
(Note 2)
ICCA -2: VCC = 2.2V 600 μA
-3: VCC = 3.3V
-33: VCC = 3.63V
Standby Current
(Note 3)
ICCS -2: VCC = 2.2V 500 μA
-3: VCC = 3.3V
-33: VCC = 3.63V
Power-Fail Voltage VPF -2: 2.70 2.88 2.97 V
-3: 2.45 2.60 2.70
-33: 1.58 1.70 1.80
VBACKUP Leakage Current IBACKUPLKG 25 50 nA
Logic 0 Output (Note 4) IOL VOL = 0.4V 3 mA
Logic 0 Output (Note 4,
DS1672-2 Only)
IOL VCC > 2V; VOL = 0.4V 3 mA
VCC < 2V; VOL = VCC
* 0.2
Note 1: All voltages referenced to ground.
Note 2: ICCA specified with SCL clocking at max frequency (400kHz), trickle charger disabled.
Note 3: ICCS specified with VCC = VCCTYP and SDA, SCL = VCCTYP, trickle charger disabled.
Note 4: SDA and RST.
DS1672
DC ELECTRICAL CHARACTERISTICS
(VCC = 0V, TA = -40°C to +85°C.) (Note 5)
PARAMETER SYMBOL MIN TYP MAX UNITS
VBACKUP Current (Oscillator On) IBACKUPOSC 0.425 1 µA
VBACKUP Current (Oscillator Off) IBACKUP 200 nA
Note 5: Using the recommended crystal on X1 and X2.
CRYSTAL SPECIFICATIONS*
PARAMETER SYMBOL MIN TYP MAX UNITS
Nominal Frequency fO 32.768 kHz
Series Resistance ESR 45 kΩ
Load Capacitance CL 6 pF
*The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58: Crystal
Considerations for Dallas Real-Time Clocks for additional specifications
DS1672
AC ELECTRICAL CHARACTERISTICS
(VCC = 0V, TA = -40°C to +85°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL Clock
Frequency fSCL
Fast mode 100 400
kHz
Standard mode 100
Bus Free Time
Between a STOP and
START Condition
tBUF
Fast mode 1.3 µs Standard mode 4.7
Hold Time
(Repeated) START
Condition (Note 6)
tHD:STA
Fast mode 0.6 µs Standard mode 4.0
LOW Period of SCL
Clock tLOW
Fast mode 1.3 µs Standard mode 4.7
HIGH Period of SCL
Clock tHIGH Fast mode 0.6 µs Standard mode 4.0
Setup Time for a
Repeated START
Condition
tSU:STA
Fast mode 0.6 µs Standard mode 4.7
Data Hold Time
(Notes 7, 8) tHD:DAT Fast mode 0 0.9 µs
Standard mode 0
Data Setup Time
(Note 9) tSU:DAT Fast mode 100 ns Standard mode 250
Rise Time of Both
SDA and SCL
Signals (Note 10)
tR
Fast mode 20 + 0.1CB 300
ns Standard mode 1000
Fall Time of Both
SDA and SCL
Signals (Note 10)
tF
Fast mode 20 + 0.1CB 300
ns
Standard mode 300
Setup Time for STOP
Condition tSU:STO
Fast mode 0.6 µs Standard mode 4.0
Capacitive Load for
Each Bus Line
(Note 10)
CB 400 pF
I/O Capacitance CI/O 10 pF
Note 6: After this period, the first clock pulse is generated.
Note 7: A device must internally provide a hold time of at least 300ns for the SDA signal (referenced to the VIHMIN of the SCL signal) in
order to bridge the undefined region of the falling edge of SCL.
Note 8:The maximum tHD:DAT has 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 ≥ to 250ns must then be met. This will
automatically be 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.
DS1672
POWER-UP/POWER-DOWN CHARACTERISTICS
(TA = -40°C to +85°C)
PARAMETER SYMBOL MIN TYP MAX UNITS
VCC Detect to RST (VCC Falling) tRPD 10 μs
VCC Detect to RST (VCC Rising)
(Note 11) tRPU 250 ms
VCC Fall Time; VPF(MAX) to VPF(MIN) tF 300 µs
VCC Rise Time; VPF(MIN) to VPF(MAX) tR 0 µs
Note 11: If the EOSC bit in the control register is set to logic 1, tRPU is equal to 250ms plus the startup time of the crystal oscillator.
Warning: Negative undershoots below –0.3V while the part is in battery-backed mode can cause
loss of data.
Figure 1. Timing Diagram
SCL
START
SDA
STOP
tBUF
REPEATED
START
tHD:STAtLOW
tHD:STA
tHD:DATtSU:DATtHIGH
tSU:STA
tSU:STO
Figure 2. Power-Up/Power-Down Timing
OUTPUTS
VCC VPF(max)
INPUTS
HIGH IMPEDANCE
RST
DON'T CARE
VALID
RECOGNIZED RECOGNIZED
VALID
tRPD
VPF(min)
tF
tPD
tR
tRPU
DS1672
PIN DESCRIPTION
PIN NAME FUNCTION
1, 2 X1, X2
Connections for Standard 32.768kHz Quartz Crystal. The internal oscillator
circuitry is designed for operation with a crystal having a specified load
capacitance (CL) of 6pF. For more information about crystal selection and
crystal layout considerations, refer to Application Note 58: Crystal
Considerations with Dallas Real-Time Clocks. The DS1672 can also be driven
by an external 32.768kHz oscillator. In this configuration, the X1 pin is
connected to the external oscillator signal and the X2 pin is left unconnected. VBACKUP
Battery Input for Any Standard 3V Lithium Cell or Other Energy Source.
Battery voltage must be held between 1.3V and 3.63V for proper operation.
Diodes placed in series between the power source and the VBACKUP pin may
result in improper operation. If a backup supply is not required, VBACKUP must
be grounded. UL recognized to ensure against reverse charging current when
used in conjunction with a lithium battery (charger disabled). See “Conditions
of Acceptability” at /qa/info/ul. GND Ground. SDA Serial-Data Input/Output. SDA is the input/output pin for the I2C serial
interface. The SDA pin is open drain and requires an external pullup resistor. SCL I2C Serial-Clock Input. SCL is used to synchronize data movement on the
serial interface and requires an external pullup resistor. RST Active-Low Reset Output. It functions as a microprocessor reset signal. This
pin is an open-drain output and requires an external pullup resistor. VCC
Power pin for Primary Power Supply. When VCC is applied within normal
limits, the device is fully accessible and data can be written and read. When
VCC is below VPF, reads and writes are inhibited. Figure 3. Recommended Layout for Crystal
LOCAL GROUND PLANE (LAYER 2)
CRYSTAL
X1
X2
GND
DS1672
Detailed Description
The DS1672 provides a 32-bit counter that increments once-per-second. The counter data is accessible
via an I2C serial interface. A precision, temperature-compensated, voltage reference and comparator
circuit monitors VCC. When VCC drops below VPF, RST becomes active and the interface is disabled to
prevent data corruption. The device switches to the backup supply input, which maintains oscillator and
counter operation while VCC is absent. When VCC rises above VPF, RST remains low for a period of time
(tRPU) to allow VCC to stabilize.
The block diagram in Figure 4 shows the main elements of the DS1672. As shown, communications to
and from the DS1672 occur serially over a I2C, bidirectional bus. The DS1672 operates as a slave device
on the I2C bus. Access is obtained by implementing a START condition and providing a device
identification code followed by a register address. Subsequent registers can be accessed sequentially until
a STOP condition is executed.
Figure 4. Block Diagram
Oscillator Circuit
The DS1672 uses an external 32.768kHz crystal. The oscillator circuit does not require any external
resistors or capacitors to operate. Table 1 specifies several crystal parameters for the external crystal.
Figure 4 shows a functional schematic of the oscillator circuit. If using a crystal with the specified
characteristics, the startup time is usually less than one second.
Table 1. Crystal Specifications*
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Nominal Frequency FO 32.768 kHz
Series Resistance ESR 45 kΩ
Load Capacitance CL 6 pF
* The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58:
Clock Accuracy
32-Bit Counter
(4 Bytes)2C Interface
Power Control
Address Register
Control Logic
1HzCCBACKUP
GND
SCL
SDA
Control
Trickle ChargerX2
RST
Dallas
Semiconductor
DS1672CL
Oscillator
and
divider
