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DS1391
Low-Voltage SPI/3-Wire RTCs with Trickle Charger
General Description
The low-voltage serial-peripheral interface (SPI™)
DS1390/DS1391 and the low-voltage 3-wire DS1392/
DS1393 real-time clocks (RTCs) are clocks/calendars
that provide hundredths of a second, seconds, min-
utes, 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.
One programmable time-of-day alarm is provided. A
temperature-compensated voltage reference monitors
the status of VCCand automatically switches to the
backup supply if a power failure is detected. On the
DS1390, a single open-drain output provides a CPU
interrupt or a square wave at one of four selectable fre-
quencies. The DS1391 replaces the SQW/INTpin with aRSToutput/debounced input.
The DS1390 and DS1391 are programmed serially
through an SPI-compatible, bidirectional bus. The
DS1392 and DS1393 communicate over a 3-wire serial
bus, and the extra pin is used for either a separate
interrupt pin or a RSToutput/debounced input.
All four devices are available in a 10-pin µSOP package,
and are rated over the industrial temperature range.
Applications
Hand-Held Devices
GPS/Telematics Devices
Embedded Time Stamping
Medical Devices
FeaturesReal-Time Clock Counts Hundredths of Seconds,
Seconds, Minutes, Hours, Day, Date, Month, and
Year with Leap-Year Compensation Valid Up to
2100Output Pin Configurable as Interrupt or Square
Wave with Programmable Frequency of
32.768kHz, 8.192kHz, 4.096kHz, or 1Hz
(DS1390/DS1393 Only)One Time-of-Day AlarmPower-Fail Detect and Switch CircuitryReset Output/Debounced Input (DS1391/DS1393)Separate SQW and INT Output (DS1392)Trickle-Charge CapabilitySPI Supports Modes 1 and 3 (DS1390/DS1391)3-Wire Interface (DS1392/DS1393)4MHz at 3.0V and 3.3V1MHz at 1.8VThree Operating Voltages: 1.8V ±5%, 3.0V ±10%,
and 2.97 to 5.5VIndustrial Temperature Range: -40°C to +85°CUnderwriters Laboratory (UL) Recognized
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Ordering Information
Rev 0; 7/04
Typical Operating Circuits and Pin Configurations appear at
end of the data sheet.
Where “rr”is a revision code on the second line of the top mark.
SPI is a trademark of Motorola, Inc.
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
ABSOLUTE MAXIMUM RATINGS
RECOMMENDED DC OPERATING CONDITIONS
(VCC= VCC(MIN)to VCC(MAX), TA= -40°C to +85°C, unless otherwise noted. Typical values are at nominal supply voltage and TA= +25°C,
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 VCCPin Relative to Ground.....-0.3V to +6.0V
Voltage Range on Inputs Relative
to Ground...............................................-0.3V to (VCC+ 0.3V)
Operating Temperature Range...........................-40°C to +85°C
Storage Temperature Range.............................-55°C to +125°C
Soldering Temperature.......................................See IPC/JEDEC
J-STD-020A Specification
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
RECOMMENDED DC OPERATING CONDITIONS (continued)
(VCC= VCC(MIN)to VCC(MAX), TA= -40°C to +85°C, unless otherwise noted. Typical values are at nominal supply voltage and TA= +25°C,
DC ELECTRICAL CHARACTERISTICS
AC ELECTRICAL CHARACTERISTICS—SPI INTERFACE
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Figure 1. Timing Diagram—SPI Read Transfer
Figure 2. Timing Diagram—SPI Write Transfer
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
AC ELECTRICAL CHARACTERISTICS—3-WIRE INTERFACE
AC ELECTRICAL CHARACTERISTICS
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Figure 3. Timing Diagram—3-Wire Read Transfer
Figure 4. Timing Diagram—3-Wire Write Transfer
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Figure 5. Power-Up/Down Timing
Figure 6. Pushbutton Reset Timing
POWER-UP/POWER-DOWN CHARACTERISTICS
(TA= -40°C to +85°C) (Figures 5, 6)
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
CAPACITANCE
WARNING:Under no circumstances are negative undershoots, of any amplitude, allowed when the device
is in write protection.
Note 1: Limits at -40°C are guaranteed by design and not production tested.
Note 2:All voltages are referenced to ground.
Note 3:The use of the 250Ωtrickle-charge resistor is not allowed at VCC > 3.63V and should not be enabled. Use of the diode is
not recommended for VCC< 3.0V.
Note 4:Measured at VCC= typ, VBACKUP= 0V, register 0Fh = A5h.
Note 5:Measured at VCC= typ, VBACKUP= 0V, register 0Fh = A6h.
Note 6:Measured at VCC= typ, VBACKUP= 0V, register 0Fh = A7h.
Note 7:SCLK, DIN, CSon DS1390/DS1391; SCLK, and CE on DS1392/DS1393.
Note 8:DOUT, SQW/INT(DS1390/DS1393), SQW, and INT(DS1392).
Note 9:The RST pin has an internal 50kΩ(typ) pullup resistor to VCC.
Note 10: ICCA—SCLK clocking at max frequency = 4MHz for 3V and 3.3V versions; 1MHz for 1.8V version; RST (DS1391/DS1393)
inactive. Outputs are open.
Note 11:Specified with bus inactive.
Note 12:Measured with a 32.768kHz crystal attached to X1 and X2. Typical values measured at +25°C and 3.0VBACKUP.
Note 13:With 50pF load.
Note 14:Measured at VIH= 0.7 x VDDor VIL= 0.2 x VDD, 10ns rise/fall times.
Note 15:Measured at VOH= 0.7 x VDDor VOL= 0.2 x VDD. Measured from the 50% point of SCLK to the VOHminimum of SDO.
Note 16:The parameter tOSFis the time that the oscillator must be stopped for the OSF flag to be set over the voltage range of
0 ≤VCC≤VCC(MAX)and 1.3V ≤VBAT≤5.5V.
Note 17:This delay applies only if the oscillator is enabled and running. If the EOSCbit is 1, the startup time of the oscillator is
added to this delay.
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Typical Operating Characteristics
(VCC= +3.3V, TA= +25°C, unless otherwise noted.)
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Pin Description
Detailed Description
The DS1390/DS1391/DS1392/DS1393 RTCs are low-
power clocks/calendars with alarms. Address and data
are transferred serially through a 4-wire SPI interface
for the DS1390 and DS1391 and through a 3-wire inter-
face for the DS1392 and DS1393. The clocks/calendars
provide hundredths of seconds, seconds, minutes,
hours, day, date, month, and year information. The
alarm functions are performed off all timekeeping regis-
ters, allowing the user to set high resolution alarms. The
date at the end of the month is automatically adjusted
for months with fewer than 31 days, including correc-
tions for leap year. The clocks operate in either the 24-
hour or 12-hour format with an AM/PM indicator. All four
devices have a built-in temperature-compensated volt-
age reference that detects power failures and automati-
cally switches to the battery supply. Additionally, the
devices can provide trickle charging of the backup
voltage source, with selectable charging resistance
and diode voltage drops.
Operation
The DS1390/DS1391 operate as a slave device on the
SPI serial bus. The DS1392/DS1393 operate using a
3-wire synchronous serial bus. Access is obtained by
selecting the part by the CSpin (CE on DS1392/
DS1393) and clocking data into/out of the part using
the SCLK and DIN/DOUT pins (I/O on DS1392/
DS1393). Multiple-byte transfers are supported within
one CSlow period (see the SPI Serial-Data Bussec-
tion). The devices are fully accessible and data can be
written and read when VCCis greater than VPF.
DS1390/DS1391/DS1392/DS1393
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Functional Diagram
DS1390/DS1391/DS1392/DS1393
However, when VCCfalls below VPF, the internal clock
registers are blocked from any access. If VPFis less
than VBACKUP, the device power is switched from VCC
to VBACKUPwhen VCCdrops below VPF. If VPFis
greater than VBACKUP, the device power is switched
from VCCto VBACKUPwhen VCCdrops below
VBACKUP. The registers are maintained from the
VBACKUPsource until VCCis returned to nominal levels.
See the Functional Diagramfor the main elements of
these serial RTCs.
Oscillator Circuit
All four devices use an external 32.768kHz crystal. The
oscillator circuit does not require any external resistors
or capacitors to operate. Table1 specifies several crys-
tal parameters for the external crystal, and Figure7
shows a functional schematic of the oscillator circuit. If
a crystal is used with the specified characteristics, the
startup time is usually less than one second.
Clock Accuracy
The accuracy of the clock is dependent upon the accu-
racy of the crystal and the accuracy of the match
between the capacitive load of the oscillator circuit and
the capacitive load for which the crystal was trimmed.
Additional error is added by crystal frequency drift
caused by temperature shifts. External circuit noise
coupled into the oscillator circuit can result in the clock
running fast. Figure8 shows a typical PC board layout
for isolation of the crystal and oscillator from noise.
Refer to Application Note 58: Crystal Considerations
with Dallas Real-Time Clocksfor detailed information.
Low-Voltage SPI/3-Wire RTCs withrickle Charger
Figure 7. Oscillator Circuit Showing Internal Bias Network

Partno	Mfg	Dc	Qty	Available	Descript
DS1391	MAX	N/a	2	avai	Low-Voltage SPI/3-Wire RTCs with Trickle Charger