Maxim DS1340C-18 I2c rtc with trickle charger Datasheet

DS1340
I2C RTC with Trickle Charger
General Description
Features
The DS1340 is a real-time clock (RTC)/calendar that is
pin compatible and functionally equivalent to the ST
M41T00, including the software clock calibration. The
device additionally provides trickle-charge capability
on the VBACKUP pin, a lower timekeeping voltage, and
an oscillator STOP flag. Block access of the register
map is identical to the ST device. Two additional registers, which are accessed individually, are required for
the trickle charger and flag. The clock/calendar provides seconds, minutes, hours, day, date, month, and
year information. A built-in power-sense circuit detects
power failures and automatically switches to the backup supply. Reads and writes are inhibited while the
clock continues to run. The device is programmed serially through an I2C bidirectional bus.
♦ Enhanced Second Source for the ST M41T00
♦ Available in a Surface-Mount Package with an
Integrated Crystal (DS1340C)
♦ Fast (400kHz) I2C Interface
♦ Software Clock Calibration
♦ RTC Counts Seconds, Minutes, Hours, Day, Date,
Month, and Year
♦ Automatic Power-Fail Detect and Switch Circuitry
♦ Trickle-Charge Capability
♦ Low Timekeeping Voltage Down to 1.3V
♦ Three Operating Voltage Ranges (1.8V, 3V, and 3.3V)
♦ Oscillator Stop Flag
♦ Available in 8-Pin µSOP or SO Packages
♦ Underwriters Laboratories (UL) Recognized
Applications
Ordering Information
Portable Instruments
Point-of-Sale Equipment
PART
TEMP RANGE
PINPACKAGE
TOP MARK†
DS1340Z-18+
-40°C to +85°C
8 SO
(0.150in)
D1340-18
DS1340Z-3+
-40°C to +85°C
8 SO
(0.150in)
DS1340-3
DS1340Z-33+
-40°C to +85°C
8 SO
(0.150in)
D134033
DS1340U-18+
-40°C to +85°C 8 μSOP
DS1340U-3+
-40°C to +85°C 8 μSOP
1340 -3
DS1340U-33+
-40°C to +85°C 8 μSOP
1340 -33
Medical Equipment
Telecommunications
Typical Operating Circuit
VCC
VCC
CRYSTAL
VCC
RPU
RPU
1
X1
2
X2
6 SCL
CPU
C1
8
VCC
FT/OUT
7
RPU = tR / CB
VBACKUP
GND
4
DS1340C-18#
-40°C to +85°C 16 SO
DS1340C-18
DS1340C-3#
-40°C to +85°C 16 SO
DS1340C-3
DS1340C-33#
-40°C to +85°C 16 SO
DS1340C-33
+Denotes a lead(Pb)-free/RoHS-compliant package.
DS1340
5 SDA
1340 -18
3
#Denotes a RoHS-compliant device that may include lead(Pb)
that is exempt under RoHS requirements. The 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 a lead(Pb)-free device.
A "#" denotes a RoHS-compliant device.
Pin Configurations appear at end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim Direct at
1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
19-5578; Rev 8; 4/13
DS1340
I2C RTC with Trickle Charger
ABSOLUTE MAXIMUM RATINGS
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-55°C to +125°C
Lead Temperature (soldering, 10s) .................................+260°C
Soldering Temperature (reflow) .......................................+260°C
Voltage Range on VCC or VBACKUP Pins
Relative to Ground.............................................-0.3V to +6.0V
Voltage Range on SDA, SCL, and FT/OUT
Relative to Ground..................................-0.3V to (VCC + 0.3V)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED DC OPERATING CONDITIONS
(VCC = VCC MIN to VCC MAX, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VCC = 3.3V, TA = +25°C, unless
otherwise noted.) (Note 1)
PARAMETER
SYMBOL
MIN
TYP
MAX
DS1340-18
CONDITIONS
1.71
1.8
5.5
2.7
3.0
5.5
2.97
3.3
Supply Voltage (Note 2)
VCC
DS1340-3
Input Logic 1 (SDA, SCL)
VIH
(Note 2)
Input Logic 0 (SDA, SCL)
VIL
(Note 2)
Supply Voltage, Pullup
(FT/OUT, SDA, SCL), VCC = 0V
VPU
(Note 2)
DS1340-33
Backup Supply Voltage (Note 2)
Trickle-Charge Current-Limiting
Resistors
VBACKUP
DS1340-18
1.3
3.7
DS1340-3
1.3
3.7
DS1340-33
1.3
2000
I/O Leakage (SDA, FT/OUT)
ILO
SDA Logic 0 Output
I OLSDA
FT/OUT Logic 0 Output
I OLSQW
ICCA
ICCS
(Note 6)
V
4000
DS1340-18
1.51
1.6
1.71
DS1340-3
2.45
2.6
2.7
DS1340-33
2.70
2.88
2.97
-1
-1
V
+1
μA
+1
μA
VCC > 2V; VOL = 0.4V
3.0
1.7V < VCC < 2V; VOL = 0.2 x VCC
VCC > 2V; VOL = 0.4V
3.0
3.0
1.7V < VCC < 2V; VOL = 0.2 x VCC
3.0
1.3V < VCC < 1.7V; VOL = 0.2x VCC
DS1340-18; VCC = 1.89V
250
72
150
DS1340-3; VCC = 3.3V
108
200
DS1340-33; VCC = 5.5V
192
300
DS1340-18; VCC = 1.89V
60
100
DS1340-3; VCC = 3.3V
81
125
DS1340-33; VCC = 5.5V
100
150
IBACKUPLKG VBACKUP = 3.7V
V
5.5
(Note 5)
ILI
2
5.5
R2
Input Leakage (SCL, CLK)
VBACKUP Leakage Current
V
250
VPF
Standby Current (Note 8)
V
+0.3 x VCC
(Notes 3, 4)
Power-Fail Voltage (Note 2)
Active Supply Current (Note 7)
VCC + 0.3
R1
R3
V
5.5
0.7 x VCC
-0.3
UNITS
100
mA
mA
μA
μA
μA
nA
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
DC ELECTRICAL CHARACTERISTICS
(VCC = 0V, VBACKUP = 3.7V, TA = -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
VBACKUP Current
VBACKUP Data-Retention Current
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
IBACKUP1
OSC ON, FT = 0 (Note 9)
800
1150
IBACKUP2
OSC ON, FT = 1 (Note 9)
850
1250
IBACKUP3
OSC ON, FT = 0, VBACKUP = 3.0V,
TA = +25°C (Notes 9, 10)
800
1000
25.0
100
nA
TYP
MAX
UNITS
IBACKUPDR OSC OFF
nA
AC ELECTRICAL CHARACTERISTICS
(VCC = VCC MIN to VCC MAX, TA = -40°C to +85°C, unless otherwise noted.) (Notes 1,14, Figure 1)
PARAMETER
SYMBOL
SCL Clock Frequency
f SCL
Bus Free Time Between STOP
and START Conditions
tBUF
Hold Time (Repeated) START
Condition (Note 11)
tHD:STA
Low Period of SCL Clock
tLOW
High Period of SCL Clock
tHIGH
Data Hold Time (Notes 12, 13)
tHD:DAT
Data Setup Time (Note 14)
t SU:DAT
START Setup Time
t SU:STA
Rise Time of SDA and SCL
Signals (Note 15)
tR
Fall Time of SDA and SCL
Signals (Note 15)
tF
Setup Time for STOP Condition
t SU:STO
Capacitive Load for Each Bus
Line
CB
I/O Capacitance (SCL, SDA)
CI/O
Pulse Width of Spikes that Must
be Suppressed by the Input
Filter
t SP
Oscillator Stop Flag (OSF) Delay
t OSF
Maxim Integrated
CONDITIONS
Standard mode
MIN
0
100
Fast mode
100
400
Standard mode
4.7
Fast mode
1.3
Standard mode
4.0
Fast mode
0.6
Standard mode
4.7
Fast mode
1.3
Standard mode
4.0
Fast mode
0.6
μs
μs
μs
μs
Standard mode
0
0.9
Fast mode
0
0.9
Standard mode
250
Fast mode
100
Standard mode
4.7
Fast mode
0.6
μs
20 + 0.1CB
1000
Fast mode
20 + 0.1CB
300
Standard mode
20 + 0.1CB
20 + 0.1CB
300
Standard mode
4.7
Fast mode
0.6
μs
ns
Standard mode
Fast mode
kHz
300
ns
ns
μs
(Note 15)
400
pF
10
pF
Fast mode
30
ns
(Note 16)
100
ms
3
DS1340
I2C RTC with Trickle Charger
POWER-UP/POWER-DOWN CHARACTERISTICS
(TA = -40°C to +85°C) (Figure 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
(Note 17)
MAX
UNITS
2
ms
Recovery at Power-Up
tREC
VCC Fall Time; VPF(MAX) to
VPF(MIN)
tVCCF
300
µs
VCC Rise Time; VPF(MIN) to
VPF(MAX)
tVCCR
0
µs
WARNING: Under no circumstances are negative undershoots, of any amplitude, allowed when device is in battery-backup mode.
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
Note 15:
Note 16:
Note 17:
Limits at -40°C are guaranteed by design and not production tested.
All voltages are referenced to ground.
Measured at VCC = typ, VBACKUP = 0V, register 08h = A5h.
The use of the 250Ω trickle-charge resistor is not allowed at VCC > 3.63V and should not be enabled.
Measured at VCC = typ, VBACKUP = 0V, register 08h = A6h.
Measured at VCC = typ, VBACKUP = 0V, register 08h = A7h.
ICCA—SCL clocking at max frequency = 400kHz.
Specified with I2C bus inactive.
Measured with a 32.768kHz crystal attached to the X1 and X2 pins.
Limits at +25°C are guaranteed by design and not production tested.
After this period, the first clock pulse is generated.
A device must internally provide a hold time of at least 300ns for the SDA signal (referred to as the VIH(MIN) of the SCL
signal) to bridge the undefined region of the falling edge of SCL.
The maximum tHD:DAT only has to be met if the device does not stretch the low period (tLOW) of the SCL signal.
A fast-mode device can be used in a standard-mode system, but the requirement tSU:DAT ≥ to 250ns must be met. This
is automatically the case if the device does not stretch the low period of the SCL signal. If such a device does stretch the
low period of the SCL signal, it must output the next data bit to the SDA line tR MAX + tSU:DAT = 1000 + 250 = 1250ns
before the SCL line is released.
CB—total capacitance of one bus line in pF.
The parameter tOSF is the period of time the oscillator must be stopped for the OSF flag to be set over the 0V ≤ VCC ≤
VCCMAX and 1.3V ≤ VBAT ≤ 3.7V range.
This delay applies only if the oscillator is enabled and running. If the oscillator is disabled or stopped, no power-up delay
occurs.
SDA
tBUF
tF
tHD:STA
tLOW
tSP
SCL
tHIGH
tHD:STA
tHD:DAT
STOP
tSU:STA
tR
START
tSU:STO
tSU:DAT
REPEATED
START
NOTE: TIMING IS REFERENCED TO VIL(MAX) AND VIH(MIN).
Figure 1. Data Transfer on I2C Serial Bus
4
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
VCC
VPF(MAX)
VPF
VPF(MIN)
VPF
tR
tF
tREC
INPUTS
RECOGNIZED
DON'T CARE
RECOGNIZED
HIGH-Z
OUTPUTS
VALID
VALID
Figure 2. Power-Up/Power-Down Timing
Typical Operating Characteristics
(VCC = +3.3V, TA = +25°C, unless otherwise noted.)
100
800
-3.3V
SUPPLY CURRENT (nA)
150
850
DS1340 toc02
DS1340 toc01
125
SUPPLY CURRENT (μA)
SUPPLY CURRENT (μA)
200
IBACKUP1 (FT = 0) vs. VBACKUP
ICCS vs. VCC FT = 0
150
100
-3.0V
75
DS1340 toc03
ICCSA vs. VCC FT = 0
250
-1.8V
50
750
700
650
600
550
500
50
25
450
0
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
VCC (V)
VCC (V)
VBACKUP (V)
IBACKUP2 (FT = 1) vs. VBACKUP
IBACKUP3 vs. TEMPERATURE
OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE
(FT x 64)
850
VBACKUP = 3.0V
32768.6
32768.5
800
700
650
600
550
500
750
FREQUENCY (Hz)
SUPPLY CURRENT (nA)
750
700
650
400
VBACKUP (V)
Maxim Integrated
32768.3
32768.2
32768.1
32768.0
500
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
32768.4
600
550
450
DS1340 toc06
800
DS1340 toc05
DS1340 toc04
850
SUPPLY CURRENT (nA)
400
0
-40
-20
0
20
40
TEMPERATURE (°C)
60
80
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
VBACKUP (V)
5
DS1340
I2C RTC with Trickle Charger
Pin Description
PIN
NAME
8
16
1
—
X1
2
—
X2
FUNCTION
Connections for a Standard 32.768kHz Quartz Crystal. The internal oscillator circuitry is designed for
operation with a crystal having a specified load capacitance (CL) of 12.5pF. X1 is the input to the
oscillator and can optionally be connected to an external 32.768kHz oscillator. The output of the
internal oscillator, X2, is left unconnected if an external oscillator is connected to X1.
Connection for a Secondary Power Supply. For the 1.8V and 3V devices, VBACKUP must be held
between 1.3V and 3.7V for proper operation. Diodes placed in series between the supply and the input
pin may result in improper operation. VBACKUP can be as high as 5.5V on the 3.3V device.
VBACKUP This pin can be connected to a primary cell such as a lithium coin cell. Additionally, this pin can be
connected to a rechargeable cell or a super cap when used with the trickle-charge feature. UL
recognized to ensure against reverse charging when used with a lithium battery
(www.maximintegrated.com/qa/info/ul).
3
14
4
15
GND
Ground
5
16
SDA
Serial Data Input/Output. SDA is the data input/output for the I2C serial interface. The SDA pin is open
drain and requires an external pullup resistor.
6
1
SCL
Serial Clock Input. SCL is the clock input for the I2C interface and is used to synchronize data
movement on the serial interface.
7
2
FT/OUT
Frequency Test/Output. This pin is used to output either a 512Hz signal or the value of the OUT bit.
When the FT bit is logic 1, the FT/OUT pin toggles at a 512Hz rate. When the FT bit is logic 0, the
FT/OUT pin reflects the value of the OUT bit. This open-drain pin requires an external pullup resistor,
and operates with either VCC or VBACKUP applied. The pullup voltage can be up to 5.5V, regardless of
the voltage on VCC. If not used, this pin can be left unconnected.
8
3
VCC
Primary Power Supply. When voltage is applied within normal limits, the device is fully accessible and
data can be written and read. When a backup supply is connected to the device and VCC is below VPF,
reads and writes are inhibited. However, the timekeeping function continues unaffected by the lower
input voltage.
—
4–13
N.C.
No Connection. Must be connected to ground.
Detailed Description
The DS1340 is a low-power clock/calendar with a trickle
charger. Address and data are transferred serially
through a I2C bidirectional bus. 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 DS1340
has a built-in power-sense circuit that detects power failures and automatically switches to the backup supply.
Power Control
The power-control function is provided by a precise,
temperature-compensated voltage reference and a
comparator circuit that monitors the V CC level. The
device is fully accessible and data can be written and
read when VCC is greater than VPF. However, when VCC
falls below VPF, the internal clock registers are blocked
6
from any access. If V PF is less than V BACKUP , the
device power is switched from VCC to VBACKUP when
VCC drops below VPF. If VPF is greater than VBACKUP,
the device power is switched from VCC to VBACKUP
Table 1. Power Control
SUPPLY CONDITION
READ/WRITE
ACCESS
POWERED
BY
VCC < V PF,
VCC < VBACKUP
No
VBAT
VCC < V PF,
VCC > VBACKUP
No
VCC
VCC > V PF,
VCC < VBACKUP
Yes
VCC
VCC > V PF,
VCC > VBACKUP
Yes
VCC
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
when VCC drops below VBACKUP. The registers are
maintained from the V BACKUP source until V CC is
returned to nominal levels (Table 1). After VCC returns
above VPF, read and write access is allowed tREC.
the crystal and oscillator from noise. Refer to
Application Note 58: Crystal Considerations with Dallas
Real-Time Clocks (www.maximintegrated.com/RTCapps)
for detailed information.
Oscillator Circuit
DS1340C Only
The DS1340 uses an external 32.768kHz crystal. The
oscillator circuit does not require any external resistors
or capacitors to operate. Table 2 specifies several crystal parameters for the external crystal. Figure 3 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.
The DS1340C integrates a standard 32,768Hz crystal
into the package. Typical accuracy with nominal VCC
and +25°C is approximately +15ppm. Refer to
Application Note 58 for information about crystal accuracy vs. temperature.
Clock Accuracy
The initial clock accuracy depends on the accuracy 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.
Figure 4 shows a typical PC board layout for isolating
Table 2. Crystal Specifications*
PARAMETER
Nominal
Frequency
Series Resistance
Load Capacitance
SYMBOL
MIN
TYP
fO
32.768
ESR
CL
12.5
MAX
UNITS
kHz
80
Operation
The DS1340 operates as a slave device on the serial
bus. Access is obtained by implementing a START
condition and providing a device identification code followed by data. Subsequent registers can be accessed
sequentially until a STOP condition is executed. The
device is fully accessible and data can be written and
read when VCC is greater than VPF. However, when
VCC falls below VPF, the internal clock registers are
blocked from any access. If VPF is less than VBACKUP,
the device power is switched from VCC to VBACKUP
when V CC drops below V PF . If V PF is greater than
VBACKUP, the device power is switched from VCC to
VBACKUP when VCC drops below VBACKUP. The registers are maintained from the VBACKUP source until VCC
is returned to nominal levels. The functional diagram
(Figure 5) shows the main elements of the serial RTC.
kΩ
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.
LOCAL GROUND PLANE (LAYER 2)
X1
RTC
CRYSTAL
X2
COUNTDOWN
CHAIN
CL1
C L2
RTC
REGISTERS
GND
X2
X1
CRYSTAL
Figure 4. Layout Example
Figure 3. Oscillator Circuit Showing Internal Bias Network
Maxim Integrated
7
DS1340
I2C RTC with Trickle Charger
X1
FT/OUT
CL
CL
X2
512Hz
32,768Hz
MUX/
BUFFER
DIVIDER AND
CALIBRATION
CIRCUIT
"C" VERSION ONLY
1Hz
VCC
CLOCK AND
CALENDAR
REGISTERS
POWER
CONTROL
VBACKUP
N
CONTROL
LOGIC
SERIAL
INTERFACE
AND ADDRESS
REGISTER
SCL
SDA
USER BUFFER
(7 BYTES)
DS1340
Figure 5. Functional Diagram
Address Map
Table 3 shows the DS1340 address map. The RTC registers are located in address locations 00h to 06h, and
the control register is located at 07h. The trickle-charge
and flag registers are located in address locations 08h
to 09h. During a multibyte access of the timekeeping
registers, when the address pointer reaches 07h—the
end of the clock and control register space—it wraps
around to location 00h. Writing the address pointer to
the corresponding location accesses address locations
08h and 09h. After accessing location 09h, the address
pointer wraps around to location 00h. On a I2C START,
STOP, or address pointer incrementing to location 00h,
the current time is transferred to a second set of registers. The time information is read from these secondary
registers, while the clock may continue to run. This
eliminates the need to reread the registers in case the
main registers update during a read.
Clock and Calendar
The time and calendar information is obtained by reading the appropriate register bytes. Table 3 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 day-of-week
Table 3. Address Map
ADDRESS
BIT 7
00H
EOSC
BIT 6
01H
X
02H
CEB
CB
03H
X
X
04H
X
X
05H
X
X
06H
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
FUNCTION
RANGE
Seconds
00–59
10 Seconds
Seconds
10 Minutes
Minutes
Minutes
00–59
Hours
Century/Hours
0–1; 00–23
Day
01–07
01–31
10 Hours
X
X
X
Day
10 Date
X
10 Month
10 Year
Date
Date
Month
Month
01–12
Year
Year
00–99
07H
OUT
FT
S
CAL4
CAL3
CAL2
CAL1
CAL0
Control
—
08H
TCS3
TCS2
TCS1
TCS0
DS1
DS0
ROUT1
ROUT0
Trickle Charger
—
09H
OSF
0
0
0
0
0
0
0
Flag
—
X = Read/Write bit
Note: Unless otherwise specified, the state of the registers is not defined when power is first applied.
8
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
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. Bit 7 of register 0 is the
enable oscillator (EOSC) bit. When this bit is set to 1,
the oscillator is disabled. When cleared to 0, the oscillator is enabled. The initial power-up value of EOSC is
0. The clock can be halted whenever the timekeeping
functions are not required, minimizing VBAT current
(IBACKUPDR) when VCC is not applied.
Location 02h is the century/hours register. Bit 7 and bit
6 of the century/hours register are the century-enable
bit (CEB) and the century bit (CB). Setting CEB to logic
1 causes the CB bit to toggle, either from a logic 0 to a
logic 1, or from a logic 1 to a logic 0, when the years
register rolls over from 99 to 00. If CEB is set to logic 0,
CB does not toggle.
On a power-on reset (POR), the time and date are set
to 00:00:00 01/01/00 (hh:mm:ss DD/MM/YY) and the
day register is set to 01.
When reading or writing the time and date registers,
secondary (user) buffers are used to prevent errors
when the internal registers update. When reading the
time and date registers, the user buffers are synchronized to the internal registers on any START or STOP
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 internal registers update during a read.
Bit 5: Calibration Sign Bit (S). A logic 1 in this bit indicates positive calibration for the RTC. A 0 indicates
negative calibration for the clock. See the Clock
Calibration section for a detailed description of the bit
operation. The initial power-up value of S is 0.
Bits 4 to 0: Calibration Bits (CAL4 to CAL0). These
bits can be set to any value between 0 and 31 in binary
form. See the Clock Calibration section for a detailed
description of the bit operation. The initial power-up
value of CAL0–CAL4 is 0.
The divider chain is reset whenever the seconds register is written. Write transfers occur on the acknowledge
from the DS1340. Once the divider chain is reset, to
avoid rollover issues, the remaining time and date registers must be written within one second.
The simplified schematic in Figure 6 shows the basic
components of the trickle charger. The trickle-charge
select (TCS) bits (bits 4–7) control the selection of the
trickle charger. To prevent accidental enabling, only a
BIT 7
TCS3
BIT 6
TCS2
BIT 5
TCS1
BIT 4
TCS0
1 OF 16 SELECT
NOTE: ONLY 1010b
ENABLES CHARGER
BIT 3
DS1
BIT 2
DS0
Special-Purpose Registers
The DS1340 has three additional registers (control,
trickle charger, and flag) that control the RTC, trickle
charger, and oscillator flag output.
Control Register (07h)
Bit 7: Output Control (OUT). This bit controls the output level of the FT/OUT pin when the FT bit is set to 0. If
FT = 0, the logic level on the FT/OUT pin is 1 if OUT = 1
and 0 if OUT = 0. The initial power-up OUT value is 1.
Bit 6: Frequency Test (FT). When this bit is 1, the
FT/OUT pin toggles at a 512Hz rate. When FT is written
to 0, the OUT bit controls the state of the FT/OUT pin.
The initial power-up value of FT is 0.
Trickle-Charger Register (08h)
BIT 1
BIT 0
ROUT1 ROUT0
TCS0-3 = TRICKLE-CHARGER SELECT
DS0-1 = DIODE SELECT
TOUT0-1 = RESISTOR SELECT
1 OF 2
SELECT
1 OF 3
SELECT
R1
250Ω
VCC
R2
2kΩ
VBACKUP
R3
4kΩ
Figure 6. Trickle Charger Functional Diagram
Maxim Integrated
9
DS1340
I2C RTC with Trickle Charger
Table 4. Trickle-Charge Register
TCS3
TCS2
TCS1
TCS0
DS1
DS0
ROUT1
ROUT0
X
X
X
X
0
0
X
X
Disabled
X
X
X
X
1
1
X
X
Disabled
X
X
X
X
X
X
0
0
Disabled
1
0
1
0
0
1
0
1
No diode, 250Ω resistor
1
0
1
0
1
0
0
1
One diode, 250Ω resistor
1
0
1
0
0
1
1
0
No diode, 2kΩ resistor
1
0
1
0
1
0
1
0
One diode, 2kΩ resistor
1
0
1
0
0
1
1
1
No diode, 4kΩ resistor
1
0
1
0
1
0
1
1
One diode, 4kΩ resistor
0
0
0
0
0
0
0
0
Power-on reset value
pattern on 1010 enables the trickle charger. All other
patterns disable the trickle charger. The trickle charger
is disabled when power is first applied. The diodeselect (DS) bits (bits 2, 3) select whether or not a diode
is connected between VCC and VBACKUP. If DS is 01,
no diode is selected; if DS is 10, a diode is selected.
The ROUT bits (bits 0, 1) select the value of the resistor
connected between VCC and VBACKUP. Table 3 shows
the resistor selected by the resistor select (ROUT) bits
and the diode selected by the diode select (DS) bits.
Warning: The ROUT value of 250Ω must not be selected whenever VCC is greater than 3.63V.
The user determines diode and resistor selection
according to the maximum current desired for battery
or super cap charging (Table 4). The maximum charging current can be calculated as illustrated in the following example.
Assume that a 3.3V system power supply is applied to
VCC and a super cap is connected to VBACKUP. Also
assume that the trickle charger has been enabled with
a diode and resistor R2 between VCC and VBACKUP.
The maximum current IMAX would therefore be calculated as follows:
IMAX = (3.3V - diode drop) / R2 ≈ (3.3V - 0.7V) /
2kΩ ≈ 1.3mA
As the super cap charges, the voltage drop between
VCC and VBACKUP decreases and therefore the charge
current decreases.
Flag Register (09h)
Bit 7: Oscillator Stop Flag (OSF). A logic 1 in this bit
indicates that the oscillator has stopped or was
stopped for some time period and may be used to
judge the validity of the clock and calendar data. This
bit is edge triggered and is set to logic 1 when the
10
FUNCTION
internal circuitry senses that the oscillator has transitioned from a normal run state to a STOP condition. 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 VCC and VBACKUP
are insufficient to support oscillation.
3) The EOSC bit is set to 1, disabling the
oscillator.
4)
External influences on the crystal (e.g., noise,
leakage).
The OSF bit remains at logic 1 until written to logic 0. It
can only be written to logic 0. Attempting to write OSF
to logic 1 leaves the value unchanged.
Bits 6 to 0: All other bits in the flag register read as 0
and cannot be written.
Clock Calibration
The DS1340 provides a digital clock calibration feature
to allow compensation for crystal and temperature variations. The calibration circuit adds or subtracts counts
from the oscillator divider chain at the divide-by-256
stage. The number of pulses blanked (subtracted for
negative calibration) or inserted (added for positive calibration) depends upon the value loaded into the five
calibration bits (CAL4–CAL0) located in the control register. Adding counts speeds the clock up and subtracting counts slows the clock down.
The calibration bits can be set to any value between 0
and 31 in binary form. Bit 5 of the control register, S, is
the sign bit. A value of 1 for the S bit indicates positive
calibration, while a value of 0 represents negative calibration. Calibration occurs within a 64-minute cycle.
The first 62 minutes in the cycle can, once per minute,
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
have a one-second interval where the calibration is performed. Negative calibration blanks 128 cycles of the
32,768Hz oscillator, slowing the clock down. Positive
calibration inserts 256 cycles of the 32,768Hz oscillator,
speeding the clock up. If a binary 1 is loaded into the
calibration bits, only the first two minutes in the 64minute cycle are modified. If a binary 6 is loaded, the
first 12 minutes are affected, and so on. Therefore,
each calibration step either adds 512 or subtracts 256
oscillator cycles for every 125,829,120 actual 32,678Hz
oscillator cycles (64 minutes). This equates to
+4.068ppm or -2.034ppm of adjustment per calibration
step. If the oscillator runs at exactly 32,768Hz, each of
the 31 increments of the calibration bits would represent +10.7 or -5.35 seconds per month, corresponding
to +5.5 or -2.75 minutes per month.
For example, if using the FT function, a reading of
512.01024Hz would indicate a +20ppm oscillator frequency error, requiring a -10(00 1010) value to be
loaded in the S bit and the five calibration bits.
slave on the I2C bus. Connections to the bus are made
through the open-drain I/O lines SDA and SCL. Within
the bus specifications a standard mode (100kHz max
clock rate) and a fast mode (400kHz max clock rate)
are defined. The DS1340 works in both modes.
The following bus protocol has been defined (Figure 7):
• Data transfer can be initiated only when the bus is
not busy.
• During data transfer, the data line must remain
stable whenever the clock line is high. Changes in
the data line while the clock line is high are interpreted as control signals.
Accordingly, the following bus conditions have been
defined:
Bus not busy: Both data and clock lines remain
high.
START data transfer: A change in the data line’s
state from high to low, while the clock line is high,
defines a START condition.
STOP data transfer: A change in the data line’s
state from low to high, while the clock line is high,
defines a STOP condition.
Data valid: The data line’s state represents valid
data when, after a START condition, the data line is
stable for the duration of the high period of the
clock signal. The data on the line must be changed
during the low period of the clock signal. There is
one clock pulse per bit of data.
Note: Setting the calibration bits does not affect the frequency test output frequency. Also note that writing to
the control register resets the divider chain.
I2C Serial Data Bus
The DS1340 supports a bidirectional I2C bus and data
transmission protocol. A device that sends data onto
the bus is defined as a transmitter and a device receiving data as a receiver. The device that controls the
message is called a master. The devices that are controlled by the master are slaves. A master device that
generates the serial clock (SCL), controls the bus
access, and generates the START and STOP conditions must control the bus. The DS1340 operates as a
MSB FIRST
MSB
Each data transfer is initiated with a START condition and terminated with a STOP condition. The
number of data bytes transferred between the
START and STOP conditions is not limited, and is
LSB
MSB
LSB
SDA
SLAVE
ADDRESS
SCL
1–7
IDLE
START
CONDITION
R/W
8
ACK
9
DATA
1–7
ACK
8
REPEATED IF MORE BYTES
ARE TRANSFERRED
9
DATA
1–7
ACK/
NACK
8
9
STOP CONDITION
REPEATED START
Figure 7. I2C Data Transfer Overview
Maxim Integrated
11
DS1340
I2C RTC with Trickle Charger
determined by the master device. The information
is transferred byte-wise and each receiver
acknowledges with a ninth bit.
Acknowledge: Each receiving device, when
addressed, is obliged to generate an acknowledge after the reception of each byte. The master
device must generate an extra clock pulse that is
associated with this acknowledge bit.
A device that acknowledges must pull down the
SDA line during the acknowledge clock pulse in
such a way that the SDA line is stable low during
the high period of the acknowledge-related clock
pulse. Setup and hold times must be taken into
account. A master must signal an end of data to
the slave by not generating an acknowledge bit on
the last byte that has been clocked out of the
slave. In this case, the slave must leave the data
line high to enable the master to generate the
STOP condition.
Figures 8 and 9 detail how data transfer is accomplished on the I2C bus. Depending upon the state of
the R/W bit, two types of data transfer are possible:
Data transfer from a master transmitter to a
slave receiver. The first byte transmitted by the
master is the slave address. Next follows a number of data bytes. The slave returns an acknowledge bit after each received byte.
Data transfer from a slave transmitter to a master receiver. The master transmits the first byte (the
slave address). The slave then returns an acknowledge bit. Next follows a number of data bytes transmitted by the slave to the master. The master
returns an acknowledge bit after all received bytes
other than the last byte. At the end of the last
received byte, a not acknowledge is returned.
The master device generates all the serial clock
pulses and the START and STOP conditions. A
transfer is ended with a STOP condition or with a
repeated START condition. Since a repeated
START condition is also the beginning of the next
serial transfer, the bus is not released.
The DS1340 can operate in the following two modes:
Slave Receiver Mode (Write Mode): Serial data
and clock are received through SDA and SCL.
12
After each byte is received, an acknowledge bit is
transmitted. Start and STOP conditions are recognized as the beginning and end of a serial transfer. Hardware performs address recognition after
reception of the slave address and direction bit.
The slave address byte is the first byte received
after the master generates the START condition.
The slave address byte contains the 7-bit DS1340
address, which is 1101000, followed by the direction bit (R/W), which is 0 for a write. After receiving
and decoding the slave address byte, the DS1340
outputs an acknowledge on SDA. After the
DS1340 acknowledges the slave address + write
bit, the master transmits a word address to the
DS1340. This sets the register pointer on the
DS1340, with the DS1340 acknowledging the
transfer. The master can then transmit zero or
more bytes of data, with the DS1340 acknowledging each byte received. The register pointer increments after each data byte is transferred. The
master generates a STOP condition to terminate
the data write.
Slave Transmitter Mode (Read Mode): The first
byte is received and handled as in the slave
receiver mode. However, in this mode, the direction bit indicates that the transfer direction is
reversed. The DS1340 transmits serial data on
SDA while the serial clock is input on SCL. Start
and STOP conditions are recognized as the beginning and end of a serial transfer. Hardware performs address recognition after reception of the
slave address and direction bit. The slave address
byte is the first byte received after the master generates the START condition. The slave address
byte contains the 7-bit DS1340 address, which is
1101000, followed by the direction bit (R/W),
which is 1 for a read. After receiving and decoding
the slave address byte, the DS1340 outputs an
acknowledge on SDA. The DS1340 then begins to
transmit data starting with the register address
pointed to by the register pointer. If the register
pointer is not written to before the initiation of a
read mode, the first address that is read is the last
one stored in the register pointer. The DS1340
must receive a not acknowledge to end a read.
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
<SLAVE
ADDRESS> <R/W>
S
1101000
0
<WORD ADDRESS (n)>
A
<DATA (n)>
XXXXXXXX
A
XXXXXXXX
S - START
MASTER TO SLAVE
A - ACKNOWLEDGE (ACK)
P - STOP
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
<DATA (n + X)
<DATA (n + 1)>
A
XXXXXXXX
A
...
XXXXXXXX
A
P
A
P
SLAVE TO MASTER
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
Figure 8. Data Write—Slave Receiver Mode
<SLAVE
ADDRESS> <R/W>
S
1101000
1
<DATA (n)>
A
<DATA (n + 1)>
XXXXXXXX
A
XXXXXXXX
S - START
MASTER TO SLAVE
A - ACKNOWLEDGE (ACK)
P - STOP
A - NOT ACKNOWLEDGE (NACK)
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
<DATA (n + X)>
<DATA (n + 2)>
A
XXXXXXXX
A
...
XXXXXXXX
SLAVE TO MASTER
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.
Figure 9. Data Read—Slave Transmitter Mode
<SLAVE
ADDRESS> <R/W>
S
1101000
<DATA (n)>
XXXXXXXX
0
A
XXXXXXXX
<DATA (n + 1)>
A
<SLAVE
ADDRESS> <R/W>
<WORD ADDRESS (n)>
XXXXXXXX
A
Sr
1101000
1
<DATA (n + 2)>
A
S - START
MASTER TO SLAVE
Sr - REPEATED START
A - ACKNOWLEDGE (ACK)
P - STOP
A - NOT ACKNOWLEDGE (NACK)
R/W - READ/WRITE OR DIRECTION BIT ADDRESS
XXXXXXXX
A
<DATA (n + X)>
A
...
XXXXXXXX
A
P
SLAVE TO MASTER
DATA TRANSFERRED
(X + 1 BYTES + ACKNOWLEDGE)
NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK.
Figure 10. Data Write/Read (Write Pointer, Then Read)—Slave Receive and Transmit
Maxim Integrated
13
DS1340
I2C RTC with Trickle Charger
Handling, PC Board Layout,
and Assembly
The DS1340C package contains a quartz tuning-fork
crystal. Pick-and-place equipment may be used, but
precautions should be taken to ensure that excessive
shocks are avoided. Exposure to reflow is limited to 2
times maximum. Ultrasonic cleaning should be avoided
to prevent damage to the crystal.
Avoid running signal traces under the package, unless
a ground plane is placed between the package and the
signal line. All N.C. (no connect) pins must be connected to ground.
Moisture-sensitive packages are shipped from the factory dry-packed.Handling instructions listed on the package label must be followed to prevent damage during
reflow. Refer to the IPC/JEDEC J-STD-020 standard for
moisture-sensitive device (MSD) classifications.
Pin Configurations
TOP VIEW
X1 1
8
VCC
7
FT/OUT
X2
2
VBACKUP
3
6
SCL
GND
4
5
SDA
DS1340
SCL 1
16 SDA
FT/OUT 2
15 GND
VCC 3
SO, μSOP
14 VBACKUP
DS1340C
N.C. 4
13 N.C.
N.C. 5
12 N.C.
N.C. 6
11 N.C.
N.C. 7
10 N.C.
N.C. 8
9
N.C.
SO (300 mils)
Package Information
Chip Information
PROCESS: CMOS
SUBSTRATE CONNECTED TO GROUND
Thermal Information
Theta-JA: 170°C/W (0.150in SO)
Theta-JC: 40°C/W (0.150in SO)
Theta-JA: 221°C/W (µSOP)
Theta-JC: 39°C/W (µSOP)
Theta-JA: 89.6°C/W (0.300in SO)
Theta-JC: 24.8°C/W (0.300in SO)
14
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.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.
8 SO (150 mils)
S8+2
21-0041
90-0096
8 µSOP
U8+1
21-0036
90-0092
16 SO (300 mils)
W16#H2
21-0042
90-0107
Maxim Integrated
DS1340
I2C RTC with Trickle Charger
Revision History
REVISION
NUMBER
REVISION
DATE
0
6/03
1
2
3
4
5
Maxim Integrated
7/04
12/04
11/05
3/06
8/08
DESCRIPTION
PAGES
CHANGED
Initial release.
—
Changed “2-wire” to “I2C” throughout the data sheet.
All
Added UL recognition info bullet to the Features section and to the VBACKUP pin
description.
1, 6
Added the “I/O Capacitance (SCL, SDA)” parameter (CI/O) to the AC Electrical
Characteristics table.
2
Added “SDA, SCL” and “VCC = 0V” to the “Supply Voltage, Pullup (FT/OUT)” parameter
and changed the symbol from “V IH” to “VPU ” in the Recommended DC Operating
Conditions table; in the DC Electrical Characteristics table, changed the “Oscillator
Current” parameter to “VBACKUP Current.”
3
Added the integrated-crystal and lead-free packages to the Ordering Information table;
added the integrated-crystal packages to the Features, Pin Configurations, Pin
Description.
1, 6
In Table 1, added increased crystal ESR with increased supply minimum voltage
requirement.
6
Added the DS1340C Only section.
7
Updated Figure 5 to also show the “C Version” crystal.
7
Added the Handling, PC Board Layout, and Assembly section.
12
Added the integrated-crystal package Theta-JA and Theta-JC information to the
Thermal Information section.
13
Updated the Ordering Information table to correct lead-free/RoHS packages.
1
In the General Description section, indicated that the time and date function continues
while powered by VBACKUP.
1
Updated the Typical Operating Circuit by removing pin numbers and adding a bypass
capacitor.
1
In the Pin Description, updated the VBACKUP description to indicate that no diodes
should be placed between the battery and pin and added the UL link; changed the
VCC description.
6
Added the Power Control section and new Table 1.
6
In the Handling, PC Board Layout, and Assembly section, added solder reflow
information for the RoHS SO package.
13
Added Package Information table.
14
Removed leaded part numbers from the Ordering Information table.
1
Removed the tRPU parameter and RST waveform from Figure 2. Replaced tRST with tREC.
5
In the Typical Operating Characteristics section, updated/changed the “FT vs.
VBACKUP” graph to “OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE (FT x 64).”
5
In the Pin Description, added pullup voltage information to the SDA, SCL, and FT/OUT
descriptions.
6
Updated Figure 5.
8
In the Clock and Calendar section, added text explaining the use of EOSC to halt the
oscillator.
9
Replaced Figure 7 with an updated version; changed Figures 8 and 9 and added
Figure 10 with more comprehensive I2C figures.
13
15
DS1340
I2C RTC with Trickle Charger
Revision History (continued)
REVISION
NUMBER
6
REVISION
DATE
10/10
DESCRIPTION
PAGES
CHANGED
Updated the top mark information in the Ordering Information table.
1
Updated the soldering information in the Absolute Maximum Ratings section.
2
Updated the SDA and SCL pin descriptions in the Pin Description table.
6
Increased ESR from 45,60k (max) to 80k (max) in Table 2.
7
Updated the Package Information table.
14
7
8/11
Raised VCC(MAX) limits for the -18 and -3 versions from 1.89V and 3.3V to 5.5V to
provide wide voltage functional operation; reorganized the EC tables and notes
8
4/13
Clarified VBACKUP in Absolute Maximum Ratings and updated Clock Calibration
section
2, 3
2, 9
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
16
© 2013 Maxim Integrated Products, Inc.
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.