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Rev 2; 12/04
I2C RTC with Trickle Charger
General Description
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. The device is programmed serially through an I2CTM bidirectional bus.
Features
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 SOP or SO Packages Underwriters Laboratory (UL) Recognized
DS1340
Applications
Portable Instruments Point-of-Sale Equipment Medical Equipment Telecommunications
Ordering Information
PART DS1340Z-18 DS1340Z-3 DS1340Z-33 TEMP RANGE PIN-PACKAGE TOP MARK D1340-18 DS1340-3 D1340-33 1340 A1-18 1340 A1-3 1340 A1-33 1340C-18 1340C-3 1340C-33 D1340-18 DS1340-3 D1340-33 1340 A1-18 1340 A1-3 1340 A1-33 1340C-18 1340C-3 1340C-33
-40C to +85C 8 SO (0.150in) -40C to +85C 8 SO (0.150in) -40C to +85C 8 SO (0.150in) -40C to +85C 8 SOP -40C to +85C 8 SOP -40C to +85C 8 SOP -40C to +85C 16 SO -40C to +85C 16 SO -40C to +85C 16 SO -40C to +85C 8 SO (0.150in) -40C to +85C 8 SO (0.150in) -40C to +85C 8 SO (0.150in) -40C to +85C 8 SOP -40C to +85C 8 SOP -40C to +85C 8 SOP -40C to +85C 16 SO -40C to +85C 16 SO -40C to +85C 16 SO
Typical Operating Circuit
VCC CRYSTAL VCC RPU RPU 1 X1 6 SCL CPU 5 SDA RPU = tR / CB 2 X2 8 VCC 7 FT/OUT
DS1340U-18 DS1340U-3
VCC
DS1340U-33 DS1340C-18 DS1340C-3 DS1340C-33 DS1340Z-18+ DS1340Z-3+ DS1340Z-33+ DS1340U-18+ DS1340U-3+ DS1340U-33+
DS1340
VBACKUP GND 4
3
I2C is a trademark of Philips Corp. Purchase of I2C components from Maxim Integrated Products, Inc., or one of its sublicensed Associated Companies, conveys a license under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips.
DS1340C-18+ DS1340C-3+ DS1340C-33+
Note: A "+" in the part number and a "+" anywhere on the top mark indicates a lead-free device. Pin Configurations appear at end of data sheet.
______________________________________________ Maxim Integrated Products
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For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
I2C RTC with Trickle Charger DS1340
ABSOLUTE MAXIMUM RATINGS
Voltage Range on VCC Pin 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) Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-55C to +125C Soldering Temperature Range............................See IPC/JEDEC J-STD-020 Specification
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.
AC ELECTRICAL CHARACTERISTICS
(VCC = VCC MIN to VCC MAX, TA = -40C to +85C, unless otherwise noted.) (Note 1, Figure 1)
PARAMETER SCL Clock Frequency Bus Free Time Between STOP and START Conditions Hold Time (Repeated) START Condition (Note 2) Low Period of SCL Clock High Period of SCL Clock Data Hold Time (Notes 3, 4) Data Setup Time (Note 5) START Setup Time Rise Time of SDA and SCL Signals (Note 6) Fall Time of SDA and SCL Signals (Note 6) Setup Time for STOP Condition Capacitive Load for Each Bus Line I/O Capacitance (SCL, SDA) Pulse Width of Spikes that Must be Suppressed by the Input Filter Oscillator Stop Flag (OSF) Delay SYMBOL fSCL tBUF tHD:STA tLOW tHIGH tHD:DAT tSU:DAT tSU:STA tR tF tSU:STO CB CI/O tSP tOSF Fast mode (Note 7) CONDITIONS Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode Standard mode Fast mode (Note 6) 10 30 100 MIN 0 100 4.7 1.3 4.0 0.6 4.7 1.3 4.0 0.6 0 0 250 100 4.7 0.6 20 + 0.1CB 20 + 0.1CB 20 + 0.1CB 20 + 0.1CB 4.7 0.6 400 1000 300 300 300 0.9 0.9 TYP MAX 100 400 UNITS kHz s s s s s ns s ns ns s pF pF ns ms
2
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I2C RTC with Trickle Charger
RECOMMENDED DC OPERATING CONDITIONS
(VCC = VCC MIN to VCC MAX, TA = -40C to +85C, unless otherwise noted. Typical values are at VCC = 3.3V, TA = +25C, unless otherwise noted.) (Note 1)
PARAMETER Supply Voltage (Note 8) Input Logic 1 (SDA, SCL) Input Logic 0 (SDA, SCL) Supply Voltage, Pullup (FT/OUT, SDA, SCL), VCC = 0V Backup Supply Voltage (Note 8) SYMBOL DS1340-18 VCC VIH VIL VPU DS1340-3 DS1340-33 (Note 8) (Note 8) (Note 8) DS1340-18 VBACKUP R1 Trickle-Charge Current-Limiting Resistors R2 R3 Power-Fail Voltage (Note 8) Input Leakage (SCL, CLK) I/O Leakage (SDA, FT/OUT) SDA Logic 0 Output VPF ILI ILO IOLSDA VCC > 2V; VOL = 0.4V 1.7V < VCC < 2V; VOL = 0.2 x VCC VCC > 2V; VOL = 0.4V FT/OUT Logic 0 Output IOLSQW 1.7V < VCC < 2V; VOL = 0.2 x VCC 1.3V < VCC < 1.7V; VOL = 0.2x VCC DS1340-18 Active Supply Current (Note 13) ICCA DS1340-3 DS1340-33 DS1340-18 Standby Current (Note 14) VBACKUP Leakage Current ICCS DS1340-3 DS1340-33 IBACKUPLKG VBACKUP = 3.7V 72 108 192 60 81 100 DS1340-3 DS1340-33 (Notes 9, 10) (Note 11) (Note 12) DS1340-18 DS1340-3 DS1340-33 1.51 2.45 2.70 -1 -1 1.3 1.3 1.3 250 2000 4000 1.6 2.6 2.88 1.71 2.7 2.97 +1 +1 3.0 3.0 3.0 3.0 250 150 200 300 100 125 150 100 nA A A A A mA mA A V CONDITIONS MIN 1.71 2.7 2.97 0.7 x VCC -0.3 TYP 1.8 3.0 3.3 MAX 1.89 3.3 5.5 VCC + 0.3 +0.3 x VCC 5.5 3.7 3.7 5.5 V V V V UNITS V
DS1340
DC ELECTRICAL CHARACTERISTICS
(VCC = 0V, VBACKUP = 3.7V, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER SYMBOL IBACKUP1 IBACKUP2 IBACKUP3 VBACKUP Data-Retention Current CONDITIONS OSC ON, FT = 0 (Note 15) OSC ON, FT = 1 (Note 15) OSC ON, FT = 0, VBACKUP = 3.0V, TA = +25C (Notes 15, 16) MIN TYP 800 850 800 25.0 MAX 1150 1250 1000 100 nA UNITS
VBACKUP Current
nA
IBACKUPDR OSC OFF
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I2C RTC with Trickle Charger DS1340
POWER-UP/POWER-DOWN CHARACTERISTICS
(TA = -40C to +85C) (Figure 2)
PARAMETER Recovery at Power-Up VCC Fall Time; VPF(MAX) to VPF(MIN) VCC Rise Time; VPF(MIN) to VPF(MAX) SYMBOL tREC tVCCF tVCCR (Note 17) 300 0 CONDITIONS MIN TYP MAX 2 UNITS ms s s
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: Limits at -40C 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. All voltages are referenced to ground. Measured at VCC = typ, VBACKUP = 0V, register 08h = A5h. The use of the 250 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 +25C are guaranteed by design and not production tested. This delay applies only if the oscillator is enabled and running. If the oscillator is disabled or stopped, no power-up delay occurs.
Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: Note 16: Note 17:
SDA
tBUF tLOW tR tF
tHD:STA
tSP
SCL tHD:STA STOP START tHD:DAT tHIGH tSU:DAT REPEATED START tSU:STA tSU:STO
Figure 1. Data Transfer on I2C Serial Bus 4 _____________________________________________________________________
I2C RTC with Trickle Charger DS1340
VCC VPF(MAX) VPF(MIN) tF
VPF
VPF
tR tRPU tRST
RST
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 = +25C, unless otherwise noted.)
ICCSA vs. VCC FT = 0
DS1340 toc01
ICCS vs. VCC FT = 0
DS1340 toc02
IBACKUP1 (FT = 0) vs. VBACKUP
800 SUPPLY CURRENT (nA) 750 700 650 600 550 500
DS1340 toc03
250
150 125 SUPPLY CURRENT (A) 100 -3.0V 75 50 25 -1.8V
850
200 SUPPLY CURRENT (A)
-3.3V
150
100
50
450 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VCC (V) 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VCC (V) 400 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VBACKUP (V)
IBACKUP2 (FT = 1) vs. VBACKUP
DS1340 toc04
IBACKUP3 vs. TEMPERATURE
850 800 SUPPLY CURRENT (nA) 750 700 650 600 550 500 FREQUENCY (Hz) VBACKUP = 3.0V
DS1340 toc05
FT vs. VBACKUP
511.9995 511.9990 511.9985 511.9980 511.9975 511.9970 511.9965 511.9960 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VBACKUP (V)
DS1340 toc06
850 800 SUPPLY CURRENT (nA) 750 700 650 600 550 500 450 400
512.0000
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VBACKUP (V)
-40
-20
0
20
40
60
80
TEMPERATURE (C)
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I2C RTC with Trickle Charger DS1340
Pin Description
PIN 8 1 2 16 -- -- NAME X1 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 floated 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. VBACKUP can be as high as 5.5V on the 3.3V device. 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. Ground 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. Serial Clock Input. SCL is the clock input for the I2C interface and is used to synchronize data movement on the serial interface. 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. DC Power for Primary Power Supply No Connection. Must be connected to ground.
3
14
VBACKUP
4 5 6
15 16 1
GND SDA SCL
7
2
FT/OUT
8 --
3 4-13
VCC N.C.
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.
Table 1. Crystal Specifications*
PARAMETER Nominal Frequency Series Resistance Load Capacitance SYMBOL fO ESR CL MIN TYP 32.768 45,60** 12.5 MAX UNITS kHz k pF
Oscillator Circuit
The DS1340 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 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 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. **A crystal with up to 60k ESR can be used if the minimum operating voltages on both VCC and VBACKUP are at least 2.0V.
RTC
COUNTDOWN CHAIN
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
6
CL1
CL2
RTC REGISTERS
X1 CRYSTAL
X2
Figure 3. Oscillator Circuit Showing Internal Bias Network _____________________________________________________________________
I2C RTC with Trickle Charger DS1340
LOCAL GROUND PLANE (LAYER 2)
X1 X2 OSCILLATOR
32,768Hz DIVIDER AND CALIBRATION CIRCUIT
512Hz MUX/BUFFER
FT/OUT
X1 CRYSTAL X2
"C" VERSION ONLY VCC VBACKUP POWER CONTROL
SCL SDA
CONTROL LOGIC SERIAL BUS INTERFACE AND ADDRESS REGISTER
1Hz CLOCK AND CALENDAR REGISTERS
USER BUFFER (7 BYTES)
GND
DS1340
Figure 4. Layout Example
Figure 5. Functional Diagram
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 the crystal and oscillator from noise. Refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks (www.maxim-ic.com/RTCapps) for detailed information.
DS1340C Only
The DS1340C integrates a standard 32,768Hz crystal into the package. Typical accuracy with nominal VCC and +25C is approximately +15ppm. Refer to Application Note 58 for information about crystal accuracy vs. temperature.
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.
Operation
The DS1340 operates as a slave device on the serial bus. Access is obtained by implementing a START
Address Map
Table 2 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
Table 2. Address Map
ADDRESS 00H 01H 02H 03H 04H 05H 06H 07H 08H 09H OUT TCS3 OSF FT TCS2 0 BIT 7 EOSC X CEB X X X CB X X X X 10 Year S TCS1 0 CAL4 TCS0 0 CAL3 DS1 0 CAL2 DS0 0 X 10 Date 10 Month BIT 6 BIT 5 10 Seconds 10 Minutes 10 Hours X X Date Month Year CAL1 ROUT1 0 CAL0 ROUT0 0 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION Seconds Minutes Century/Hours Day Date Month Year Control Trickle Charger Flag RANGE 00-59 00-59 0-1; 00-23 01-07 01-31 01-12 00-99 -- -- -- Seconds Minutes Hours Day
X = Read/Write bit Note: Unless otherwise specified, the state of the registers is not defined when power is first applied. _____________________________________________________________________ 7
I2C RTC with Trickle Charger DS1340
BIT 7 TCS3
BIT 6 TCS2
BIT 5 TCS1
BIT 4 TCS0
BIT 3 DS1
BIT 2 DS0
BIT 1 BIT 0 ROUT1 ROUT0 TCS0-3 = TRICKLE-CHARGER SELECT DS0-1 = DIODE SELECT TOUT0-1 = RESISTOR SELECT
1 OF 16 SELECT NOTE: ONLY 1010b ENABLES CHARGER
1 OF 2 SELECT
1 OF 3 SELECT
R1 250 R2 2k R3 4k
VCC
VBACKUP
Figure 6. Trickle Charger Functional Diagram
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 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 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. 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. Location 02h is the century/hours register. Bit 7 and bit 6 of the century/hours register are the century-enable
8
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. 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. 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.
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.
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I2C RTC with Trickle Charger
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. 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. ing 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) / 2k 1.3mA As the super cap charges, the voltage drop between VCC and VBACKUP decreases and therefore the charge current decreases.
DS1340
Trickle-Charger Register (08h)
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 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 250 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 3). The maximum charg-
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 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) 2) 3) 4) The first time power is applied. The voltages present on VCC and VBACKUP are insufficient to support oscillation. The EOSC bit is set to 1, disabling the oscillator. 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.
Table 3. Trickle-Charge Register
TCS3 X X X 1 1 1 1 1 1 0 TCS2 X X X 0 0 0 0 0 0 0 TCS1 X X X 1 1 1 1 1 1 0 TCS0 X X X 0 0 0 0 0 0 0 DS1 0 1 X 0 1 0 1 0 1 0 DS0 0 1 X 1 0 1 0 1 0 0 ROUT1 X X 0 0 0 1 1 1 1 0 ROUT0 X X 0 1 1 0 0 1 1 0 Disabled Disabled Disabled No diode, 250 resistor One diode, 250 resistor No diode, 2k resistor One diode, 2k resistor No diode, 4k resistor One diode, 4k resistor Power-on reset value FUNCTION
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I2C RTC with Trickle Charger DS1340
SDA
MSB SLAVE ADDRESS R/W DIRECTION BIT ACKNOWLEDGEMENT SIGNAL FROM RECEIVER SCL 1 START CONDITION 2 6 7 8 9 ACK REPEATED IF MORE BYTES ARE TRANSFERED 1 2 3-7 8 9 ACK STOP CONDITION OR REPEATED START CONDITION ACKNOWLEDGEMENT SIGNAL FROM RECEIVER
Figure 7. I2C Data Transfer Overview
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, 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 repre10
sent +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. 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 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.
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I2C RTC with Trickle Charger DS1340
ADDRESS> S 1101000 0 A XXXXXXXX A XXXXXXXX A XXXXXXXX A XXXXXXXX A P ADDRESS> S 1101000 1 A XXXXXXXX A XXXXXXXX A XXXXXXXX A XXXXXXXX A P DATA TRANSFERRED S -- START (X + 1 BYTES + ACKNOWLEDGE) A -- ACKNOWLEDGE NOTE: LAST DATA BYTE IS FOLLOWED BY P -- STOP A NOT ACKNOWLEDGE (A) SIGNAL A -- NOT ACKNOWLEDGE R/W -- READ/WRITE OR DIRECTION BIT ADDRESS = D0H
S -- START DATA TRANSFERRED A -- ACKNOWLEDGE (X + 1 BYTES + ACKNOWLEDGE) P -- STOP R/W -- READ/WRITE OR DIRECTION BIT ADDRESS = D0H

Figure 8. Slave Receiver Mode (Write Mode)
Figure 9. Slave Transmitter Mode (Read Mode
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. 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 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. 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
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I2C RTC with Trickle Charger
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.
DS1340
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. 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. The SO package may be reflowed as long as the peak temperature does not exceed 240C. Peak reflow temperature ( 230C) duration should not exceed 10 seconds, and the total time above 200C should not exceed 40 seconds (30 seconds nominal). Exposure to reflow is limited to 2 times maximum. 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
SCL 1 FT/OUT 2 X1 1 X2 VBACKUP GND 2 3 4 8 VCC FT/OUT SCL SDA VCC 3 N.C. 4 N.C. 5 N.C. 6 N.C. 7 N.C. 8 16 SDA 15 GND 14 VBACKUP
DS1340
7 6 5
DS1340C
13 N.C. 12 N.C. 11 N.C. 10 N.C. 9 N.C.
SO, SOP
SO (300 mils)
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I2C RTC with Trickle Charger
Chip Information
TRANSISTOR COUNT: 10,930 PROCESS: CMOS SUBSTRATE CONNECTED TO GROUND
Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.
DS1340
Thermal Information
Theta-JA: +170C/W (0.150in SO) Theta-JC: +40C/W (0.150in SO) Theta-JA: +221C/W (SOP) Theta-JC: +39C/W (SOP) Theta-JA: +89.6C/W (0.300in SO) Theta-JC: +24.8C/W (0.300in SO)
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
is a registered trademark of Dallas Semiconductor Corporation.

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