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DS1340Z-18 Datasheet(PDF) 6 Page - Maxim Integrated Products |
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DS1340Z-18 Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 13 page 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 pro- vides 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 fail- ures and automatically switches to the backup supply. 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 crys- tal 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. 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 capaci- tive load for which the crystal was trimmed. Additional I2C RTC with Trickle Charger 6 _____________________________________________________________________ Pin Description PIN 8 16 NAME FUNCTION 1 — X1 2 — X2 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. 3 14 VBACKUP 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. 4 15 GND Ground 5 16 SDA Serial Data Input/Output. SDA is the data input/output for the I 2C 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 I 2C 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. 8 3 VCC DC Power for Primary Power Supply — 4–13 N.C. No Connection. Must be connected to ground. PARAMETER SYMBOL MIN TYP MAX UNITS Nominal Frequency fO 32.768 kHz Series Resistance ESR 45,60** kΩ Load Capacitance CL 12.5 pF Table 1. Crystal Specifications* *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 addi- tional specifications. **A crystal with up to 60kΩ ESR can be used if the minimum operating voltages on both VCC and VBACKUP are at least 2.0V. COUNTDOWN CHAIN RTC X1 X2 CL1 CL2 CRYSTAL RTC REGISTERS Figure 3. Oscillator Circuit Showing Internal Bias Network |
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