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DS1340C-3- Datasheet(PDF) 6 Page - Maxim Integrated Products |
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DS1340C-3- Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 14 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. Power Control The power-control function is provided by a precise, temperature-compensated voltage reference and a comparator circuit that monitors the VCC 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 from any access. If VPF is less than VBACKUP, 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 when VCC drops below VBACKUP. The registers are maintained from the VBACKUP source until VCC is returned to nominal levels (Table 1). After VCC returns above VPF, read and write access is allowed tREC. 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. 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. 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.maxim-ic.com/qa/info/ul). 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 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 VTP, 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. SUPPLY CONDITION READ/WRITE ACCESS POWERED BY VCC < VPF, VCC < VBACKUP No VBAT VCC < VPF, VCC > VBACKUP No VCC VCC > VPF, VCC < VBACKUP Yes VCC VCC > VPF, VCC > VBACKUP Yes VCC Table 1. Power Control |
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