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DS1340_06 Datasheet, PDF (6/14 Pages) Maxim Integrated Products – I2C RTC with Trickle Charger
I2C RTC with Trickle Charger
Pin Description
PIN
8 16
NAME
FUNCTION
1—
2—
X1
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
X2
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. Diodes placed in series between the supply and the input pin may
3
14
VBACKUP
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
5 16
61
GND
SDA
SCL
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
7
2
FT/OUT
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.
83
Primary Power Supply. When voltage is applied within normal limits, the device is fully accessible and data
VCC 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.
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.
Table 1. Power Control
SUPPLY CONDITION
READ/WRITE
ACCESS
VCC < VPF,
VCC < VBACKUP
No
VCC < VPF,
VCC > VBACKUP
No
VCC > VPF,
VCC < VBACKUP
Yes
VCC > VPF,
Yes
VCC > VBACKUP
POWERED
BY
VBAT
VCC
VCC
VCC
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