DS1337_09 Datasheet, PDF (6/16 Pages) Maxim Integrated Products – I2C Serial Real-Time Clock

DS1337 I²C Serial Real-Time Clock
BLOCK DIAGRAM
X1
C_L
1Hz/4.096kHz/8.192kHz/32.768kHz
1Hz
MUX/
BUFFER
N
SQW/INTB
X2
C_L
"C" version only
CONTROL
LOGIC
ALARM,
TRICKLE
CHARGE, AND
CONTROL
REGISTERS
INTA
N
SCL
SDA
SERIAL BUS
INTERFACE AND
ADDRESS
REGISTER
DS1337
CLOCK AND
CALENDAR
REGISTERS
USER BUFFER
(7 BYTES)
DETAILED DESCRIPTION
The Block Diagram shows the main elements of the DS1337. As shown, communications to and from the DS1337
occur serially over an I²C bus. The DS1337 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 through
the I²C interface whenever V_CC is between 5.5V and 1.8V. I²C operation is not guaranteed when V_CC is below 1.8V.
The DS1337 maintains the time and date when V_CC is as low as 1.3V.
OSCILLATOR CIRCUIT
The DS1337 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. The Block Diagram
shows a functional schematic of the oscillator circuit. The startup time is usually less than 1 second when using a
crystal with the specified characteristics.
Table 1. Crystal Specifications*
PARAMETER
Nominal Frequency
Series Resistance
Load Capacitance
SYMBOL
f_O
ESR
C_L
MIN TYP MAX
32.768
50
6
UNITS
kHz
k
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.
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