d1340-33 Maxim Integrated Products, Inc., d1340-33 Datasheet - Page 7

• Manufacturer Part Number: d1340-33
• Description: Ds1340, Ds1340c I?c Rtc With Trickle Charger
• Manufacturer: Maxim Integrated Products, Inc.

The DS1340 uses an external 32.768kHz crystal. The
oscillator circuit does not require any external resistors
or capacitors to operate. Table 2 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.
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
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.
The DS1340C integrates a standard 32,768Hz crystal
into the package. Typical accuracy with nominal V
and +25°C is approximately +15ppm. Refer to
Application Note 58 for information about crystal accu-
racy vs. temperature.
Table 2. 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 V
Figure 3. Oscillator Circuit Showing Internal Bias Network
Nominal
Frequency
Series Resistance
Load Capacitance
PARAMETER
C
L
1
X1
CRYSTAL
SYMBOL MIN
RTC
ESR
C
f
O
L
CC
X2
and V
C
Oscillator Circuit
L
2
Clock Accuracy
BACKUP
32.768
COUNTDOWN
TYP
12.5
CHAIN
REGISTERS
DS1340C Only
_____________________________________________________________________
RTC
are at least 2.0V.
45,60**
MAX
I
2
UNITS
C RTC with Trickle Charger
kHz
kΩ
pF
CC
The DS1340 operates as a slave device on the serial
bus. Access is obtained by implementing a START
condition and providing a device identification code fol-
lowed 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 V
V
blocked from any access. If V
the device power is switched from V
when V
V
V
ters are maintained from the V
is returned to nominal levels. The functional diagram
(Figure 5) shows the main elements of the serial RTC.
Figure 4. Layout Example
Figure 5. Functional Diagram
BACKUP
CC
BACKUP
"C" VERSION ONLY
V
LOCAL GROUND PLANE (LAYER 2)
falls below V
BACKUP
SCL
SDA
V
CC
CC
X1
X2
, the device power is switched from V
when V
AND ADDRESS
SERIAL BUS
drops below V
OSCILLATOR
INTERFACE
REGISTER
CONTROL
POWER
CC
CRYSTAL
is greater than V
CC
PF
, the internal clock registers are
drops below V
32,768Hz
DS1340
CALIBRATION
DIVIDER AND
CONTROL
CIRCUIT
LOGIC
PF
PF
. If V
BACKUP
is less than V
512Hz
PF
X1
X2
GND
PF
BACKUP
1Hz
. However, when
Operation
source until V
CC
is greater than
USER BUFFER
MUX/BUFFER
CLOCK AND
CALENDAR
REGISTERS
(7 BYTES)
to V
. The regis-
BACKUP
BACKUP
FT/OUT
CC
CC
to
7
,