DS1678 Maxim, DS1678 Datasheet - Page 8

• Manufacturer Part Number: DS1678
• Description: The DS1678 real-time clock (RTC) event recorder records the time and date of a nonperiodic, asynchronous event each time the active-low INT pin is activated
• Manufacturer: Maxim

POWER CONTROL
The device is fully accessible and data can be written and read when V
when V
switched from V
maintained from the V
above V
Table 1. Power Control
OSCILLATOR CIRCUIT
The DS1678 uses an external 32.768kHz crystal. The oscillator circuit does not require any external
resistors or capacitors (C
and the oscillator block in the Block Diagram shows a functional schematic of the oscillator circuit. Using
a crystal with the specified characteristics, the startup time is usually less than one second.
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 additional specifications.
CLOCK ACCURACY
The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match
between the capacitive load of the oscillator circuit and the capacitive 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 1 shows a
typical PC board layout for crystal and oscillator isolation from noise. Refer to Application Note 58:
Crystal Considerations with Dallas Real-Time Clocks for detailed information.
Figure 1. Typical Crystal Layout
Nominal Frequency
Series Resistance
Load Capacitance
V
V
V
CC
CC
CC
PARAMETER SYMBOL
LOCAL GROUND PLANE (LAYER 2)
CONDITION
< V
< V
> V
CC
PF
SUPPLY
, read and write access is allowed.
PF
PF
PF
CRYSTAL
falls below V
, V
, V
, V
CC
CC
CC
CC
< V
> V
> V
to V
BAT
BAT
BAT
BAT
L
BAT
) to operate. Table 2 specifies several crystal parameters for the external crystal,
PF
ESR
, the internal registers are blocked from any access. The device power is
source until V
C
f
READ/WRITE
O
when V
L
GND
X1
X2
ACCESS
Yes
No
No
CC
MIN
drops below V
CC
is returned to nominal levels (Table 1). After V
32.768
TYP
12.5
POWERED
8 of 25
V
V
V
BY
BAT
CC
CC
BAT
MAX
45
. Operation, except for the I
UNITS
kHz
k
pF
CC
is greater than V
2
C interface, is
PF
. However,
CC
returns