DS1682 Datasheet, PDF (6/14 Pages) Dallas Semiconductor – Total Elapsed Time Recorder with Alarm

DS1682
Total-Elapsed-Time Recorder
with Alarm
Operation
The block diagram in Figure 1 shows the relationship
between the major functional blocks, the serial interface,
and the EEPROM memory section of the DS1682. Upon
power-up, the DS1682 transfers the contents of the
EEPROM into the counters and memory registers where
the data can be read and written through the serial inter-
face. The content of the counters and memory registers
are written into the EEPROM memory when the EVENT
pin transitions from a logic-high to a logic-low.
The DS1682 uses a calibrated, temperature-compensat-
ed RC time base to increment an ETC while an event
is active. When the event becomes active, the contents
of the nonvolatile EEPROM are transferred to the ETC
and event counter and the oscillator starts. As the event
continues, the ETC is incremented in quarter-second
increments. When the event becomes inactive, the event
counter is incremented and the contents of the ETC and
event counter are written to the nonvolatile EEPROM.
The ALARM output can be used to indicate when the ETC
has matched the value in the alarm register.
The DS1682 can be configured to prevent clearing the
alarm and the elapsed time and event counters.The user
memory can be separately write protected.
User-modified data is not stored in EEPROM until an
event becomes inactive.
Figure 2 shows the DS1682 measuring total run time and
operating from a battery with the alarm tied to an LED and
a pushbutton switch to trigger the alarm output.
Figure 3 shows the DS1682 in a total time-of-use applica-
tion where power may be removed at the same time as
the end of the event. The V_CC slew rate at power-down is
fast with respect to t_EW. A capacitor maintains V_CC on the
DS1682 above 2.5V until the EEPROM write completes. A
Schottky diode blocks current from the capacitor to other
devices connected to V_CC.
VCC
EVENT
VCC
LED
DS1682
ALARM
SCL
GND
SDA
0.01µF
30µF typ
Figure 3. Total Time-of-Use Application with Fast V_CC Slew Rate
The V_CC holding capacitor value of 30μF is calculated
using the maximum EEPROM write current and EEPROM
write time. This assumes that the V_CC slew rate allows
time from EVENT trip point to V_CC at 2.5V on the DS1682
is at least t_EW.
Figure 4 shows the DS1682 in a total time-of-use applica-
tion with power that can be removed at the sametime as
the end of the event. In this application, the V_CC slew rate
at power-down is slow with respect to t_EW. The external
reset IC (DS1816) ends the event as V_CC begins to drop.
V_CC must remain above 2.5V until the end of t_EW.
LED
PUSHBUTTON
SWITCH
TRIGGER SWITCH
EVENT
VCC
DS1682
ALARM
SCL
0.01µF
GND
SDA
Figure 2. Total Run Time
VCC
DS1816
LED
ALARM
VCC
DS1682
EVENT
SCL
GND
SDA
0.01µF
RPU
VCC
RPU
RPU = tR/ CBUS
Figure 4. Total Time-of-Use Application with Slow V_CC Slew Rate
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