Rainbow Electronics DS1682 - Manual (Page 14)

DS1682
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Figure 8. TOTAL RUN TIME
Figure 8 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 9. TOTAL TIME-OF-USE APPLICATION WITH FAST V
CC
SLEW RATE
Figure 9 shows the DS1682 in a total time-of-use application 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
.
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.