Datasheet

Operation M41T82, M41T83
18/64 DocID012578 Rev 16
2.4 Data retention and battery switchover (V
SO
= V
RST
)
Once V
CC
falls below the switchover voltage (V
SO
= V
RST
), the device automatically
switches over to the battery and powers down into an ultra low current mode of operation to
preserve battery life. If V
BAT
is less than, or greater than V
RST
, the device power is switched
from V
CC
to V
BAT
when V
CC
drops below V
RST
(see Figure 28 on page 54). At this time the
clock registers and user RAM will be maintained by the attached battery supply.
When it is powered back up, the device switches back from battery to V
CC
at V
SO
+
hysteresis. When V
CC
rises above V
RST
, it will recognize the inputs. For more information
on battery storage life refer to Application Note AN1012.
2.5 Power-on reset (t
rec
)
The M41T8x continuously monitors V
CC
. When V
CC
falls to the power fail detect trip point,
the RST output pulls low (open drain) and remains low after power-up for t
rec
(210 ms
typical) after V
CC
rises above V
RST
(max).
Note: The t
rec
period does not affect the RTC operation. Write protect only occurs when V
CC
is
below V
RST
. When V
CC
rises above V
RST
, the RTC will be selectable immediately. Only the
RST output is affected by the t
rec
period.
The RST pin is an open drain output and an appropriate pull-up resistor to V
CC
should be
chosen to control the rise time.