Datasheet

DocID12615 Rev 8 15/56
M41T93 Operation
56
2.3 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 (see Figure 22 on page 47). 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.
2.4 Power-on reset (t
rec
)
The M41T93 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.