M41T00AUD clock operation
M41T00AUD
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5.4 Switchover
thresholds
While the M41T00AUD includes a precision reference for the backup switchover threshold, it
is not a fixed value, but depends on the backup voltage, V
BACK
. The device will always
switchover at the lesser of the reference voltage (V
PFD
, approximately 2.8V) and V
BACK
.
This ensures that it stays on V
CC
as long as possible before switching to the backup supply.
As shown in
Figure 13
, whenever V
BACK
is greater than V
PFD
, switchover occurs when V
CC
drops below V
PFD
.
Conversely, when V
BACK
is less than V
PFD
, switchover occurs when V
CC
drops below
V
BACK
.
Table 14
provides the values of these voltages.
Figure 13. Switchover thresholds
STATE
On VCC
On VBACK
On VCC
Switchover voltage
VSO = VBACK (< VPFD)
VPFD = 2.8V
VCC (= 3.3V)
Condition 2: VBACK < 2.8V (VPFD)
STATE
On VCC
On VBACK
On VCC
Switchover voltage
VSO = VPFD (= 2.8V)
VBACK (> VPFD)
VCC (= 3.3V)
Condition 1: VBACK > 2.8V (VPFD)
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