RX8804CE
Page - 37
ETM59E-05
8.10. Backup and Recovery
Figure 25 V
DD
Sequence
This circuit is sensitive to power supply noise and supply voltage should be stabilized to avoid negative impact on the
accuracy.
tR1 is needed for a proper power-on reset. If this power-on condition cannot be kept, it is necessary to send an
initialization routine to the RTC by software.
In case of repeated ON / OFF of the power supply within short term, it is possible that the power-on reset becomes
unstable.
After power-OFF, keep V
DD
= GND for more than 10 seconds for a proper power-on reset.
When it is impossible, please initialize the RTC by the software.
As for the communication of I
2
C-Bus, completion of less than 1 second is recommended.
If such communication requires 2 seconds (Max.) or longer, the I
2
C-Bus interface is reset by the internal bus timeout
function.
When bus-time-out occur, SDA turns to Hi-Z input mode. readout data of a clock is stable anytime, and there isn't
contradiction.
And it does not occur that data of a clock delay even if access time is prolonged.
Table 59 V
DD
sequence characteristics
Item
symbol
Condition
Min.
Typ.
Max.
Unit
Power supply rise time1
tR1
V
DD
= V
SS
~ 5.5 V
1
10
ms / V
Access wait time
(after initial power on)
tCL
After V
DD
= V
DET
30
ms
Power supply fall time
tF
V
DD
= 5.5 V ~ V
DET
100
µ
s / V
Power supply rise time
tR2
V
DD
= V
DET
~ 5.5 V
15
µ
s / V
Setup time from finish of I
2
C-Bus
tCD
Before V
DD
= V
DET
0
µ
s
V
DET
tF
Back-up operation
V
DD
Communication
Non-Communication
0V
Non-Communication
I
2
C-Bus Communication state
*
tR2
tR1
tCL
tCD
*
:
tR2
is specifications for an oscillation not to stop. Some clocks are not output by an FOUT terminal.