RA8804 CE
Page - 35
ETM60E-02
8.11. Backup and Recovery
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 VDD = 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 I2C, completion of less than 1 second is recommended.
If such communication requires 2 seconds (Max.) or longer, the I2C bus interface is reset by the internal
bus timeout function.
When bus-time-out occur, SDA turns to Hi-Z input mode.
But 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.
*
:
tR2
is specifications for an oscillation not to stop. Some clocks are not output by an FOUT terminal.
Item
Symbol
Condition
Min.
Typ.
Max.
Unit.
Power supply rise time1
tR1
VDD = VSS to 5.5 V
1
-
10
ms/V
Access wait time
(After initial power on)
tCL
After VDD = VDET
30
-
-
ms
Power supply fall time
tF
VDD = 5.5 V to VDET
100
-
-
µs/V
Power supply rise time2
tR2
VDD = VDET to 5.5 V
15
-
-
µs/V
Setup time from
Finish of I2C.
tCD
Before VDD = VDET
0
-
-
µs
VDET
tF
Back-up operation
VDD
Communication
Non-Communication
0V
Non-Communication
I2C-BUS Communication state
*
tR2
tR1
tCL
tCD