RTC – 4553AC
Page - 16
MQ - 342 - 01
8.3.9. Power-On Reset
When the system power is turned on, the power-on reset function operates automatically, performing a
sequence identical to system reset. However, because the PONC bit remains at "1", a system reset must be
performed to set the PONC bit to "0" before setting the time and calendar.
The conditions for power-on reset and the conditions for data retention and normal IC operation during power
fluctuation are shown below.
t1: Condition for power-on reset
t2: Condition for data retention and normal
IC operation during power-on
Note: 3 V and 5 V are recommended
voltages. 2 V is the backup voltage.
V
DD
t
1
5
[ V ]
4
3
2
1
0
t
2
t
Ta =
−
30 °C to +70 °C
t 1
Condition tR for power-on reset
at 0
+0.3
V
→
3 V or 0
+0.3
V
→
5 V
(Note 1)
1.0
µ
s/V
≤
t
R
≤
1.6 ms/V
t 2
Condition tR for no power-on reset
at 2 V
→
3 V or 2 V
→
5 V
(Note 2)
1.0
µ
s/V
≤
t
R
≤
1.6 ms/V
Note 1 The voltage level before initial power-on should be 0.3 V or less. If powering up from an intermediate
potential, power-on reset may not be performed correctly. Be sure to verify correct operation.
Note 2 Within the voltage range for data retention and clock operation (2.0 V - 5.5 V), power-on reset is designed
not to be performed under the above conditions, to prevent data loss. When the voltage level falls below 2
V, operation and data retention are no longer assured.
Note 3 During power-on or power restoration from an intermediate potential outside of the assured operation
range (0.3 V - 1.9 V), the power-on reset circuit will not operate normally, leading to possible malfunction. If
the backup battery voltage has fallen below 2.0 V, the V
DD
pin of the RTC must be temporarily set to
ground potential before restoring the power.
8.3.10. Power Supply Connection Example
Use a high capacitance value here to guard
against reverse current flowing from the collector
to the emitter of the transistor during transition
from power on to power off.
Power-down
detection circuit
0.1
µ
F
GND
CS
1
V
DD
RTC
+
R
+
+5 V
+5 V +V
CE
Secondary battery or lithium battery. (Lithium battery
requires the diode shown in . Regarding the value of
the resistor R, consult the battery manufacturer.
electronic components distributor
