CPU 72x
24.05.2019
page 23
1.6.7
RAM and RTC Buffering
WARNING
Non-rechargeable lithium battery
Injury from explosion
Under no circumstances recharge the lithium battery
The lithium battery RBA 721 has a capacity of 3.0 V, 190 mAh. Assuming a typical current
consumption of 10 µA (at 25°C), this corresponds to a backup duration of 750 days. This
value applies if the CPU is never connected to the supply voltage.
If the CPU is operated from the power supply for 12 h per day, for example, this results in
a proportional increase in the backup time. In this case, the backup time is doubled to
4 years.
Fig.17: Battery backup time of the CPU 72x-Tx/CTx
IMPORTANT
The service life of the battery is restricted to 5 years even given optimum
backup.
The battery must be renewed after 5 years even in devices that are in store.
Typical current consumption at 25°C is 10
µA
However, current consumption may vary between 5
µA and 40
µA depending
on the temperature.
1.6.8
Startup Behavior
After switch on of the power supply the monitoring circuit activates the reset up to the
voltage is stabilized (max. 50
ms after surpassing the level of 4.65
Vdc). As soon as this
process is executed, the run time system starts in the Flash-EPROM.
Battery backup time
0
1
2
3
4
5
6
7
0%
20%
40%
60%
80%
100%
Pow er supplied tim e [%]
B
a
c
k
u
p
t
im
e
[
y
e
a
rs
]
Max.battery service life 5 years
