SIM900 Hardware Design
3.7 RTC Backup
The RTC (Real Time Clock) power supply of module can be provided by an external capacitor or a battery
(rechargeable or non-chargeable) through the VRTC.
Note: If the RTC function is enabled, a battery or capacitor should be connected with the VRTC pin. If RTC
Backup is not needed, please don’t keep it floating, a 4.7uF capacitor is recommended to connect to this pin.
The following figures show various sample circuits for RTC backup.
RTC
Core
10K
SIM900
VRTC
Non-chargeable
Backup Battery
Figure 16: RTC supply from non-chargeable battery
RTC
Core
10K
SIM900
VRTC
Rechargeable
Backup Battery
Figure 17: RTC supply from rechargeable battery
RTC
Core
10K
SIM900
VRTC
Large-capacitance
Capacitor
Figure 18: RTC supply from capacitor
z Li-battery backup
Coin-type Rechargeable Capacitor such as XH414H-IV01E form Seiko can be used.
SIM900_HD_V1.05 06.23.2010
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