SimCom SIM8905A User Manual page 11

Power off
Users can power off SIM8905A by pulling down the PWRKEY pin for more than 8 seconds.
VRTC
VRTC is the power supply for RTC circuit and charger output for coin cell or backup battery. If RTC support is
needed when the battery is removed, a qualified coin cell or keep-alive capacitor is required on the VRTC pin.
When VBAT is present and valid, coin cell charging is enabled through software control and powered from VBAT.
Reference circuits are shown as below:
Keep-alive capacitor:
Non-rechargeable battery:
Rechargeable battery:
VRTC typical voltage is 3.0V, and the current consumption is about 5uA when VBAT is absence. For electrical
characteristics, please refer to Table 23: VRTC characteristic.
Figure9: Timing of power on module
VRTC
Capacitor
Figure 10: Keep-alive capacitor
Non-rechargeable
battery
Figure 11: Non-rechargeable battery
VRTC
Rechargeable
battery
Figure 12: Rechargeable battery
Smart Machine Smart Decision
Module
RTC
Module
VRTC
RTC
Module
RTC
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