GSM/GPRS Module Series
M66 Hardware Design
M66_Hardware_Design Confidential / Released 31 / 80
Use VRTC as the RTC power source.
If the main power supply (VBAT) is removed after the module is turned off, a backup supply such as a
coin-cell battery (rechargeable or non-chargeable) or a super-cap can be used to supply the VRTC pin to
keep the real time clock active.
Use VBAT and VRTC as the RTC power source.
As only powering the VRTC pin to keep the RTC will lead an error about 5 minutes a day, it is
recommended to power VBAT and VRTC pin at the same time when RTC function is needed. The
recommended supply for RTC core circuits are shown as below.
Non-chargeable
Backup Battery
Module
RTC
Core
VBAT
Power Supply
LDO/DCDC
LDO
VRTC
1.5K
Figure 11: VRTC is Supplied by a Non-chargeable Battery
Rechargeable
Backup Battery
Module
RTC
Core
VBAT
Power Supply
LDO/DCDC
LDO
VRTC
1.5K
Figure 12: VRTC is Supplied by a Rechargeable Battery
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