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Smart LTE Module Series
SC66 Hardware Design
SC66_Hardware_Design 47 / 118
3.6. VRTC Interface
The RTC (Real Time Clock) can be powered by an external power source through VRTC when the
module is powered down and there is no power supply for the VBAT. The external power source can be
rechargeable battery (such as button cells) according to application demands. The following reference
circuit design when an external battery is utilized for powering RTC.
VRTC
0R
100nF
Figure 10: RTC Powered by Rechargeable Button Cell
1. 2.1V~3.25V input voltage range and 3.0V typical value for VRTC, when VBAT is disconnected.
2. When powered by VBAT, the RTC error is 100ppm. When powered by VRTC, the RTC error is about
200ppm.
3. If the rechargeable battery is used, the ESR of battery should be less than 2K, and it is recommended
to use the MS621FE FL11E of SEIKO.
NOTES