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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 a
rechargeable battery (such as a button cell battery) according to application demands. A reference circuit
design is shown .
Figure 11: RTC Powered by a Rechargeable Button Cell Battery
NOTES
1.
When VBAT is disconnected, the recommended input voltage range for VRTC is 2.1V~3.25V and the
recommended typical value is 3.0V.
2.
When powered by VBAT, the RTC error is 100ppm. When powered by VRTC, the RTC error is about
200ppm.
If a rechargeable battery is used, the ESR of battery should be less than 2KΩ, and it is recommended
3.
to use the MS621FE FL11E of SEIKO.
4.
If RTC function is not needed, then it is recommended to connect a 47uF capacitor to the VRTC
interface.
SC66_Hardware_Design
VRTC
0R
100nF
BAT
Smart LTE Module Series
SC66 Hardware Design
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