Vrtc Interface - Quectel SC690A Series Hardware Design

VBAT
PWRKEY
Others

3.4. 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 capacitor according to application demands. The following figure shows the reference circuit when an
external battery is utilized for powering RTC.
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When VBAT is disconnected, the recommended input voltage range for VRTC is 2.0–3.25 V and the
recommended typical value is 3.0 V.
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When powered by VBAT, the RTC error is 50 ppm. When powered by VRTC, the RTC error is about
200 ppm.
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If a rechargeable battery is used, ESR of the battery should be less than 2 kΩ.
If RTC function is not needed, it is recommended to connect a 0.1 μF capacitor to VRTC.
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SC690A_Series_Hardware_Design
> 8 s
Figure 10: Timing of Turning off Module
C
Figure 11: RTC Powered by Coin Cell
Power down
VRTC
RTC
Core
Coin Cell
Module
Smart Module Series
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