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FIBOCOM SC138-
NA
Series Hardware Guide
37/88
Recommended
Capacitance
Application
Description
1uF, 100nF
Filter capacitance
Filter out the interference caused by clock and
digital signal.
39pF, 33pF, 18pF, 8.2pF,
6.8pF
Decoupling
capacitance
Filter out high-frequency interference.
3.1.2
VRTC
VRTC supplies power for the RTC clock inside the module. When the VBAT power supply of the module
is powered on, VRTC will output voltage; otherwise, it is powered by external power supply (for example,
button battery) if the real-time clock needs to be maintained. VRTC parameters are shown in the
following table:
Table 3-3 VRTC parameters
Parameters
Minimum
Value
Typical
Value
Maximum
Value
Unit
VRTC output voltage
2.5
3.1
3.2
V
VRTC input voltage (normal clock)
2.0
3.0
3.25
V
VRTC input current (normal clock)
-
8
-
uA
If VRTC power supply is powered by external battery, the reference circuit is shown in the following
figure:
M odule
V R T C
+
C oin cell