LPWA Module Series
BG77 Hardware Design
BG77_Hardware_Design 29 / 76
3.5.2. Decrease Voltage Drop
The power supply range of BG77 is from 2.6V to 4.8V. Please make sure that the input voltage will never
drop below 2.6V.
To decrease voltage drop, a bypass capacitor of about 100µF with low ESR should be used, and a
multi-layer ceramic chip capacitor (MLCC) array should also be reserved due to its low ESR. It is
recommended to use three ceramic capacitors (100nF, 33pF, 10pF) for composing the MLCC array, and
place these capacitors close to VBAT pins. The main power supply from an external application has to be
a single voltage source and can be expanded to two sub paths with star structure. The width of VBAT
trace should be no less than 1mm. In principle, the longer the VBAT trace is, the wider it will be.
In addition, in order to get a stable power source, it is suggested to use a TVS with low leakage current
and suitable reverse stand-off voltage, and also it is recommended to place it as close to the VBAT pins as
possible. The following figure shows the star structure of the power supply.
Module
VB AT
VB AT
C1
100uF
+
100nF
33pF
10pF
D1
TVS
C2 C3
C4
R1 0R
Figure 4: Star Structure of the Power Supply
3.5.3. Monitor the Power Supply
AT+CBC* command can be used to monitor the VBAT voltage value. For more details, please refer to
document [2].
NOTE
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