Quectel SC690A Series Hardware Design page 40

Smart Module Series
up to 3 A. If the power supply capability is not sufficient, there will be voltage drops, and if the voltage
drops below 3.1 V, the module will power off automatically. Therefore, ensure that the input voltage
never drops below 3.1 V.
3A
Input current
3.8V
Voltage
Figure 5: Voltage Drop Sample
To prevent the voltage from dropping below 3.1 V, use a bypass capacitor of about 100 µF with low ESR
(ESR = 0.7 Ω), and reserve a multi-layer ceramic chip capacitor (MLCC) array due to its ultra-low ESR. It
is recommended to use three ceramic capacitors (100 nF, 33 pF, 10 pF) to compose the MLCC array,
and place these capacitors close to VBAT pins. Additionally, add a 4.7 µF capacitor in parallel. The width
of VBAT trace should be no less than 3 mm. In principle, the longer the VBAT trace is, the wider it should
be.
In addition, to get a stable power source, it is suggested to use a 2000 W TVS and place it as close to
the VBAT pins as possible to enhance surge protection.
The following figure shows the structure of the power supply.
VBAT
VBAT
+
C5
C3 C4
C2
C1
D1
Module
100 μF 4.7 μF 100 nF 33 pF 10 pF
GND
Figure 6: Structure of Power Supply
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