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Smart Module Series
3.4.2. Voltage Stability Requirements
The power supply range of the module is 3.50–4.20 V, and the recommended value is 3.80 V. The power
supply performance, such as load capacity, voltage ripple, etc. directly influences the module's
performance and stability. Under ultimate conditions, the transient peak current of the module may surge
up to 3 A. If the power supply capacity is not sufficient, there will be the risk that the voltage drops below
3.25 V and as a result the module powers off automatically. Therefore, please ensure the input voltage
will never drop below 3.25 V.
3 A
Module input current
3.80 V
Voltage
3.25 V
Figure 3: Voltage Drop Sample
To ensure that the supply voltage of the module will not drop below 3.25 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_BB/VBAT_RF pins. Additionally,
add a 4.7 μF capacitor in parallel. 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 3 mm. In principle, the longer the VBAT trace is, the wider it should be. Additionally, the
ground plane of the power supply part should be as complete as possible.
In addition, in order to get a stable power source, it is suggested to use a TVS diode of at least 500 W and
place it as close to the VBAT_BB/VBAT_RF pins as possible to enhance surge protection. The following
figure shows the star structure of the power supply.
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