Product Info

Smart LTE Module Series
SC20 Hardware Design
SC20_Hardware_Design Confidential / Released
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3.4. Power Supply
3.4.1. Power Supply Pins
SC20 provides four VBAT pins dedicated to connection with the external power supply. Two VBAT_RF
pins are used for module’s RF part; two VBAT_BB pins are used for module’s baseband part.
3.4.2. Decrease Voltage Drop
The power supply range of the module is 3.5V~4.2V, and the recommended value is 3.8V. The power
supply performance, such as load capacity, voltage ripple, etc. directly influences the module’s
performance and stability. Under ultimate conditions, the module may have a transient peak current up to
3A. If the supply voltage is not enough, there will be voltage drops, and if the voltage drops below 3.1V,
the module will be turned off automatically. Therefore, please make sure the input voltage will never drop
below 3.1V.
Figure 3: Voltage Drop Sample
To decrease voltage drop, a bypass capacitor of about 100µF with low ESR (ESR=0.7Ω) should be used,
and a multi-layer ceramic chip capacitor (MLCC) should also be reserved due to its ultra-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_BB/RF 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_BB trace should be no less than 1.5mm, and the width of VBAT_RF trace should be no less than
2mm. 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 0.5W zener diode and place it
as close to the VBAT_BB/RF pins as possible. The following figure shows the star structure of the power
supply.