Product Info

Smart LTE Module Series
SC20 Hardware Design
SC20_Hardware_Design 37 / 130
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 to increase voltage surge withstand capability. The
following figure shows the star structure of the power supply.
Module
VBAT_RF
VBAT_BB
VBAT
C1
100uF
C6
100nF
C7
33pF
C8
10pF
+
+
C2
100nF
C5
100uF
C3
33pF
C4
10pF
D1
Figure 4: Star Structure of the Power Supply
3.4.3. Reference Design for Power Supply
The power design for the module is very important, as the performance of module largely depends on the
power source. The power supply of SC20 should be able to provide sufficient current up to 3A at least. If
the voltage drop between the input and output is not too high, it is suggested to use an LDO to supply
power for the module. If there is a big voltage difference between the input source and the desired output
(VBAT), a buck converter is preferred to be used as the power supply.
The following figure shows a reference design for +5V input power source which adopts an LDO
(MIC29302WU) from MICREL. The typical output voltage is 3.8V and the maximum load current is 3.0A.
DC_IN
C1
C2
MIC29302WU U1
IN
OUT
EN
GND
ADJ
2 4
1 3 5
VBAT
100nF
C3
470uF
C4
100nF
R2
100K
47K
R3
470uF
470R
51K
R4
R1
1%
1%
Figure 5: Reference Circuit of Power Supply