Reference Design For Power Supply - Quectel EM12-G Hardware Design

LTE-A Module Series
EM12-G Hardware Design
Figure 3: Power Supply Limits during Radio Transmission
To decrease voltage drop, a bypass capacitor of about 220µF with low ESR (ESR=0.7Ω) should be used,
and a multi-layer ceramic chip capacitor (MLCC) array 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 VCC pins. The main power supply from an external application has to
be a single voltage source. The width of VCC trace should be no less than 2mm. In principle, the longer
the VCC trace is, the wider it will be.
In addition, in order to get a stable power source, it is recommended to use a zener diode with reverse
zener voltage of 5.1V and dissipation power more than 0.5W. The following figure shows a reference
circuit of VCC.
VCC
Module
VCC
+
C2
C5
C1 C3 C4
D1
220uF 1uF
100nF 33pF 10pF
5.1V
Figure 4: Reference Circuit of VCC

3.3.2. Reference Design for Power Supply

Power design for the module is very important, as the performance of the module largely depends on the
power source. The power supply is capable of providing sufficient current up to 2A at least. If the voltage
drop between the input and output is not too high, it is suggested that an LDO should be used to supply
power for the module. If there is a big voltage difference between the input source and the desired output
(VCC), a buck converter is preferred to be used as the power supply.
The following figure shows a reference design for +5V input power source. The typical output of the power
supply is about 3.7V and the maximum load current is 3A.
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