Decrease Voltage Drop - Quectel UC200T-EM Hardware Design

56, 72, 85~112

3.5.2. Decrease Voltage Drop

The power supply range of the module is from 3.4V to 4.3V. Please make sure that the input voltage will
never drop below 3.4V. The following figure shows the voltage drop during burst transmission in 2G
network. The voltage drop will be less in 3G networks.
VBAT
Min.3.3V
Figure 3: Power Supply Limits during Burst Transmission
To decrease voltage drop, a bypass capacitor of about 100µF with low ESR should be used, and a
multi-layer ceramic chip (MLCC) capacitor 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 the VBAT 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 1mm; 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 that a TVS diode WS4.5D3HV of which
reverse stand-off voltage is 4.7V and peak pulse power is up to 2550 Watts should be used. The following
figure shows the star structure of the power supply.
VBAT
D1
WS4.5D3HV
UC200T-EM_Hardware_Design
Burst
Transmission
+
C3 C4
C2
C1
100nF 33pF 10pF
100uF
Figure 4: Star Structure of the Power Supply
Burst
Transmission
Drop
+
C5
C6 C7 C8
100uF 100nF 33pF 10pF
UMTS/HSPA(+) Module Series
UC200T-EM Hardware Design
Ripple
VBAT_RF
VBAT_BB
Module
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