LTE-A Module Series
EG18 Hardware Design
EG18_Hardware_Design 37 / 104
3.5.2. Decrease Voltage Drop
The power supply range of the module is from 3.3V to 4.3V. Please make sure the input voltage will never
drop below 3.3V. The following figure shows the maximum voltage drop when burst transmission occurs
during radio transmission in 3G and 4G networks.
VCC
Max Tx Power
Min. 3.3V
Ripple
Drop
Max Tx Power
Figure 8: Power Supply Limits during Tx Power
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 of the MLCC array,
and to place these capacitors close to 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 should be.
In addition, in order to get a stable power source, it is suggested to use a zener diode of which reverse
zener voltage is 5.1V and dissipation power is more than 0.5W. The following figure shows the star
structure of the power supply.
Module
VBAT_RF
VBAT_BB
VBAT
C1
100
μ
F
C7
100nF
C8
33pF
C9
10pF
+
+
C2
100nF
C5
100
μF
C3
33pF
C4
10pF
D1
5.1V
+
C6
100
μ
F
Figure 9: Star Structure of the Power Supply