LTE-A Module Series
EM121R-GL Hardware Design
EM121R-GL Hardware Design 28 / 80
3.3.1. Decrease Voltage Drop
The power supply range of the module is from 3.135 V to 4.4 V. Please ensure that the input voltage will
never drop below 3.135 V, otherwise the module will be powered off automatically. The following figure
shows the maximum voltage drop during radio transmission in 3G/4G networks.
Power Supply
Burst Transmission
Ripple
≤ 100 mV
Burst Transmission
Drop
VBAT
≥
3.135 V
Figure 5: Power Supply Limits during Radio Transmission
Ensure the continuous current capability of the power supply is 2.0 A.
To decrease the voltage drop, two
bypass capacitor of about 220
µF with low ESR (ESR = 0.7 Ω) should be used. To decrease the power
supply is disturbed, a multi-layer ceramic chip capacitor (MLCC) array also should be used due to its
ultra-low ESR. It is recommended to use four ceramic capacitors (1 µF, 100 nF, 33 pF, 10 pF) for
composing the MLCC array, and place these capacitors close to VCC pins. The width of VCC trace
should be no less than 2.5 mm. In principle, the longer the VCC trace is, the wider it should be.
In addition, to guarantee stability of the power supply, please use a zener diode with a reverse zener
voltage of 5.1 V and a dissipation power of higher than 0.5 W. The following figure shows a reference
circuit for the VCC.
Module
ET
2, 4
C2
220
μ
F
3, 5, 11
VCC (3.7 V Typ.)
VCC
GND
C10
10 pF
C8
33 pF
C6
100 nF
C4
1
μ
F
+
C1
220
μ
F
D1
5.1 V
VCC
GND
C9
10 pF
C7
33 pF
C5
100 nF
C3
1
μ
F
+
27, 33, 39,
45, 51, 57,
71, 73
70, 72, 74
PMU
Figure 6: Reference Circuit for the VCC