Product Info

Automotive Module Series
AG35 Hardware Design
AG35_Hardware_Design 42 / 129
157, 158, 167, 174,
177, 178, 181, 184,
187, 191, 196~299
3.6.2. 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 voltage drop during burst transmission in 2G network.
The voltage drop will be less in 3G and 4G networks.
VBAT
Burst
Transmission
Min.3.3V
Ripple
Drop
Burst
Transmission
Figure 8: 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 capacitor (MLCC) array should also be reserved due to its low ESR. It is
recommended to use three ceramic capacitors (100nF, 33pF, 10pF) for composing the MLCC array, and
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 will be.
In addition, in order to get a stable power source, it is suggested to use a power TVS ( e.g. WS4.5DPF-B,
V
RWM
=4.5V, Ppp=450W) and a zener diode with dissipation power more than 0.5W, and place them as
close to the VBAT pins as possible. The following figure shows the star structure of the power supply.
Module
VBAT_RF
VBAT_BB
VBAT
C1
C6 C7 C8
10pF
+
+
C2
C6
100uF
C3 C4
D1
100nF
33pF
10pF
33pF100nF
100uF
D2
Figure 9: Star Structure of the Power Supply