N1_Hardware_User_Guide
Copyright © Neoway Technology Co., Ltd
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Q2: a common NPN tripolar transistor, e.g. MMBT3904; or a digital NPN tripolar transistor, e.g.
DTC123. If digital tripolar transistor is used, delete R1 and R2.
C3: 470 μF tantalum capacitor rated at 6.3V; or 1000 μF aluminum capacitor. If lithium battery is
used to supply power, C3 can be 220 μF tantalum capacitor.
Power Supply Protection
Add TVS diodes (VRWM=5 V) on the VBAT power supply, especially in automobile applications. For
some stable power supplies, zener diodes can decrease the power supply overshoot. SMF5.0AG from
ONSEMI is suggested.
PCB Trace
The trace width of primary loop lines for VBAT on PCB must be able to support the safe transmission of
2A current and ensure no obvious loop voltage reduction. Therefore, the trace width of VBAT is required
2 mm and the ground should be as complete as possible.
Separation
The module works in burst mode that generates voltage drops on power supply. Furthermore, this results
in a 217Hz TDD noise through power (One of the way of generating noise. Another way is through RF
radiation). Analog parts, especially the audio circuits, are subjected to this noise, known as a "buzz noise"
in GSM systems. To prevent other parts from being affected, use separated power supplies. The module
shall be supplied by an independent power, like a DC/DC or an LDO. See Figure 3-4.
DC/DC or LDO should output a rated peak current larger than 2 A.
The inductor used in Reference Design (b), should be a power inductor and have a very low resistance.
The value of 10 μH, with average current ability greater than 1.2A and low DC resistance, is
recommended.
Figure 3-4
Reference designs of separated power supply
Other circuit
DC-DC/LDO
N1
DC-DC/LDO
Power
Input
Other circuit
DC-DC/LDO
N1
Power
Input
10 uF
Reference design (a)
Reference design (b)
Never use a diode to make the drop voltage between a higher input and module power. Otherwise,
Neoway will not provide warranty for product issues caused by this. In this situation, the diode will
obviously decrease the module performances, or result in unexpected restarts, due to the forward voltage
of diode will vary greatly in different temperature and current.
