N10_Hardware_User_Guide
Copyright © Neoway Technology Co., Ltd.
Q2 is added to eliminate the need for a high enough voltage level of the host GPIO. In case GPIO can
output a high voltage greater than VCC_IN_3.9V - |V
GS(th)
|, where V
GS(th)
is the Gate Threshold Voltage,
Q2 is not needed.
Reference components:
Q1 can be IRML6401 or Rds(on) p-MOSFET which has higher withstand voltage and drain current.
Q2: a common NPN transistor, e.g. MMBT3904; or a digital NPN transistor, e.g. DTC123. If digital
transistor is used, delete R1 and R2.
C3: 470 μF tantalum capacitor rated at 6.3 V; or 1000 μF aluminum capacitor. If lithium battery is
used to supply power, C3 can be 220 μF tantalum capacitor.
Protection
Place a TVS diode (V
RWM
=5 V) on the VBAT power supply to ground, especially in automotive
applications. For some stable power supplies, zener diodes can decrease the power supply overshoot.
SMF5.0AG from ONSEMI is an option.
Line Rules
The width of primary loop lines for VBAT on PCB must be able to support the safe transmission of 2 A
current and ensure no obvious loop voltage decrease. Therefore, the loop line width of VBAT is required 2
mm and the ground should be as complete as possible.
Separation
The GPRS module works in burst mode that generates voltage drops on power supply. Furthermore this
results in a 217 Hz TDD noise through power (One of the way 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, it's better to use separated power
supplies. The module shall be supplied by an independent power, like a DC/DC or LDO. See Figure 3-5.
DC/DC or LDO should output 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.
10 μH with average current ability greater than 1.2 A and low DC resistance is recommended.
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