Neo_M660A GPRS Module Hardware User Guide
Copyright © Neoway Technology Co., Ltd
11
Figure 3-4
Reference design of power supply controlled by p-MOSFET
VCC_IN_3.9V
VBAT
10K
100K
33 pF
10 uF
GPRS_EN
2K
10K
0.1 uF
Q1
R4
C1
C2
C4
C5
C7
R1
R2
10 uF 0.1 uF
R3
Q2
TVS
5V
470 uF
C3
C6
100pF
S
G
D
In Figure 3-4, the module is powered on when GPRS_EN is set to high level.
Q2 is added to eliminate the need for a high enough voltage level of the host GPIO. In case that the 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 automobile
applications. For some stable power supplies, zener diodes can decrease the power supply overshoot.
MMSZ5231B1T1G from ONSEMI and PZ3D4V2 from Prisemi are options.
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 decrease. Therefore, the trace width of VBAT loop line is
required at least 2 mm and the ground should be as complete as possible.
