Neo_M680 GPRS Module Hardware User Guide
Copyright © Neoway Technology Co., Ltd
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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
uH with average current ability greater than 1.2A and low DC resistance is recommended.
Figure 3-5
Reference designs of separated power supply
Other circuit
DC-DC/LDO
GPRS
module
DC-DC/LDO
Power
Input
Other circuit
DC-DC/LDO
GPRS
module
Power
Input
10 uH
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.
EMC Considerations
Place transient overvoltage protection components like TVS diode on power supply, to absorb the power
surges. SMAJ5.0A/C could be a choice.
3.1.2 VDD_EXT
It is recommended that VDD_EXT is only used for interface level transformation. VDD_EXT can output
2.8 V and 50 mA. It stops output after the module is shut down.
3.1.3 VRTC
VRTC is the external power supply pin of RTC inside the module. It can be connected to external battery or
supercapacitor. When VBAT works properly, VRTC outputs 2.8 V and maximum 2 mA and can be
connected to current limiting resistor or supercapacitor to charge. When VBAT is disconnected, the module
can discharge the battery or capacitor to supply power for RTC in short time. Leave it disconnected if not
used.
Figure 3-6shows the reference design of the VRTC power supply.
