Users Manual

GSM/GPRS Module Series
M66 Hardware Design
M66_Hardware_Design Confidential / Released 26 / 82
3.3.3. Reference Design For Power Supply
The power design for the module is very important, since the performance of power supply for the module
largely depends on the power source. The power supply is capable of providing the sufficient current up to
2A at least. If the voltage drop between the input and output is not too high, it is suggested to use a LDO
as module’s power supply. If there is a big voltage difference between the input source and the desired
output (VBAT), a switcher power converter is recommended to use as a power supply.
The following figure shows a reference design for +5V input power source. The designed output for the
power supply is 4.0V and the maximum load current is 3A. In addition, in order to get a stable output
voltage, a zener diode is placed close to the pins of VBAT. As to the zener diode, it is suggested to use a
zener diode whose reverse zener voltage is 5.1V and dissipation power is more than 1 Watt.
Figure 5: Reference Circuit for Power Supply
It is suggested to control the module’s main power supply (VBAT) via LDO enable pin to restart the
module when the module has become abnormal. Power switch circuit like P-channel MOSFET switch
circuit can also be used to control VBAT.
3.3.4. Monitor Power Supply
The command “AT+CBC” can be used to monitor the supply voltage of the module. The unit of the
displayed voltage is mV.
NOTE