In order to prevent the damage of the module caused by surge and overvoltage, it is
suggested that a 5.1V/500mW zener diode to be connected on the module VBAT pin.
It is suggested that 3 ceramic capacitors (33pF, 10pF, 100nF) to be added to the VBAT pin
and to be placed close to the VBAT pin.
The minimum operating voltage of the module is 3.3V, because the transmission data or
GSM call will produce more than 2A current, resulting in the power supply voltage ripple
voltage drop, so the power supply voltage shall not be less than 3.3V.
GSM TDMA burst current supply voltage drop
3.4 USB port
The module USB port supports USB2.0 high-speed protocol, supports slave device mode, and
does not support USB charging mode. The USB input / output routing needs to follow the
USB2.0 characteristic, and the USB interface is defined as follows:
PIN
Signal
IO
Description
36
USB_D-
IO
USB differential signal-
38
USB_D+
IO
USB differential
Circuit diagram of USB connection
NOTE:
USB routing design needs to strictly comply with the requirements of the USB2.0 protocol,
note the protection of the data line, differential line, controlling impedance for the line is 90
ohm. The ESD protection device should be added on the data line, and the equivalent
capacitance value of the ESD protection device is less than 1pF.
The power supply voltage of the USB bus is provided inside the module without external
supply. At the same time, the USB bus is not provided power. Because of the power of
module can only be used as slave device of USB bus.
USB port supports following functions:
Software download and update
Data communication
AT command
