User's Manual

LTE Module Series
EC25-V User Manual
EC25-V_User_Manual Confidential / Released 34 /
69
criteria below in the USIM circuit design:
 Keep layout of USIM card as close as possible to the module. Assure the length of trace is less than
200mm.
 Keep USIM card signal away from RF and VBAT alignment.
 Assure the ground between the module and the USIM connector short and wide. Keep the width of
ground and USIM_VDD no less than 0.5mm to maintain the same electric potential.
 To avoid cross-talk between USIM_DATA and USIM_CLK, keep them away with each other and
shield them with surrounded ground.
 In order to offer good ESD protection, it is recommended to add TVS which parasitic capacitance
should not be more than 50pF. The 22ohm resistors should be added in series between the module
and the USIM card so as to suppress the EMI spurious transmission and enhance the ESD
protection. The 33pF capacitors are used for filtering interference of GSM900. Please note that the
USIM peripheral circuit should be close to the USIM connector.
 The pull-up resistor on USIM_DATA line can improve anti-jamming capability when long layout trace
and sensitive occasion are applied, and should be placed close to the USIM connector.
3.10. USB Interface
EC25 contains one integrated Universal Serial Bus (USB) transceiver which complies with the USB 2.0
specification and supports high-speed (480Mbps) and full-speed (12Mbps) modes. The USB interface is
used for AT command, data transmission, GNSS NMEA sentences output, software debug and firmware
upgrade. The following table shows the pin definition of USB interface.
Table 10: USB Pin Description
Pin Name
Pin No.
I/O
Description
Comment
USB_DP
69
IO
USB differential data bus (positive).
Require differential
impedance of 90Ω.
USB_DM
70
IO
USB differential data bus (minus).
Require differential
impedance of 90Ω.
USB_VBUS
71
PI
Used for detecting the USB
connection.
Typical 5.0V
GND
72
Ground
More details about the USB 2.0 specifications, please visit http://www.usb.org/home.
The USB interface is recommended to be reserved for firmware upgrade in your design. The following
figure shows the reference circuit of USB interface.