User's Manual

LTE Module Series

EC25Hardware Design

EC25_Hardware_DesignConfidential / Released 41 / 90

In order to enhance the reliability and availability of the USIM card in your application, please follow the

criteria below in USIM circuit design:

 Keep layout of USIM card as close to the module as possible. Keep the trace length as less than

200mm as possible.

 Keep USIM card signals away from RF and VBAT traces.

 Assure the ground between the module and the USIM card connector short and wide. Keep thetrace

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 fromeach other and

shield them with surrounded ground.

 In order to offer good ESD protection, it is recommended to add a TVS diode array whose parasitic

capacitance should not be more than 50pF. The 22ohmresistors should be added in series between

the module and the USIM card so as to suppress EMI spurious transmission and enhance ESD

protection. The 33pFcapacitors are used for filtering interference of GSM900.Please note that the

USIM peripheral circuit should be close to the USIM card connector.

 The pull-up resistor on USIM_DATA line can improve anti-jamming capability when long layout trace

and sensitive occasion areapplied, and should be placed close to the USIM card 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 communication, data transmission, GNSS NMEA sentences output, software

debugging, firmware upgrade and voice over USB*. The following table shows the pin definition of USB

interface.

Table 10: Pin Description of USB Interface

Pin Name Pin No. I/O Description Comment

USB Signal Part

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

For more details about the USB 2.0 specifications, please visithttp://www.usb.org/home