Users Manual

LTE Standard Module Series
EC25 Hardware Design
EC25_Hardware_Design
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In order to enhance the reliability and availability of the (U)SIM card in customers’ applications, please
follow the criteria below in (U)SIM circuit design:
Keep placement of (U)SIM card connector to the module as close as possible. Keep the trace length
as less than 200mm as possible.
Keep (U)SIM card signals away from RF and VBAT traces.
Make sure the bypass capacitor between USIM_VDD and USIM_GND less than 1μF, and place it as
close to (U)SIM card connector as possible. If the ground is complete on customers’ PCB,
USIM_GND can be connected to PCB ground directly.
To avoid cross-talk between USIM_DATA and USIM_CLK, keep them away from each 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 15pF. The 0Ω resistors should be added in series between the
module and the (U)SIM card to facilitate debugging. The 33pF capacitors are used for filtering
interference of EGSM900. Please note that the (U)SIM peripheral circuit should be close to the
(U)SIM card 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 (U)SIM card connector.
3.10. USB Interface
EC25 contains one integrated Universal Serial Bus (USB) interface which complies with the USB 2.0
specification and supports high-speed (480Mbps) and full-speed (12Mbps) modes. The USB interface
can only serves as a slave device and 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_DP 69 IO USB differential data bus (+)
Require differential
impedance of 90Ω
USB_DM 70 IO USB differential data bus (-)
Require differential
impedance of 90Ω
USB_VBUS 71 PI
USB connection detectionUSB
detection
Typical 5.0V
GND 72 Ground