LTE Module Series
EC25 Mini PCIe Hardware Design
EC25_Mini_PCIe_Hardware_Design Confidential / Released 20 / 42
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 whose parasitic capacitance
should not be more than 50pF. The 22 ohm resistors should be added in series between the module
and the USIM card so as to suppress EMI spurious transmission and enhance 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 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 USIM card connector.
3.5. USB Interface
The following table shows the pin definition of USB interface.
Table 7: Pin Definition of USB Interface
EC25 Mini PCIe is compliant with USB 2.0 specification. It can only be used as a slave device. Meanwhile,
it supports high speed (480Mbps) mode and full speed (12Mbps) mode. The USB interface is used for AT
command communication, data transmission, GNSS NMEA output, software debugging, firmware
upgrade and voice over USB*. The following figure shows a reference circuit of USB interface.
USB_DP
USB_DM
GND
USB_DP
USB_DM
GND
R1
R2
Close to Module
R3
R4
Test Points
ESD Array
NM_0R
NM_0R
0R
0R
Minimize this stub
Module
MCU
Figure 5: Reference Circuit of USB Interface
USB differential data (-)
Require differential impedance of 90Ω
USB differential data (+)
Require differential impedance of 90Ω
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