LTE Standard Module Series
EG21-G Mini PCIe Hardware Design
EG21-G_Mini_PCIe_Hardware_Design 22 / 54
Make sure the bypass capacitor between USIM_VDD and USIM_GND is less than 1uF, and be
placed as close to (U)SIM card connector as possible. If the ground is complete on custome
rs’ 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 with parasitic
capacitance not exceeding 15pF.
The 0
Ω resistors should be added in series between the module and the (U)SIM card connector so
as 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.
3.5. USB Interface
EG21-G Mini PCIe provides one integrated Universal Serial Bus (USB) interface which complies 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 table shows the pin definition of USB interface.
Table 8: Pin Definition of USB Interface
USB_DP
USB_DM
GND
L1
Close to Module
R3
R4
Test Points
NM_0R
NM_0R
Minimize these stubs
Module
MCU
ESD Array
USB_DP
USB_DM
GND
Figure 6: Reference Circuit of USB Interface
Pin Name
Pin No.
I/O
Description
Comment
USB_DM
36
IO
USB differential data (-)
Require differential impedance of 90Ω
USB_DP
38
IO
USB differential data (+)
Require differential impedance of 90Ω
