LTE Standard Module Series
EC21 Mini PCIe Hardware Design
EC21_Mini_PCIe_Hardware_Design 26 / 67
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 power supply traces.
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
EC21 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
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
