Product Info
LTE Standard Module Series
EC25 Series Hardware Design
EC25_Series_Hardware_Design 49 / 126
⚫ Keep placement of (U)SIM card connector to the module as close as possible. Keep the trace length
as less than 200 mm 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 1 μF, 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 15 pF. The 0 Ω resistors should be added in series between the
module and the (U)SIM card to facilitate debugging. The 33 pF 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 (480 Mbps) and full-speed (12 Mbps) modes. The USB interface
can only serve 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
For more details about the USB 2.0 specifications, please visit http://www.usb.org/home.
The USB interface is recommended to be reserved for firmware upgrade in customers’ designs. The
following figure shows a reference circuit of USB interface.
Pin Name
Pin No.
I/O
Description
Comment
USB_DP
69
IO
USB differential data bus (+)
Require differential
impedance of 90 Ω
USB_DM
70
IO
USB differential data bus (-)
Require differential
impedance of 90 Ω
USB_VBUS
71
PI
USB connection detectionUSB
detection
Typical 5.0 V
GND
72
Ground