User's Manual

LTE Module Series
EC25-V User Manual
EC25-V_User_Manual Confidential / Released 35 /
69
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
USB_VBUS
VDD
Figure 19: Reference Circuit of USB Application
In order to meet USB data line signal integrity, components R1, R2, R3 and R4 must be placed close to
the module, and then these resistors should be placed close to each other. The extra stubs of trace must
be as short as possible.
In order to ensure the USB interface design corresponding with the USB 2.0 specification, please comply
with the following principles.
 It is important to route the USB signal traces as differential pairs with total grounding. The impedance
of USB differential trace is 90ohm.
 Do not route signal traces under crystals, oscillators, magnetic devices and RF signal traces. It is
important to route the USB differential traces in inner-layer with ground shielding on not only upper
and lower layers but also right and left sides.
 Pay attention to the influence of junction capacitance of ESD component on USB data lines. Typically,
the capacitance value should be less than 2pF.
 Keep the ESD components as close as possible to the USB connector.
EC25 module can only be used as a slave device.
NOTE