LTE-A Module Series
EG060V-EA Hardware Design
EG060V-EA_Hardware_Design 41 / 82
For more details about the specifications of USB 2.0, please visit this website down below:
https://www.usb.org/document-library/usb-20-specification.
It is recommended to reserve in your designs the USB interface for firmware upgrades. Below is a
reference design of USB 2.0 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 these stubs
Module
MCU
USB_VBUS
VDD
USB_ID*
GPIO
Figure 20: Reference Design of USB Interface
In order to ensure the signal integrity of USB data lines, R1, R2, R3 and R4 should be placed close to the
module as well as to each other. The extra stubs of trace must be as short as possible.
To meet USB 2.0 specifications, the following principles should be complied with while designing the USB
interface:
⚫
It is important to route the USB signal traces as a differential pair with total grounding. Keep the
impedance of the pair at
90 Ω.
⚫
Do not route signal traces under crystals, oscillators, magnetic devices, PCIe and RF signal traces.
Route the USB differential traces in inner-layers of the PCB, and surround the traces with ground on
the same layer and with ground planes on adjacent layers.
⚫
Pay attention to the influence of junction capacitance of ESD protection components on USB data
traces. Typically, the capacitance value of ESD protection components should be less than 2.0 pF for
USB 2.0.
⚫
Keep the ESD protection components as close to the USB connector as possible.
⚫
If possible, reserve a 0 ohm resistor on USB_DP and USB_DM lines respectively.