Quectel EM05-G Hardware Design page 41

Module
USB_DM
USB_DP
GND
A common mode choke L1 is recommended to be added in series between the module and customer's
MCU to suppress EMI spurious transmission. Meanwhile, the 0 Ω resistors (R3 and R4) should be added
in series between the module and the test points to facilitate debugging, and the resistors are not
mounted by default. To ensure the integrity of USB data line signal, L1, R3 and R4 components must be
placed close to the module, and also these resistors should be placed close to each other. The extra
stubs of trace must be as short as possible.
To meet USB 2.0 specification, the following principles should be complied with when designing the USB
interface.
Route the USB signal traces as differential pairs with ground surrounded. The impedance of USB
⚫
differential trace is 90 Ω.
⚫ Do not route signal traces under crystals, oscillators, magnetic devices, PCIe and RF signal traces.
Route the USB differential traces in inner-layer of the PCB, and surround the traces with ground on
that layer and with ground planes above and below.
⚫ Pay attention to the influence of junction capacitance of ESD protection components on USB data
lines. Typically, the capacitance value should be less than 2 pF.
⚫ Keep the ESD protection components as close to the USB connector as possible.
EM05-G_Hardware_Design
Minimize these stubs
ESD Array Close to Module
Figure 18: Reference Circuit of USB 2.0 Interface
Test Points
NM_0R
R3
NM_0R
R4
L1
LTE Standard Module Series
EM05-G Hardware Design
MCU
USB_DM
USB_DP
GND
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