Service Guide

LTE Standard Module Series
EG915U_Series_Hardware_Design 43 / 90
Table 13: Pin Definition of USB Interface
For more details about the USB 2.0 specifications, visit http://www.usb.org/home.
Reserve test points for debugging and firmware upgrade in your design. The following figure shows a
reference circuit of USB interface.
USB_DP
USB_DM
GND
USB_DP
USB_DM
GND
L1
Close to Module
R3
R4
Test Points
ESD Array
NM_0R
NM_0R
Minimize these stubs
Module
MCU
USB_VBUS
USB_VBUS
Figure 19: Reference Circuit of USB Application
A common mode choke L1 is recommended to be added in series between the module and your 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 so as to facilitate debugging, and the resistors are not mounted
by default. To ensure the signal integrity of USB data lines, L1, R3, and R4 must be placed close to the
module, and resistors R3 and R4 should be placed close to each other. The extra stubs of trace must be
as short as possible.
When designing the USB interface, you should follow the following principles to meet USB 2.0
specification.
⚫ 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 or near crystals, oscillators, magnetic devices, and RF signal traces.
Route the USB differential traces in inner-layer of the PCB, and surround the traces with ground on
Pin Name
Pin No.
I/O
Description
Comment
USB_VBUS
8
AI
USB connection detect
Typ. 5.0 V
Min. 3.5 V
USB_DP
9
AIO
USB differential data (+)
USB 2.0 compliant.
Requires differential impedance of 90 Ω.
If unused, keep them open.
USB_DM
10
AIO
USB differential data (-)