Quectel EG915U-EU Manual page 42

Voice over USB
Pin definition of the USB interface is here as follows:
Table 13: Pin Definition of USB Interface
Pin Name
USB_VBUS
USB_DP
USB_DM
For more details about the USB 2.0 specifications, please visit http://www.usb.org/home.
It is recommended to reserve test points for debugging and firmware upgrade in customers' designs. The
following figure shows a reference circuit of USB interface.
It is recommended to reserve test points for debugging and firmware upgrading in customers' designs.
Module
USB_VBUS
USB_DM
USB_DP
A common mode choke L1 is recommended to be added in series between the module and customer's
MCU in order 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. In order to ensure the integrity of USB data line signal, L1, R3 and R4
components must be placed close to the module, and also resistors R3 and R4 should be placed close to
each other. The extra stubs of trace must be as short as possible.
EG915U-EU_Hardware_Design
Pin No. I/O
8 AI
9 AIO
10 AIO
Minimize these stubs
R3
R4
USB_VBUS
L1
Close to Module
GND
Figure 18: Reference Circuit of USB Application
N
Description
USB connection detect
USB differential data (+)
USB differential data (-)
Test Points
NM_0R
NM_0R
ESD Array
LTE Standard Module Series
Comment
Typical 5.0 V
Minimum 3.5 V
USB 2.0 compliant.
Require differential
impedance of 90 Ω.
If unused, keep it open.
MCU
USB_DM
USB_DP
GND
41 / 81