UMTS/HSPA Module Series
UG96 Hardware Design
UG96_Hardware_Design 42 / 76
used for AT command communication, data transmission, software debugging and firmware upgrade. The
following table shows the pin definition of USB interface.
Table 13: Pin Definition of USB Interface
Pin Name
Pin No. I/O
Description
Comment
USB_DP
9
IO
USB differential data bus (+)
Require differential
impedance of 90Ω.
USB_DM
10
IO
USB differential data bus (-)
Require differential
impedance of 90Ω.
USB_VBUS
8
PI
USB detection
2.5V~5.25V.
Typically 5.0V.
For more details about the USB 2.0 specification, please visit http://www.usb.org/home.
The following figure shows a reference circuit of USB interface.
Module
USB_VBUS
USB_DP
USB_DM
GND
USB connector
Close to USB connector
Differential layout
USB_VBUS
USB_DP
USB_DM
GND
NM_2pF
ESD
NM NM
Rs
Rs
Figure 25: Reference Circuit of USB Interface
The following principles should be complied with when design the USB interface, so as to meet USB 2.0
specification.
⚫
It is important to route the USB signal traces as differential pairs with total grounding. The impedance
of USB differential trace is 90
Ω.
⚫
Pay attention to the influence of junction capacitance of ESD protection components on USB data
lines. Typically, the capacitance value should be less than 2pF.
⚫
Do not route signal traces under crystals, oscillators, magnetic devices or 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.
⚫
Keep the ESD protection components as close to the USB connector as possible.