Product Info

Automotive Module Series
AG35 Hardware Design
AG35_Hardware_Design 52 / 129
The USB interface is recommended to be reserved for firmware upgrade in application 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
R1
R2
Test Points
ESD Array
NM_0R
NM_0R
Minimize these stubs
Module
MCU
USB_VBUS
VDD
Figure 22: Reference Circuit of USB Application
In order to ensure signal integrity of USB data lines, components R1, R2 and L1 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.
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 90Ω.
 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.
 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.
 Keep the ESD protection components as close to the USB connector as possible.
1. AG35 can be used as a slave device only.
2. “*” means under development.
NOTES