LPWA Module Series
BG950A-GL&BG951A-GL_Hardware_Design
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It is recommended to reserve test points for debugging and firmware upgrading in customers’ designs.
Figure 16: Reference Circuit of USB Application
To ensure the integrity of USB data trace signal, resistors R1 and R2 should be placed close to the
module, and 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, comply with the following principles while designing the USB interface.
It is important to 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.
It is important to 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.
Junction capacitance of the ESD protection device might cause influences on USB data traces, so
pay attention to the selection of the device. Typically, the stray capacitance should be less than
2 pF .
Keep the ESD protection devices as close to the USB connector as possible.
If possible, reserve a 0 Ω resistor on USB_DP and USB_DM traces respectively.
For more details about the USB specifications, visit http://www.usb.org/home.
