LPWA Module Series
BG950A-GL&BG951A-GL_Hardware_Design
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Figure 18: Reference Circuit of USB Application
To ensure the integrity of USB data signals, If possible, reserve a 0 Ω resistor on USB_DP and USB_DM
traces respectively. And 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, 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.
After the module is turned off or enters PSM, do not pull up any pin of USB interface. Otherwise, the
module will have additional power consumption and may have damaged pins.
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