Product Info

LPWA Module Series
BC66-NA Hardware Design
BC66-NA_Hardware_Design 31 / 59
The following is a reference design of USB interface:
USB_DP
USB_DM
GND
USB_DP
USB_DM
GND
ESD Array
Module
PC
VUSB_3V3
3.3V
Figure 15: USB Interface Reference Design
In the circuit design of USB interface, in order to ensure the performance of USB, the following principles
are suggested in the circuit design:
 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 power supply, RF signal traces and other sensitive 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 3pF.
 Keep the ESD protection components as close to the USB connector as possible.

1. USB_MODE must be pulled down so as to realize USB download function.
2. When the USB interface is used for log capturing, the module will not be able to enter PSM.
3. When using USB function of the module, an external 3.3V power supply should be provided.
3.9. UART Interfaces
The module provides three UART ports: main UART port, debug UART port and auxiliary UART port. The
module is designed as DCE (Data Communication Equipment), following the traditional DCE-DTE (Data
Terminal Equipment) connection.
NOTES