N723-EA Hardware User Guide
Chapter 5 Application Interfaces
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40
USB_DP
42
IO
USB data positive signal
download and data transmission. DM and
DP adopt differential routing, and the
differential impedance must be 90
Ω.
USB_ID
43
DI
USB ID pin
Used for OTG function.
Leave this pin floating if it is not used.
N723-EA can implement program download, data communication, and debugging through the USB
interface. The module's USB is as a slave device by default. Figure 5-18 shows the recommended
USB connection circuit.
Figure 5-18
Reference USB connection design
R1
N723-EA
Module
USB_VBUS
USB_DM
USB_DP
GND
USB Host
USB_DM
USB_DP
GND
R2
D2
D3
D1
C1
C2
VCC(5.0V)
Schematic Design Guidelines:
⚫
Connect a 1 μF (C1) and a 33 Pf (C2) filter capacitors in parallel to the USB_VBUS pin. An ESD
component must be added for the power cable.
⚫
The junction capacitance of the ESD components D2 and D3 on the USB_DP and USB_DM
data lines must be smaller than 0.5 pF.
⚫
Connecting a resistor less than 10 Ω in series to each of the USB_DP and USB_DM cables can
effectively improve the ESD performance of the USB.
PCB Design Guidelines:
⚫
Place the filter capacitor on the USB_VBUS as close as possible to the module pins, and place
the ESD component as close as possible to the USB connector.
⚫
Place the ESD component on the USB_DP and USB_DM as close to the USB connector as
possible.
⚫
USB data lines must adopt differential routing, and the differential impedance must be 90 Ω. The
cable from the port to the module must be isolated from other signal cables and must be
wrapped by ground cables.