WM620 Hardware User Guide
V1.1
All rights reserved by Shenzhen Neoway Technology Co., Ltd.
Page 10
Note
：
SIM card is very sensitive to RF interference.
Serious RF interference to SIM card will cause the WM620 to miss the detection to SIM card and out of service.
So, it is very importance in the PCB design listed as the following message.
The antenna should be installed a long distance away from the SIM card and SIM card traces.
The SIM card traces should be routed as short as possible and shielded with GND copper.
The ESD diodes or capacitors should be placed closed to SIM card.
2.5 USB Interface
Table 2-3, USB Interface
Pin
Pin Name
I/O
Function description
Note
18
USB D+
I/O
High-speed USB differential data, (+)
19
USB D-
I/O
High-speed USB differential data, (-)
20
V_USB
PWR
USB Power
Input voltage 3.3 to 5.5V.
The WM620 module is compliant with USB2.0 full speed device. The USB2.0 specification requires the hosts
such as PCs to support three USB speeds, namely low-speed (1.5Mbps), full-speed (12Mbps) and high-speed
(480Mbps).
The V_USB pin is an analog input. A
4.7µF
decoupling MLCC capacitor to GND is strongly recommended,
and should be placed as closely as possible to V_USB Pin. It will increase the USB stability. ESD diodes
should be installed to these three signals. Shown in Figure 2-10.
Figure 2-10
Note:
The layout design of this USB should comply with the USB 2.0.
The traces of USB_D+ and USB_D- must be routed as a group of differential pair with
90Ω
differential
impedance.
The USB differential pair should be routed side-by-side and on the same layer.
USB_D+ and D- is a pair of high speed signals, so the trace lengths should match as well as possible.
