User's Manual
Table Of Contents
- Copyright
- Attention
- Trademark
- Versions
- Applicable Model List
- Foreword
- Product Overview
- Structure
- Hardware Introduction
- Hardware Interface
- Electrical and Environmental Characteristic
- RF Interface
L811-EA Module Hardware User Manual Page
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5.5.2 USB Interface Application
Reference Circuit Design:
Figure 5- 6 USB Interface Reference Circuit Design
The choice of capacitance for RV101 and RV102 TVS diodes should not greater than 1pF, it is
recommended to use 0.5pF TVS diodes. There is no recommended capacitance value for RV100.
VUSB pin supplies the power for USB, the recommended power range is 3.3V ~ 4.5V. VBUS pin should
not floated or it will become the unknown device.
USB_DP and USB_DM are the high-speed differential signals, and the maximum data rate is 480Mbps.
The following requirements should be followed in case of PCB layout.
USB_DP and USB_DN signal traces should be parallel and have the equal length, avoid right angle
layout.
USB_DP and USB_DN signal traces should be wrapped with GND on both sides.
USB2.0 differential signal traces should be routed on the layer nearest to the ground plane.
Ensure the match of impedance, which is required to be 90 Ohm.
Note:
VBUS is the power for USB detection (it’s the low current signal, current value < 100uA). In circuit design,
it’s not permitted to apply VBUS power individually when the USB_DN and USB_DP are disconnected, or
the module will not go into the sleep mode.
5.6 UART Interface
5.6.1 UART Interface Description
The L811-EA module provides one 4-wire UART port. The UART1 port supports AT commands, the users
can receive and transmit AT commands through UART1.
L811-EA