CC3120 Datasheet, PDF (47/57 Pages) Texas Instruments – SimpleLink Wi-Fi Wireless Network Processor Internet-of-Things Solution for MCU Applications

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CC3120
SWAS034 – FEBRUARY 2017
6.2.4 Digital Input and Output
The following guidelines are for the digital I/O.
• Route SPI and UART lines away from any RF traces.
• Keep the length of the high-speed lines as short as possible to avoid transmission line effects.
• Keep the line lower than 1/10 of the rise time of the signal to ignore transmission line effects. This is
required if the traces cannot be kept short. Place the resistor at the source end, closer to the device
that is driving the signal.
• Add series-terminating resistor for each high-speed line (such as SPI_CLK or SPI_DATA) to match the
driver impedance to the line. Typical terminating-resistor values range from 27 to 36 Ω for a 50-Ω line
impedance.
• Route high-speed lines with a ground reference plane continuously below it to offer good impedance
throughout. This routing also helps shield the trace against EMI.
• Avoid stubs on high-speed lines to minimize the reflections. If the line must be routed to multiple
locations, use a separate line driver for each line.
• If the lines are longer compared to the rise time, add series-terminating resistors near the driver for
each high-speed line to match the driver impedance to the line. Typical terminating-resistor values
range from 27 to 36 Ω for a 50-Ω line impedance.
6.2.5 RF Interface
The following guidelines are for the RF interface. Follow guidelines specified in the vendor-specific
antenna design guides (including placement of the antenna). Also see CC3120 and CC3220 SimpleLink™
Wi-Fi^® and IoT Solution Layout Guidelines for general antenna guidelines.
• Ensure that the antenna is matched for 50-Ω. A Pi-matching network is recommended.
• Ensure that the area underneath the BPF pads are grounded on layer one and layer two, and that the
minimum fulter requirements are met.
• Verify that the Wi-Fi RF trace is a 50-Ω, impedance-controlled trace with a reference to solid ground.
• The RF trace bends must be made with gradual curves, and 90-degree bends must be avoided.
• The RF traces must not have sharp corners.
• There must be no traces or ground under the antenna section.
• The RF traces must have via stitching on the ground plane beside the RF trace on both sides.
Copyright © 2017, Texas Instruments Incorporated
Applications, Implementation, and Layout
47
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