Silicon Laboratories AN1342 User manual

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AN1342: RS9116 CC1 Board Layout Guidelines
Version 1.1
August 20, 2021

AN1342: RS9116 CC1 Board Layout Guidelines
Version 1.1
silabs.com | Building a more connected world. 2| Page
Table of Contents
1Introduction..................................................................................................................................................................3
2Placement Guidelines.................................................................................................................................................4
3Antenna Layout Guidelines........................................................................................................................................5
4SDIO/SPI Layout Guidelines.......................................................................................................................................7
5USB Layout Guidelines...............................................................................................................................................9
6UART Layout Guidelines ..........................................................................................................................................10
7Power Supply Layout Guidelines ............................................................................................................................11
8GND Layout Guidelines ............................................................................................................................................13
9Revision History........................................................................................................................................................15

AN1342: RS9116 CC1 Board Layout Guidelines
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1 Introduction
This Application Note provides PCB layout guidelines for the RS9116 CC1 module. These guidelines cover parts placement,
various critical traces routing like RF, Host interfaces routing like SDIO/SPI, USB, UART, power routing, and GND pour.
CC1 module placement and routing can be done within 4-layer PCB stack-up. However, designers can choose higher
number of layers, based on product needs. This document describes placement and routing considering a 4-layer stack-up
setup.
Below is the recommended layer stack-up and placement/routing considering a 4-layer stack-up. Exact PCB thickness can
be as per the layer stack-up provided by the PCB manufacturer. It is recommended to use a PCB thickness close to 1.6
mm, but designers can choose suitable thickness based on product needs.
•Layer 1: Parts Placement, Interface signals (SDIO/SPI, USB, UART)
•Layer 2: GND
•Layer 3: Power supply star routing
•Layer 4: Power supply star routing, USB & UART Interface signals and GPIOs

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2 Placement Guidelines
Here are the recommendations for the placement of the CC1 module and its associated parts. Parts are placed on the same
side of the CC1 module, in this Application Note. However, designers can choose to place them on either side of PCB for
achieving best placement and routing. Designers can use suitable antenna as per the product needs, like on-board PCB
trace, External PCB trace, Dipole, etc. The following steps can be sequentially followed to achieve optimal placement.
1. To get the best RF performance from CC1 circuitry and antenna, it is recommended to place the module near the
PCB edge. Antenna part guidelines must be followed for its placement and routing.
2. Decoupling capacitors are recommended to be placed on intended power pins. Decaps must be placed within 5
mm distance from the module pins.
3. VIN_3P3 Capacitor should be placed within 10mm distance from the module pin.
4. Series resistor on Clock signal of SPI or SDIO interface, must be placed close to the source of this clock signal.
It must not be placed near the module end of the signal.
Considering the above recommendations, the CC1 module and its circuitry can be placed on single side of PCB as shown
below. This takes 20 mm x 20 mm of board space approximately. Designers can choose to place the components
different from the below recommendation to suit the product needs.
Figure 1: CC1 Module and Components Placement
Antenna Keep out
Area, Etch the
'GND' plane
underneath the
Keep-out area in
all layers
VIN_3P3
Cap
RS9116-
CC1

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3 Antenna Layout Guidelines
The CC1 module has an integrated PCB trace antenna, and it works at both 2.4 GHz and 5 GHz. This antenna must be
positioned toward outer periphery of the PCB edge. There is also a U.FL connector on the module, through which an external
antenna can be connected. The choice between the on-board antenna and the external antenna can be made through a
software command. The guidelines below must be followed to get best RF performance from the PCB antenna and antenna
connected to U.FL connector.
1. There should be no metal planes or traces in the region under the PCB antenna and beside it for at least 3 mm.
The module should be placed such that the antenna portion is on the edge of the PCB. The figure below may be
used as a reference.
Figure 2: PCB Antenna Layout Requirement
2. The figures below show the U.FL connector integrated on the module and mating connector with external antenna.
The connector on the external antenna should be pushed down to fit into the U.FL connector connected to the
module.

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Figure 3: U.FL Connector Details

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4 SDIO/SPI Layout Guidelines
SDIO and SPI are high speed interfaces where-in clock signals can reach up to 100 MHz. High speed design guidelines
like below must be followed for the signals in these interfaces. SDIO/SPI signals include SDIO_CLK/SPI_CLK,
SDIO_CMD/SPI_CSN, SDIO_D0/SPI_MOSI, SDIO_D1/SPI_MISO, SDIO_D2/SPI_INTR, SDIO_D3.
1. The characteristic impedance of the SDIO/SPI lines should be 50 Ω.
2. Match the lengths of all SDIO/SPI lines within 100 mils tolerance.
3. Keep the SDIO_CLK/SPI_CLK trace away from nearby traces with minimum 2x distance.
4. Do not route any parallel traces above or underneath the SDIO_CLK/SPI_CLK trace.
5. Keep SDIO/SPI traces away from all clock lines and noisy power supply components such as the switcher inductors.
Avoid crossing over power supplies or ground discontinuities. SDIO/SPI traces must have a solid ground on the
layer adjacent to them.
6. Do not leave any stubs on the SDIO/SPI traces.
The image below shows the SDIO/SPI traces routing in Layer 1, as an example. The series resistor on SDIO_CLK/SPI_CLK
is placed closer to the source of this clock, rather than placing closer to the CC1 module.
Figure 4: SDIO/SPI Signals Routing in Layer 1
SDIO_D3
SDIO_D0/SPI_MOSI
SDIO_D2/SPI_INTR
SDIO_CLK/SPI_CLK
SDIO_D1/SPI_MISO
SDIO_CMD/SPI_CSN
33E Resistor

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Since SDIO_CMD/SPI_CSN, SDIO_D1/SPI_MISO, SDIO_D3 signals are present on the inner row pins of the module, these
must be routed in Layer 4 as shown below.
Figure 5: SDIO/SPI Signals Routing in Layer 4
SDIO_D3
SDIO_D1/
SPI_MISO
SDIO_CMD/
SPI_CSN

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5 USB Layout Guidelines
USB signals can reach speeds of 480 Mbps. Guidelines for the differential signals USB_DP and USB_DM must be followed.
1. It is highly recommended that the two USB differential signals (USB_DP and USB_DN) be routed in parallel with a
spacing (i.e., a) that achieves 90 Ω of differential impedances and 45 Ω for each trace.
2. To minimize crosstalk between the two USB differential signals (USB_DP and USB_DN) and other signal traces
routed close to them, it is recommended that a minimum spacing of 3xa be maintained for low-speed non-periodic
signals and a minimum spacing of 7xa be maintained for high-speed periodic signals.
3. It is recommended that the total trace length of the signals between RS9116 part and USB connector (or USB host
part) be less than 450 mm.
4. If the USB high-speed signals are routed on the Top layer, best results will be achieved if Layer 2 is a continuous
GND plane. Furthermore, there must be only one ground plane under high-speed signals and avoid the high-speed
signals crossing from GND plane to another GND plane.
5. Do not route the USB differential lines close to edge of the board.
The image below shows USB differential traces routing in Layer 1, as an example.
Figure 6: USB Signals Routing in Layer 1
USB_DP
USB_DM

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6 UART Layout Guidelines
The guidelines below must be followed for UART signals. The signals are UART1_TX, UART1_RX, UART1_RTS,
UART1_CTS.
1. Keep the UART signals away from noisy sources or other sensitive signals.
2. UART signals can be routed with multiple vias. However, ensure return path is closer to the signals.
The image below shows UART traces routing in Layer 1, as an example.
Figure 7: UART Signals Routing in Layer 1
All the UART pins are located inside. So, traces for these signals can be routed in Layer4 as shown below.
Figure 8: UART Signals Routing in Layer 4
UART1_TX
UART1_RTS
UART1_RX
UART1_CTS
UART1_RX
UART1_RTS
S
UART1_TX
UART1_CTS
S