AN64285 Wirelessusb™ NL Low Power Radio Recommended Usage and PCB Layout Associated Project: Yes Associated Part Family: CYRF8935 Software Version: NA Related Application Notes: None To get the latest version of this application note, or the associated project file, please visit http://www.cypress.com/go/AN64285. Wireless products are now found in abundance, all around us today, and their usage continues to rapidly expand. This application note introduces the Cypress CYRF8935 device and a sample PCB design. The appendix section guides you on antenna selection process. Contents Introduction Introduction ....................................................................... 1 Files List ............................................................................ 1 Understanding the Schematic ........................................... 1 DC Power ..................................................................... 1 MCU Interface .............................................................. 2 Crystal Oscillator .......................................................... 2 RF/Antenna Connection ............................................... 2 Schematic Diagram ........................................................... 3 PCB Layout Notes ............................................................. 4 Bill of Materials .................................................................. 7 Appendix A – Antenna Recommendations ........................ 8 Appendix B – PIFA Dimensions ........................................ 9 Worldwide Sales and Design Support ............................. 11 This note describes the NL RF module reference design, based on the CYRF8935 device. Various antenna choices are introduced, enabling designers to easily add 2.4 GHz wireless linking to a product. Files List The following PC files accompany this application note. File Name Contents 001-64285.pdf This file. NL_Altium.zip Altium schematic and PCB layout. NL_OrCAD.zip OrCAD schematic of module, OrCAD reference design. Antennas.zip Documents for various antennas discussed. Understanding the Schematic The schematic has four (4) basic categories of circuitry: DC Power, MCU interface, Crystal Oscillator, and RF/Antenna Connection. DC Power Refer to pins 1, 2, 5, 8, 9, 19, and 22 of the device, on the schematic. www.cypress.com Document No. 001-64285 Rev. *B 1 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout The CYRF8935 features an on-chip low dropout (LDO) regulator that is optimized for the analog mixed signal (AMS) and radio frequency (RF) needs of the device. The LDO regulator input pin, VIN, connects to input power, while the output pin, VOUT, connects to each of the VDD pins of the device, as shown in the schematic. It is recommended that VDD bypass capacitors be placed approximately at the corners of the chip. See the sample layout shown in the figures. Note that if the source of DC input power is from a switching power converter that may have high noise, additional DC filtering may be needed. Schematic note 3 details this, and provides initial guidance. Note that a separate VDD_IO pin is provided. Internal to the CYRF8935 device, this voltage drives the MCU interface I/O pads. In other words, voltage on this pin sets the expected I/O voltages. It normally connects to the same voltage source as the MCU. MCU Interface SPI: Refer to pins 13, 15, 16, and 17 of the device, on the schematic. The primary MCU interface is a conventional 4-wire SPI. IRQ: Refer to pins 10 and 14 of the device, on the schematic. The CYRF8935 can generate two IRQ signals for the MCU. Most applications will only need the PKT IRQ output. PKT is used to inform the MCU that a packet is ready to be received, or a packet has been transmitted. FIFO is an IRQ that indicates the internal FIFO is running high (for Rx), or low (for Rx), and may need imminent read or write by the MCU. In addition, the CYRF8935 expects a reset signal to initialize the device. This signal derives from a dedicated GPIO. Correct crystal loading is checked by measuring the frequency on BRCLK, pin 18. At power-up, it should measure 3.000,00 MHz; within approximately 10 ppm to 20 ppm error (It is better if the frequency error is at the least). Frequency on BRCLK is only accessible on bare die parts. For packaged parts, crystal loading is checked by measuring transmit carrier frequency; see datasheet for instructions. Under room temperature, nominal test conditions, frequency error should measure no more than 10 to 20 ppm. See datasheet for more in-depth detail regarding crystal specifications. For proper startup, it is normally the Rs specification that is most important. See datasheet for maximum Rs specification for the crystal. RF/Antenna Connection Refer to pins 3 and 4 of the device, on the schematic. The shunt capacitor and series inductor serve to improve the impedance match between device and antenna. The values shown should not be modified. When selecting these components, choose parts that have low loss at RF. The chosen parts should exhibit a minimum Q of approximately 20 or better, at 2.4 GHz. For EMC compliance testing, direct coaxial cable connection to the RF lab equipment is often helpful, as shown by the SMA connector in this reference design. Without the direct coaxial cable connection, a shielded and calibrated TEM cell test box may be necessary for some of the regulatory and EMC compliance testing. Note See http://www.temcell.com/ and http://www.rfshieldbox.com/products.html Crystal Oscillator Refer to pins 23 and 24 of the device, on the schematic. A good quality, low-cost external quartz crystal element is used as the frequency standard for the RF transceiver. For error free data transmission and reception, the oscillation must be free of excess phase noise and jitter. Circuit operation is explained in the CYRF8935 datasheet. Appropriate crystal loading capacitors must also be supplied as detailed in the datasheet. www.cypress.com Document No. 001-64285 Rev. *B 2 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Schematic Diagram Figure 1. Schematic Diagram for the PCB www.cypress.com Document No. 001-64285 Rev. *B 3 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout PCB Layout Notes Following are the general guidelines to be observed as a matter of good design practice. Highly important items are underlined, and their application is illustrated on the layout figures. RF layout guidelines Use ground vias liberally Keep RF traces short for low-loss Crystal layout guidelines Solid RF ground plane between RFIC and Antenna. Minimal ground noise on the crystal load capacitors Ground via for each capacitor Ground the crystal case if possible Keep some separation between XTALi and XTALo. Grounds fill between the crystal leads. Miscellaneous layout guidelines Ground vias under or at critical components a. RFIC b. Crystal c. Decoupling capacitors d. RF transmission line Figure 2. Top view of PWB. Top layer of PWB (red) www.cypress.com Document No. 001-64285 Rev. *B 4 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Figure 3. Top view of PWB, looking through the top layer to view the bottom layer of PWB (blue) Overall dimensions: 1250 x 850 Mils www.cypress.com Document No. 001-64285 Rev. *B 5 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Figure 4. Completed PCB Assembly Current measurement Test Points To use, cut the 8-mil jumper trace between the through-holes; install JP1 header pins. Connect to ammeter. Header mounted on back side. SMA RF connector Fiducials for automated assembly (3 each). FIFO and extra ground pin not normally needed. www.cypress.com Document No. 001-64285 Rev. *B 6 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Bill of Materials Qty ==== 1 2 4 Part Type Designator Footprint ========================== ========== ================== 1.0pF C3 0603 15pF C7 C8 0603 0.10uF C1 C4 C5 0603 C6 (see sch. note) 1 1 1 1 680 k 2.2 k 20 k 51 R2 R3 R4 R5 0603 0603 0603 0603 1 2.2nH L1 0603 1 1 SMA-Female 10-pin hdr, 100-mil J1 P1 SMA_LAUNCH HDR2X5 1 CYRF8935 U1 QFN24 1 Quartz xtal 12 MHz Y1 XTL_49SS C9 R1 JP1 P2 Y2 0603 HDR1X2 XTL_4X2.5 Not used: 2 Note 1 2 Note 1 1 Note 1 Note 1 Do not install parts labeled “Note 1”. www.cypress.com Document No. 001-64285 Rev. *B 7 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Appendix A – Antenna Recommendations The antenna is normally the biggest factor in achieving successful performance. A rigorous antenna tutorial is beyond the scope of this paper, but some simple antenna recommendations that can be easily applied to CYRF8935 applications are introduced. Virtually any type of good-quality 50 ohms, 2.4 GHz antenna can be used with the CYRF8935. Several choices are shown in Table 1. Table 1. Antenna Choices Antenna type Picture or Drawing Wiggle antenna DC Grounded? See sch. Note 2 Yes Description/Notes Described in Cypress Semiconductor AN48610 (Doc. no. 001-48610) Cost: Almost free of cost when added to existing PCB. Custom printed-trace antenna This is a specialized antenna, customized to each application. Chip antenna Depends on the design No Cost: Almost free of cost when added to existing PCB. Easy to use. Ensure to read the datasheet and follow all manufacturer instructions. Manufacturer’s specification for mounting and layout must be exactly followed. Model 2450AT18B100E, Johanson Technology Inc. Cost: Can be expensive. PIFA Yes The Printed Inverted-F Antenna (PIFA). Cost: Almost free of cost when added to existing PCB. See Appendix B – PIFA Dimensions for detailed drawing. 1/2 wave end-fed dipole No Delivers ‘textbook’ 0 dBd performance. Easy removal and replacement. Accommodates EMC compliance and end applications. Requires RF connect on the board. Cost: Relatively expensive. Illustrated: Model W1010, by Pulse. Antenna designs with inherent DC grounding are generally preferred over non-DC grounded designs. Grounded designs have inherently better ESD immunity, and the need for the 20 K resistor on CYRF8935 ANT pin is eliminated. www.cypress.com Document No. 001-64285 Rev. *B 8 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Appendix B – PIFA Dimensions For 2.4 GHz. Substrate material is 1/32 inch (0.031) FR-4. Note that ideal dimensions may vary slightly, depending on application. www.cypress.com Document No. 001-64285 Rev. *B 9 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Document History Document Title: WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout - AN64285 Document Number: 001-64285 Revision ECN Orig. of Change Submission Date Description of Change ** 3037038 HEMP 09/23/2010 New Application Note. *A 3349669 HEMP 09/13/2011 Content updated to QFN-24. *B 4542074 CSAI 10/17/2014 Updated to new template. Completing Sunset Review. www.cypress.com Document No. 001-64285 Rev. *B 10 WirelessUSB™ NL Low Power Radio Recommended Usage and PCB Layout Worldwide Sales and Design Support Cypress maintains a worldwide network of offices, solution centers, manufacturer’s representatives, and distributors. To find the office closest to you, visit us at Cypress Locations. PSoC® Solutions Products Automotive cypress.com/go/automotive psoc.cypress.com/solutions Clocks & Buffers cypress.com/go/clocks PSoC 1 | PSoC 3 | PSoC 4 | PSoC 5LP Interface cypress.com/go/interface Lighting & Power Control cypress.com/go/powerpsoc cypress.com/go/plc Memory cypress.com/go/memory PSoC cypress.com/go/psoc Touch Sensing cypress.com/go/touch USB Controllers cypress.com/go/usb Wireless/RF cypress.com/go/wireless Cypress Developer Community Community | Forums | Blogs | Video | Training Technical Support cypress.com/go/support WirelessUSB™ is the trademark of Cypress Semiconductor Corporation. All other trademarks or registered trademarks referenced herein are the property of their respective owners. Cypress Semiconductor 198 Champion Court San Jose, CA 95134-1709 Phone Fax Website : 408-943-2600 : 408-943-4730 : www.cypress.com © Cypress Semiconductor Corporation, 2010-2014. The information contained herein is subject to change without notice. Cypress Semiconductor Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. This Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide patent protection (United States and foreign), United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of, and compile the Cypress Source Code and derivative works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source Code except as specified above is prohibited without the express written permission of Cypress. Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the right to make changes without further notice to the materials described herein. Cypress does not assume any liability arising out of the application or use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress’ product in a life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges. Use may be limited by and subject to the applicable Cypress software license agreement. www.cypress.com Document No. 001-64285 Rev. *B 11