CC13xx/CC26xx Hardware Configuration and PCB Design Considerations

1 Reference Design

Texas Instruments (TI) offers LaunchPad™ development platforms as the primary development environment for CC13xx and CC26xx devices. These platforms feature optimized external RF components, on-board antennas, and integrated debuggers for an easy-to-use experience. Each CC13xx/CC26xx family member is available on a dedicated LaunchPad with RF matching networks and antennas tailored for specific ISM bands. Design files for these LaunchPads are available on ti.com and can serve as a reference for custom hardware integration.

Sub-1 GHz LaunchPads:

• LAUNCHXL-CC1310: Features CC1310, operates on 868 MHz and 915 MHz ISM bands, uses a Monopole PCB Antenna with Single or Dual Band Option, and has a differential, external bias RF front end.
• LAUNCHXL-CC1312R: Features CC1312R, operates on 868 MHz and 915 MHz ISM bands, uses a Monopole PCB Antenna with Single or Dual Band Option, and has a differential, external bias RF front end.

2.4 GHz LaunchPads:

• LAUNCHXL-CC2640R2: Features CC2640R2F, operates on 2.4 GHz ISM band, uses a 2.4-GHz Inverted F Antenna, and has a differential, internal bias RF front end.
• LAUNCHXL-CC26x2R: Features CC2652R, operates on 2.4 GHz ISM band, uses a 2.4-GHz Inverted F Antenna, and has a differential, internal bias RF front end.

Dual-Band LaunchPads:

• LAUNCHXL-CC1350EU/US: Features CC1350, supports 868 MHz/915 MHz and 2.4 GHz ISM bands, uses Miniature Helical PCB Antenna for 868 MHz or 915/920 MHz and a 2.4-GHz Inverted F Antenna, with a differential, external bias RF front end. It allows switching between RF front ends and antennas for different bands.
• LAUNCHXL-CC1350-4: Features CC1350, supports 433 MHz and 2.4 GHz ISM bands, uses Miniature Helical PCB Antenna for 868 MHz or 915/920 MHz and a 2.4-GHz Inverted F Antenna, with a differential, external bias RF front end.
• LAUNCHXL-CC1352R: Features CC1352R, supports 868 MHz, 915 MHz, and 2.4 GHz ISM bands, uses a Monopole PCB Antenna with Single or Dual Band Option, and has a differential, external bias RF front end. It utilizes an RF switch or diplexer to route signals to a shared antenna.
• LAUNCHXL-CC1352P1: Features CC1352R, supports 868 MHz, 915 MHz, and 2.4 GHz ISM bands, uses a Monopole PCB Antenna with Single or Dual Band Option, and has a differential, external bias RF front end. It offers multiple RF paths with an RF switch for different bands and power levels.
• LAUNCHXL-CC1352P-2: Features CC1352P, supports 868 MHz, 915 MHz, and 2.4 GHz ISM bands, uses a Monopole PCB Antenna with Single or Dual Band Option, and has a differential, external bias RF front end. It supports multiple RF paths with an RF switch.
• LAUNCHXL-CC1352P-4: Features CC1352P, supports 433 MHz, 470 MHz, 510 MHz, and 2.4 GHz ISM bands, uses a Monopole PCB Antenna with Single or Dual Band Option, and has a differential, external bias RF front end. It includes an external component (LANT) for the 433-510 MHz band to extend antenna structure.

Reference Design Overview: When designing custom boards, following reference designs is crucial. TI provides a table (Table 1) mapping supported devices and ISM bands to specific reference designs, allowing for component reuse across different designs.

2 Front-End Configurations

CC13xx/CC26xx devices support different front-end modes:

• Single-ended: Uses either the RF_P or RF_N pin for the RF path.
• Differential: Uses both RF_P and RF_N pins for a differential RF interface.
• LNA Biasing: The Low-Noise Amplifier (LNA) can be biased using an internal or external inductor, applicable to both single-ended and differential configurations.

Figure 1 illustrates these front-end options, with red components indicating those required only for external bias. Figure 2 compares the pros and cons of External Bias vs. Internal Bias and Differential vs. Single-Ended configurations, highlighting trade-offs in footprint, BOM cost, sensitivity, and output power.

Configuring Front-End Mode: The front-end mode is set using the CMD_RADIO_SETUP command, specifying Config.frontEndMode. For single-ended operation requiring different pins for RX and TX, an additional override (ADI_HALFREG_OVERRIDES) is necessary. LNA biasing is configured via config.biasMode.

CC13xx Single-Ended Mode: For sub-1 GHz designs, differential configuration is typical for long range, but single-ended can be used for lower cost and smaller footprint at the expense of range. Specific matching networks are provided for single-ended TX-only (Figure 3) and RX-only (Figure 4) operations, detailing component values for optimal performance.

CC26xx: Single-ended configuration is recommended for CC26xx when maximum output power is not critical, offering lower current consumption and component count.

3 Schematic

The schematic section details the typical components and their connections for the RF front-end.

Schematic Overview (Figure 5): Depicts the CC1312R 7x7 RF part, showing connections for crystal oscillators (24/48 MHz and 32.768 kHz), RF pins (RF_P, RF_N, RX_TX), power supply pins (VDDS, VDDR, DCOUPL), and JTAG interface pins. It highlights the use of external crystal load capacitors.

24/48 MHz Crystal: Essential for radio operation, this crystal can cause spurs at N x 48 MHz offsets. Adjusting XOSC tuning capacitors can reduce these spurs. External load capacitors are recommended for compliance with certain regulations and for +20 dBm PA operation.

32.768 kHz Crystal: Optional, used for RTC timing. An external crystal improves sleep clock accuracy and reduces power consumption for Bluetooth Low Energy. It is required for time-synchronous protocols.

Balun: Transforms balanced (differential) to unbalanced (single-ended) signals, often implemented with low-pass and high-pass filters. Symmetry is key for optimal performance.

Filter: An LC filter between the balun and antenna attenuates harmonics and performs impedance matching to 50 Ω.

RX_TX Pin: Provides ground connection for the LNA in RX, enabling external bias for improved sensitivity.

Decoupling Capacitors (Figure 6): Placed close to supply pins to minimize noise coupling. Proper routing and via connections to ground are critical for performance.

Antenna Components: A pi-match network is recommended for impedance matching between the LC filter and the antenna.

RF Shield: Used in some TI reference designs to reduce spurious signal radiation.

I/O Pins Drive Strength: I/O pins support configurable drive strengths (2 mA, 4 mA, and up to 8 mA for specific pins).

Bootloader Pins: Used for communication with external devices via UART or SSI interfaces. Specific DIO pins are configured for these functions.

AUX Pins: Signals from the sensor controller domain (AUX Domain) can be routed to specific DIO pins, with some AUXIO signals supporting analog capability.

JTAG Pins: Used for on-chip debug support via cJTAG or JTAG interfaces, with specific pins assigned for TCK, TMS, TDI, and TDO.

4 PCB Layout

Proper PCB layout is critical for RF performance.

Board Stack-Up (Figure 7): Details the layer structure of the PCB, emphasizing the distance between the top layer and the ground layer. Deviations can affect parasitics and require filter balun re-design.

Balun (Figure 8): Requires symmetrical layout for optimal amplitude and phase balance. Asymmetrical baluns can lead to higher harmonics and reduced output power. Uninterrupted ground planes are essential.

LC Filter (Figure 9): Layout should minimize crosstalk between shunt components. TI recommends specific layout practices for best performance.

Decoupling Capacitors (Figure 10): General rules include placing them on the same layer as the active component, routing power to them first, and using separate vias to ground to minimize noise coupling. A short and direct ground return path is crucial.

Current Return Path (Figure 11): A solid ground plane is necessary for the return path of decoupling capacitor currents to the chip to prevent performance degradation and spurious emissions.

DC/DC Regulator (Figure 12): DC/DC components must be placed close to the DCDC_SW pin, with a short, direct ground connection for the output capacitor.

Antenna Matching Components: A pi-network is recommended and should be placed close to the antenna.

Transmission Lines: Traces from the LC filter to the antenna should maintain a 50 Ω impedance. TXLine is a tool for calculating PCB trace impedance.

Electromagnetic Simulation: Recommended for designs deviating from reference designs to simulate and compare performance.

5 Antenna

Antenna selection and matching are crucial for optimal performance.

Single-Band Antenna (Figure 13): A pi-match network is recommended prior to the antenna to tune and reduce mismatch losses. ANT2 is always used, while ANT1 or ANT3 depends on antenna impedance.

Dual-Band Antenna (Figure 14): For dual-band operation, an LC, CL match network is recommended over a pi-match. The LC section matches the high band, and the CL section matches the low band.

Dual-Band Antenna Match Examples:

• 863-928 MHz and 2.4 GHz (Figure 15, 16, 17, 18): Details the process of matching a dual-band antenna using specific component values (LHIGH, CLOW) and measurements (impedance, VSWR) to achieve good performance across both bands.
• 433-510 MHz and 2.4 GHz (Figure 19, 20): Describes using an external component (LANT) for the lower frequency band and provides matching procedures and VSWR results.

6 Crystal Tuning

Proper crystal oscillator configuration is vital for accurate timing and radio operation.

CC13xx/CC26xx Crystal Oscillators (Figure 21): Devices feature high-frequency (HFXOSC, 24/48 MHz) and low-frequency (LFXOSC, 32.768 kHz) crystal oscillators. HFXOSC is mandatory for radio operation, while LFXOSC is for RTC timing.

Pierce Type Oscillator (Figure 22): Both oscillators are Pierce type, requiring proper dimensioning of load capacitors based on the crystal's capacitive load (CL) parameter.

Crystal Selection: Consult device-specific data sheets for crystal parameter requirements.

Tuning the LF Crystal Oscillator: Load capacitors (C1, C2) are dimensioned relative to the crystal's load capacitance (CL). Equation 2 provides the formula for calculating load capacitance, considering parasitic capacitance.

Tuning the HF Oscillator: The HF oscillator uses internal variable load capacitors (cap-array). Load capacitance is set via CCFG.c defines. Table 7 provides CCFG delta values for tuning the cap-array based on measured capacitance, allowing adjustment via SmartRF™ Studio.

7 Integrated Passive Component (IPC)

IPC's are matched-filter balun components that reduce component count and assembly costs. Table 8 lists available IPCs from vendors like Johanson Technology, Walsin, Murata, and Anaren, specifying chip families, frequency ranges, part numbers, and associated application reports.

8 Optimum Load Impedance

CC13xx/CC26xx performance is highly dependent on filter-balun impedance across multiple harmonics. Matching load impedance at the fundamental frequency alone can lead to issues. Following TI's reference designs (schematic, layout, stack-up) is recommended for optimal TX/RX performance. Impedance values can vary based on device state (TX/RX) and signal level. Specific target load impedances are provided for CC26xx, CC1310/CC1312, and CC1352R/CC1352P across various frequency bands.

9 Power Supply Configuration

The devices utilize three power rails: VDDS, VDDR, and DCOUPL.

DC/DC Converter Mode (Figure 23): Maximizes efficiency by using an internal DC/DC converter, requiring external inductor and capacitor components placed close to the device. The system dynamically switches between LDO and DC/DC converter for optimal efficiency. If VDDS drops below 2.0 V, the device may operate in global LDO mode.

Global LDO Mode (Figure 24): Offers cost and PCB area savings by removing the DC/DC inductor. VDDR is supplied from the Global LDO, potentially increasing power consumption. The VDDS_DCDC pin must be connected to VDDS, and DCDC_SW left floating.

External Regulator Mode (Figure 25): Neither Global LDO nor DC/DC is active; both VDDS and VDDR are powered from the same external rail. Regulators are disabled by grounding VDDS_DCDC. This mode is supported only on CC26x0 devices.

10 Board Bring-Up

Before software development or range testing, conducted measurements are recommended to verify hardware performance, including sensitivity, output power, harmonics, and current consumption.

Power On: Verify expected voltage levels on VDDR and DCOUPL pins. Avoid direct measurement on X24M_P/N and X48M_P/N pins to prevent device damage.

RF Test: SmartRF Studio: Requires a debugger connection. Steps involve connecting a debugger, verifying device visibility, performing packet transmission/reception tests between known boards and the device under test (DUT), and comparing results. Antenna tuning is crucial for accurate measurements.

RF Test: Conducted Measurements:

• Sensitivity: Measure at the SMA connector or semi-rigid coax cable. Use PacketRX in SmartRF Studio. A signal generator is preferred for transmitting packets; otherwise, an EM/LaunchPad can be used. Accurate measurements may require a shielded box.
• Output Power: Measure at the SMA connector using a spectrum analyzer (SA) with a 1 MHz RBW.

Software Bring-Up: For CC13xx and CC26xx, basic RF examples and driver examples are available on ti.com. It is recommended to run these examples unmodified first to verify functionality before proceeding with custom software development.

Hardware Troubleshooting: Covers common issues like no link (RF settings, frequency offset), poor link (antenna mismatch), Bluetooth Low Energy connection problems, DCDC layout issues affecting sensitivity, and high sleep power consumption.

11 References

This section lists various TI resources, tools, and documentation relevant to CC13xx/CC26xx hardware design, including transmission line calculators, antenna selection guides, specific LaunchPad design files, technical reference manuals, and application reports from Texas Instruments and other vendors.