Silicon Labs AN933.2, EFR32 User Manual

AN933.2: EFR32 Series 2 Minimal BOM

The purpose of this application note is to illustrate bill-of-material
(BOM)

and cost-optimized solutions for 2.4 GHz applications us-

ing the EFR32xG22 Wireless Gecko SoCs.

Silicon Labs reference radio board designs typically use an extensive number of com­ponents and multiple layers for RF and VDD filtering to achieve the best possible RF
performance at even the highest output power levels. So, the number of PCB layers
can be decreased and many of these elements can be eliminated from the design while
still maintaining an acceptable RF performance, especially at the lower power levels.
This document shows an absolute cost-optimized solution for the EFR32 Series 2 devi­ces targeting high-volume and cost-sensitive applications, mainly applicable for Blue­tooth Smart applications (i.e., BLE) at the 2.4 GHz frequency band, where the maxi­mum allowed fundamental RF power is generally lower and the design is typically
space-constrained, such as for wearable applications. This application note includes
measured data with several different and simplified VDD filtering approaches at the 2.4
GHz frequency region. The RF front-end matching principles are described in more de­tail in the application note, AN930.2: EFR32 Series 2 2.4GHz Matching Guide. The RF
performance also strongly depends on the PCB layout as well as the design of the
matching networks. For optimal performance, Silicon Labs also recommends using the
PCB layout design guidelines described in the application note, AN928.2: EFR32 Ser-

ies 2 Layout Design Guide.

KEY POINTS

• BOM, cost, and PCB space-optimized
reference design for 2.4 GHz applications

•

Eliminates a number of components for
RF and VDD domains while maintaining

acceptable RF performance

• Measurement results for RX sensitivity, TX
performance, and harmonics are provided

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1. Device Compatibility

This application note applies to the following EFR32 Series 2 devices:

•

EFR32BG22

• EFR32FG22

• EFR32MG22

AN933.2: EFR32 Series 2 Minimal BOM

Device Compatibility

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AN933.2: EFR32 Series 2 Minimal BOM

Design Considerations

2. Design Considerations

This section summarizes the requirements and considerations for the BOM-optimized designs for EFR32xG22 devices.

• For

minimizing costs at the manufacturing level for EFR32xG22 devices, Silicon Labs designed a 2-layer reference design board for
customers to use as reference during their design phase. So, as an ultimate low cost solution, the minimal BOM solution presented
in this application note is also applicable to the 2-layer EFR32xG22 reference design. For the schematic, layout, BOM and other
design files of the low cost reference design, see the design package.

• EFR32 internal dc-dc converter is used for supplying the following VDD rails: DVDD, PAVDD, and RFVDD.

• The on-chip dc-dc converter needs an external inductor and capacitor for proper operation. The inductor used in the 2-layer refer­ence design is CIG10W2R2MNC from Samsung, which is inexpensive and small, but can only be used for low load current. See
section 5. Recommendations for the DC-DC Converter’s External Inductor for other inductor options.

• For EFR32xG22, it is recommended to supply PAVDD, RFVDD, and DVDD from the on-chip dc-dc converter to achieve better cur­rent consumption (i.e., better power efficiency) and immunity against the battery voltage level drop and to avoid output power or RF
range degradation due to battery aging.

• For BLE 2.4 GHz applications, EFR32 needs to meet the BT Sleep Clock accuracy specification of ±500 ppm. EFR32xG22 has an
internal RC oscillator 32 kHz (LFRCO) with precision mode that meets the BLE requirements so an external low frequency crsytal
can be eliminated unless the application requires a higher clock accuracy. See section 4. Crystal Requirements if LFXO needs to be
used in the design.

• The high frequency XTAL is required for operation of RF and MCU parts of the EFR32. Load capacitors are not needed. See section

4. Crystal Requirements for the XTAL requirements.

• The RF front-end matching consists of a 3-element discrete LC structure that is needed to filter the harmonics and a dc blocking
capacitor.

• The following power supply restrictions need to be followed on the EFR32 Series 2 devices:

• VREGVDD ≥ DVDD

• DVDD ≥ DECOUPLE

• PAVDD ≥ RFVDD

• AVDD and IOVDD: No dependency with each other or any other supply pin

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AN933.2: EFR32 Series 2 Minimal BOM

Recommended BOM-optimized 2.4 GHz Solution

3. Recommended BOM-optimized 2.4 GHz Solution

The recommended RF schematic for minimal BOM option for designs using EFR32xG22 wireless MCUs is shown in the figure below:

Figure 3.1. Minimal BOM 2.4 GHz Schematic for EFR32xG22

Note: C5 (120 pF) on PAVDD can be removed as well in designs using only the 0 dBm PA.

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