Silicon Labs AN0002.1 User manual

AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

This application note details hardware design considerations for EFM32

and EFR32 Wireless Gecko Series 1 devices. For hardware design considerations for EFM32 and EZR32 Wireless MCU Series 0 devices, refer to application note AN0002.0:

EFM32 and EZR32 Wireless MCU Series 0 Hardware Design Considerations.

Topics specifically covered are supported power supply configurations, supply filtering considerations, debug interface connections, and external clock sources.

For more information on hardware design and layout considerations for the DC-DC converter on EFM32 and EFR32 Wireless Gecko Series 1 devices, see application note AN0948: EFM32 and EFR32 Series 1 Power Configurations and DC-DC.

For more information on hardware layout considerations for the radio portion of EFR32 Wireless Gecko Series 1 devices, see application notes AN930.1: EFR32 Series 1 2.4

GHz Matching Guide, AN933.1: EFR32 Series 1 Minimal BOM, and AN928.1: EFR32 Series 1 Layout Design Guide.

KEY POINTS

• Decoupling capacitors are crucial to ensuring the integrity of the device's power supplies.

•

The debug interface consists of two communication pins (SWCLK and SWDIO).

• External clock sources must be connected to the device correctly for proper operation.

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AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

1. Device Compatibility

This application note supports multiple device families, and some functionality is different depending on the device.

Device Compatibility

EFM32 Series 1

• EFM32 Jade Gecko (EFM32JG1/EFM32JG12)

• EFM32 Pearl Gecko (EFM32PG1/EFM32PG12)

• EFM32 Giant Gecko (EFM32GG11/EFM32GG12)

• EFM32 Tiny Gecko (EFM32TG11)

EFR32 Wireless Gecko Series 1 consists of:

• EFR32 Blue Gecko (EFR32BG1/EFR32BG12/EFR32BG13/EFR32BG14)

• EFR32 Flex Gecko (EFR32FG1/EFR32FG12/EFR32FG13/EFR32FG14)

• EFR32 Mighty Gecko (EFR32MG1/EFR32MG12/EFR32MG13/EFR32MG14)

consists of:

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AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

2. Power Supply Overview

2.1 Introduction

Although the EFM32 and EFR32 Wireless Gecko Series 1 devices have very low average current consumption, proper decoupling is crucial. As for all digital circuits, current is drawn in short pulses corresponding to the clock edges. Particularly when several I/O lines are switching simultaneously, transient current pulses on the power supply can be in the order of several hundred mA for a few nanoseconds, even though the average current consumption is quite small.

These kinds of transient currents cannot be properly delivered over high impedance power supply lines without introducing considerable noise in the supply voltage. To reduce this noise, decoupling capacitors are employed to supplement the current during these short transients.

2.2 Decoupling Capacitors

Decoupling capacitors make the current loop between supply, MCU, and ground as short as possible for high frequency transients. Therefore, all decoupling capacitors should be placed as close as possible to each of their respective power supply pins, ground pins, and PCB (Printed Circuit Board) ground planes.

All external decoupling capacitors should have a temperature range reflecting the environment in which the application will be used. For example, a suitable choice might be X5R ceramic capacitors with a change in capacitance of ±15% over the temperature range -55 to +85 °C (standard temperature range devices) or -55 to +125 °C (extended temperature range devices).

For regulator output capacitors (DECOUPLE, VREGSW, and VREGO, if available), the system designer should pay particular attention to the characteristics of the capacitor over temperature and bias voltage. Some capacitors (particularly those in smaller packages or using cheaper dielectrics) can experience a dramatic reduction in capacitance value across temperature or as the DC bias voltage increases. Any change pushing the regulator output capacitance outside the data sheet specified limits may result in output instability on that supply.

2.3 Power Supply Requirements

An important consideration for all devices is the voltage requirements and dependencies between the power supply pins. The system designer needs to ensure that these power supply requirements are met, regardless of power configuration or topology. Please see the device data sheet for absolute maximum rating and additional details regarding relative system voltage constraints.

EFM32 Series 1 Power Supply Requirements

• VREGVDD = AVDD (Must be the highest voltage in the system)

• VREGVDD ≥ DVDD

• VREGVDD ≥ IOVDD

• DVDD ≥ DECOUPLE

EFR32 Wireless Gecko Series 1 Power Supply Requirements

• VREGVDD = AVDD (Must be the highest voltage in the system)

• VREGVDD ≥ DVDD

• VREGVDD ≥ PAVDD (For 2.4 GHz or dual-band devices, PAVDD refers to the device pin; for sub-GHz devices, PAVDD refers to the external power amplifier supply)

• VREGVDD ≥ RFVDD

• VREGVDD ≥ IOVDD

• DVDD ≥ DECOUPLE

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AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

Power Supply Pin Overview

Note that not all supply pins exist on all devices. The table below provides an overview of the available power supply pins.

Table 2.1. Power Supply Pin Overview

Pin Name Product Family Description

AVDD All devices Supply to analog peripherals

DECOUPLE All devices Output of the internal digital LDO

IOVDD All devices GPIO supply voltage

VBUS All USB-enabled devices Primary input to the internal 3.3 V LDO, and the USB 5 V sense

input. Can be connected to the USB 5 V supply. If unused, may be left floating (a weak internal pull-down will ensure the pin remains at ground).

VREGI All USB-enabled devices Secondary input to the internal 3.3 V LDO. Typically connected

to the USB 5 V supply. If usused, may be left floating (a weak internal pull-down will ensure the pin remains at ground).

VREGO All USB-enabled devices Output of the internal 3.3 V LDO

VREGVDD All devices Input to the DC-DC converter

VREGSW All devices DC-DC powertrain switching node

VREGVSS All devices DC-DC ground

DVDD All devices DC-DC feedback node and input to the internal digital LDO

RFVDD EFR32 Wireless Gecko Series 1 only Supply to radio analog and HFXO

PAVDD EFR32 Wireless Gecko Series 1 only Supply to 2.4 GHz radio power amplifier

2.4 DECOUPLE

All

EFM32 and EFR32 Wireless Gecko Series 1 devices include an internal linear regulator that powers the core and digital logic. The

DECOUPLE pin is the the output of the digital LDO, and requires a 1 µF capacitor.

EFM32xG1 and EFR32xG1 DECOUPLE Pin

On EFM32xG1 and EFR32xG1 devices, the input supply to the digital LDO is the DVDD pin, and the DECOUPLE pin is the output of the LDO.

Main

Supply

–

DVDD1

0.1 µF

DVDD

Digital

LDO

DECOUPLE

1 µF

Digital

Logic

Figure 2.1. DVDD and DECOUPLE on EFM32xG1 and EFR32xG1 devices

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EFM32xG11/12 and EFR32xG12/13/14 DECOUPLE Pin

AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

On EFM32xG11/12 DVDD pin. The DECOUPLE pin the output of the LDO. Note that while supplied from the AVDD pin, the digital LDO current is limited to 20 mA. After start up, firmware should configure EMU_PWRCTRL_REGPWRSEL to power the digital LDO from DVDD.

2.5 IOVDD

IOVDD pin(s) provide decoupling for all of the GPIO pins on the device. A 0.1 µF capacitor per IOVDD pin is recommend, along

The with a 10 µF bulk capacitor. The bulk capacitor value may safely be reduced if there are other large bulk capacitors on the same supply (e.g., if IOVDD = AVDD = system main supply, and the main supply already has multiple 10 µF).

and EFR32xG12/13/14 devices, the input supply to the digital LDO is either the AVDD pin (power on default) or the

AVDD

Main

Supply

Figure 2.2. DVDD and DECOUPLE on EFM32xG11/12 and EFR32xG12/13/14 devices

+ –

0.1 µF

DVDD1

1 µF

DVDD

REGPWRSEL

DECOUPLE

Digital

LDO

Digital

Logic

Main

Supply

–

VDD_n

0.1 µF

IOVDD_n

. . .

IOVDD_0

IOVDD

10 µF

Figure 2.3. IOVDD Decoupling

Note: IOVDD

DC converter defaults to an unconfigured safe state with its output floating such that connected circuits remain unpowered until firmware performs the necessary configuration. Fresh from the factory, a blank device will run the bootloader and fail in its attempt to communicate with a host via the BOOT_RX and BOOT_TX pins without IOVDD power. Use of the debug interface (DBG_SWCLKTCK and DBG_SWDIOTMS) for initial firmware download would, in this case, be similarly fruitless.

should not be supplied from the DC-DC converter on EFM32xG11/12 and EFR32xG12/13/14 devices. At reset, the DC-

VDD_0

0.1 µF

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AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

2.6 AVDD

analog peripheral performance of the device is impacted by the quality of the AVDD power supply. For applications with less de-

The manding analog performance, a simpler decoupling scheme for AVDD may be acceptable. For applications requiring the highest quality analog performance, more robust decoupling and filtering is required.

Note that the number of AVDD analog power pins may vary by device and package.

2.6.1 AVDD Standard Decoupling

The figure below illustrates a standard approach for decoupling the AVDD pin(s). In general, one 10 µF bulk capacitor (C as one 10 nF capacitor for each AVDD pin (C

Main

Supply

AVDD_0

through C

+ –

), must be provided.

AVDD_n

10 nF

VDD_n

AVDD_n

. . .

AVDD

AVDD_0

VDD

10 µF

Figure 2.4. AVDD Standard Decoupling

2.6.2 AVDD Improved Decoupling

figure below illustrates an improved approach for decoupling and filtering the AVDD pin(s). In general, one 10 µF bulk capacitor

The (C

), as well as one 10 nF capacitor for each AVDD pin (C

AVDD

and series 1 Ω resistor provide additional power supply filtering and isolation.

AVDD_0

VDD_0

10 nF

through C

), must be provided. In addition, a ferrite bead

AVDD_n

), as well

Main

Supply

+ –

VDD

AVDD

1 Ω

VDD_n

10 nF

AVDD_n

. . .

AVDD_0

VDD

10 µF

Figure 2.5. AVDD Improved Decoupling

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VDD_0

10 nF

AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

The table below lists some recommended ferrite bead part numbers suitable for AVDD filtering.

Table 2.2. Recommended Ferrite Beads

Power Supply Overview

Manufacturer Part Number Impedance I

(mA) DCR (Ω) Operating Tem-

MAX

Package

perature (°C)

Würth Electronics 74279266 1 kΩ @ 100 MHz 200 0.600 -55 to +125 0603/1608

Murata BLM21BD102SN1D 1 kΩ @ 100 MHz 200 0.400 -55 to +125 0805/2012

2.7 USB (VREGI & VREGO)

Some

EFM32 and EFR32 Wireless Gecko Series 1 devices integrate a USB controller and a 3.3 V LDO. Power supply decoupling, as

well as signalling and control signals, are discussed in Section 6. USB.

2.8 DC-DC

Some EFM32 and EFR32 Wireless Gecko Series 1 devices provide an on-chip DC-DC converter that can be used for improved power efficiency. However, the additional switching noise present on the DC-DC converter output (V

), necessitates the use of specific

DCDC

filtering components.

2.8.1 DC-DC — Unused

When the DC-DC converter is not used, the DVDD pin should be shorted to the VREGVDD pin. VREGSW must be left floating, and VREGVSS should be grounded.

Bypass

witch

OFF

Main

Supply

+ –

VDD

10 µF

VDD1

0.1 µF

VREGVDD

VREGSW

DC-DC Driver

VREGVSS

DC-DC

DVDD

VDD

0.1 µF

Figure 2.6. Configuration when the DC-DC converter is unused

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AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

2.8.2 DC-DC — Powering DVDD

the lowest power applications, the DC-DC converter can be used to power the DVDD supply (as well as RFVDD and PAVDD on

For EFR32 Wireless Gecko Series 1) as shown in the figure below. In this configuration, the DC-DC Output (V

In addition to being the DC-DC converter feedback path, the DVDD pin powers the internal digital LDO, which in turn powers the digital circuits.

) is connected to DVDD.

DCDC

The system designer should pay particular attention to the characteristics of the DC-DC output capacitor (C

) over temperature and

DCDC

bias voltage. Some capacitors, particularly those in smaller packages or using cheaper dielectrics, can experience a dramatic reduction in nominal capacitance in response to temperature changes or as the DC bias voltage increases. Any change pushing the DC-DC output capacitance outside the data sheet specified limits may result in output instability on that supply.

Main

Supply

+ –

DCDC

10 µF

VDD

DCDC

4.7 µH

DCDC

4.7 µF

VDD1

0.1 µF

VREGVDD

VREGSW

VREGVSS

DC-DC Driver

Bypass

witch

OFF

DC-DC

DVDD

0.1 µF

Figure 2.7. DC-DC Converter Powering DVDD

Note: C

mended for new designs due to its improved performance under dynamic load conditions and during mode changes. Silicon Labs EFR32xG1 reference radio boards still use 1.0 µF; therefore, the EFR32xG1 software defaults to using 1.0 µF (use of emuDcdcLnCompCtrl_1u0F rather than emuDcdcLnCompCtrl_4u7F). Use of 4.7 µF on EFR32xG1 requires modification of the Low Noise Mode Compensator Control emuDcdcLnCompCtrl value. For EFR32xG12 and later, both the radio reference board hardware and the software default to 4.7 µF.

DCDC

was

1.0 µF in some previous revisions of this application note. Although 1.0 µF may still be used, 4.7 µF is now recom-

2.9 Radio (RFVDD & PAVDD) — EFR32 Wireless Gecko Series 1

On EFR32 Wireless Gecko Series 1 devices, the radio power supplies (PAVDD and RFVDD) are typically powered from one of two sources:

1. The integrated DC-DC converter. This option provides improved power efficiency but is limited to 13 dBm maximum transmit power. Additional switching noise present on the DC-DC converter output (V

), necessitates the use of specific filtering compo-

DCDC

nents.

2. The main supply. This option is less efficient but permits simpler filtering and supports systems that require transmit power in excess of 13 dBm.

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2.9.1 RFVDD and PAVDD — Powered from DC-DC

AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

RFVDD and PAVDD can be supplied from the DC-DC converter output (V

Both when V

supplies PAVDD the maximum transmit power is limited to 13 dBm. If higher power is required, PAVDD must be powered

DCDC

) for lowest power operation. Note, however, that

DCDC

from the main supply instead of the DC-DC output.

DCDC

AVDD

22 nH

RFVDD

220 nF

AVDD

10 pF

RFVDD

AVDD1

RFVDD

PAVDD

Analog

Power

Amplifier

220 nF 10 pF

Figure 2.8. RFVDD and PAVDD Decoupling (2.4 GHz application, both supplies powered from DC-DC output)

The minimal BOM option eliminates C more complete details on the minimal BOM option, along with performance comparisons, refer to AN933.1: EFR32 Series 1 Minimal

BOM.

Table 2.3. RFVDD & PAVDD Decoupling Values, Powered from DC-DC Converter

RFVDD1

and

PAVDD1

, which may allow acceptable RF performance at lower power levels. For

Application C

RFVDD

RFVDD1

PAVDD

PAVDD1

2.4 GHz 220 nF 10 pF 22 nH 220 nF 10 pF

2.4 GHz (minimal BOM) 220 nF - 22 nH 220 nF -

sub-GHz 220 nF 56 - 270 pF 100 - 270 nH 220 nF 56 - 270 pF

sub-GHz (minimal BOM) 220 nF - 100 - 270 nH 220 nF -

Table 2.4. Recommended L

Manufacturer Part Number Inductance (nH) I

MAX

22 nH Inductor

PAVDD

(mA) DCR (Ω) Operating Tempera-

Package

ture (°C)

Murata LQG15HS22NJ02D 22 ± 5% 300 0.420 -55 to +125 0402/1005

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AN0002.1: EFM32 and EFR32 Wireless Gecko Series 1 Hardware Design Considerations

Power Supply Overview

2.9.2 RFVDD and PAVDD — Powered from Main Supply

greater than 13 dBm transmit power is required, PAVDD should be powered directly from the main supply, and RFVDD may be

When powered from either the main supply or the DC-DC output (V

shown on the PAVDD input, because the main supply is presumed to be less noisy than V

Main

Supply

+ –

RFVDD

220 nF

). Note that in this configuration, the L

DCDC

RFVDD

Analog

10 pF

filter inductor is not

PAVDD

AVDD

AVDD1

Power

Amplifier

220 nF 10 pF

Figure 2.9. RFVDD and PAVDD Decoupling (2.4 GHz application, both supplies powered from main supply)

The minimal BOM option eliminates C more complete details on the minimal BOM option, along with performance comparisons, refer to AN933.1: EFR32 Series 1 Minimal

BOM.

Table 2.5. RFVDD & PAVDD Decoupling Values, Powered from Main Supply

Application C

RFVDD

2.4 GHz 220 nF 10 pF — 220 nF 10 pF

2.4 GHz (minimal BOM) 220 nF — — 220 nF —

sub-GHz 220 nF 56 - 270 pF — 220 nF 56 - 270 pF

sub-GHz (minimal BOM) 220 nF — — 220 nF —

RFVDD1

and

PAVDD1

RFVDD1

, which may allow acceptable RF performance at lower power levels. For

PAVDD

PAVDD1

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+ 23 hidden pages

Silicon Labs AN0002.1 User manual

Specifications and Main Features

Frequently Asked Questions

User Manual

1. Device Compatibility

2. Power Supply Overview

2.1 Introduction

2.2 Decoupling Capacitors

2.3 Power Supply Requirements

2.4 DECOUPLE

2.5 IOVDD

2.6 AVDD

2.6.1 AVDD Standard Decoupling

2.6.2 AVDD Improved Decoupling

2.7 USB (VREGI & VREGO)

2.8 DC-DC

2.8.1 DC-DC — Unused

2.8.2 DC-DC — Powering DVDD

2.9 Radio (RFVDD & PAVDD) — EFR32 Wireless Gecko Series 1

2.9.1 RFVDD and PAVDD — Powered from DC-DC

2.9.2 RFVDD and PAVDD — Powered from Main Supply