Silicon Laboratories EFM32 Series Hardware Design Manuallines
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Silicon Laboratories EFM32 Series Hardware Design Manuallines

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AN0046: USB Hardware Design Guidelines
This application note gives recommendations on hardware design for implementing USB
host and device applications using USB capable EFM32 microcontrollers along with
some example schematics for different applications.
silabs.com | Building a more connected world.
KEY POINTS
• Example Schematics for a variety of
applications
• PCB Design Guidelines for new
applications
Rev. 1.02

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Summary of Contents for Silicon Laboratories EFM32 Series

  • Page 1 AN0046: USB Hardware Design Guidelines This application note gives recommendations on hardware design for implementing USB host and device applications using USB capable EFM32 microcontrollers along with KEY POINTS some example schematics for different applications. • Example Schematics for a variety of applications •...
  • Page 2 AN0046: USB Hardware Design Guidelines Introduction 1. Introduction Some EFM32 microcontrollers, for instance selected members of the Giant Gecko and Leopard Gecko families, offer on-chip USB sup- port. The USB peripheral embedded on these devices include the USB PHY and an internal voltage regulator, thus requiring only a minimum number of external components.

  • Page 3: Usb Connection

    AN0046: USB Hardware Design Guidelines USB Connection 2. USB Connection This section gives a brief overview of the different USB roles an EFM32 Microcontroller is capable of. For more in-depth details, please refer to the device family reference manual. USB can be operated in 2 different modes; host or device, with hub being a special version of a USB device. A supplement to the USB standard introduces "On-The-Go"...
  • Page 4 AN0046: USB Hardware Design Guidelines USB Connection 2.2 EFM32 as USB Host In host mode, the EFM32 acts as the bus master and is responsible of enumerating the USB devices, a process that includes inquiring connecting devices for configuration information and assigning them an address on the USB bus. The USB host also controls data flow on the bus by sequentially polling all devices for data, meaning that no device can transmit on the bus without a host request.
  • Page 5 AN0046: USB Hardware Design Guidelines USB Connection 2.3.1 Self Powered Device 1.85 – 3.6 V USB_VREGO 1 µF USB_VREGI 4.7 µF USB Series B, USB_VBUSEN EFM32 USB Series Mini-B or USB Series Micro-B receptacle USB_VBUS VBUS USB_DP 15 R USB_DM 15 R USB_DMPU Connector...
  • Page 6 AN0046: USB Hardware Design Guidelines USB Connection 2.3.2 Bus Powered Device USB_VREGO 1 µF USB_VREGI 4.7 µF USB Series B, USB_VBUSEN EFM32 USB Series Mini-B or USB Series Micro-B receptacle USB_VBUS VBUS USB_DP 15 R USB_DM 15 R USB_DMPU Connector shield USB_ID Figure 2.3.
  • Page 7 AN0046: USB Hardware Design Guidelines USB Connection 2.3.3 Low-speed Speed identification of USB devices is done with a pull-up on one of the data lines. A low-speed capable device is identified by a 1.5 kohm pull-up resistor on the D- line. The internal pull-up resistor on EFM32 microcontrollers is approximately 2.2 kohm, so an external 4.7 kohm resistor must be placed in parallel to be standard compliant.
  • Page 8 AN0046: USB Hardware Design Guidelines USB Connection 2.4 EFM32 as USB On-The-Go Dual Role Device On-The-Go Dual Role Device (OTG) is not yet supported in the EFM32 USB stack, but EFM32 hardware is OTG capable. When operating as a OTG Dual Role Device, a USB product is capable of operating both as a USB host and a USB device. A dual role capable device must use a Micro-AB receptacle which can accept both a Micro-A plug and a Micro-B plug.

  • Page 9: Pcb Design Guidelines

    AN0046: USB Hardware Design Guidelines PCB Design Guidelines 3. PCB Design Guidelines This section presents some basic guidelines for high-speed PCB design as well as some specific rules of thumb for USB full-speed design. 3.1 Recommended Routing Rules of Thumb •...
  • Page 10 AN0046: USB Hardware Design Guidelines PCB Design Guidelines 3.3.1 Differential Pairs The USB data lines, D- and D+, should be routed as a differential pair. The trace impedance should be matched to the USB cable differential impedance, which is nominally 90 ohms for the signal pair. The impedance of a signal track is mainly determined by its geometry (i.e.
  • Page 11 AN0046: USB Hardware Design Guidelines PCB Design Guidelines 3.3.2 Reference Planes Routing high speed signals across a split in the reference plane should be avoided. In high speed digital design, one always have to consider the complete current loop from a transmitter output and back to the transmitter reference terminal, including the return current in ground or another reference plane.
  • Page 12 AN0046: USB Hardware Design Guidelines USB Electrical Specifications 4. USB Electrical Specifications The EFM32 USB peripheral are USB 2.0 compliant and can operate as a USB host, USB device and as an On-The-Go dual-role de- vice. The USB 2.0 standard specifies three data rates: •...
  • Page 13 AN0046: USB Hardware Design Guidelines USB Electrical Specifications 4.2.2 Low-speed Low speed: Rise/fall time (10-90%) 75-300 ns. 4.3 Speed Identification A USB device must identify its data rate capabilites to the USB host. To do this, the USB standard has set up a scheme where USB hosts have a weak pull-down resistor on both data lines, and devices have a strong pull-up resistor on one of the data lines.
  • Page 14 AN0046: USB Hardware Design Guidelines USB Electrical Specifications 4.4.1 USB Receptacles Figure 4.3. USB Series A Receptacle for USB Host Figure 4.4. USB Series B Receptacle for USB Device Figure 4.5. USB Series Mini-B Receptacle for USB Device. Smaller form factor. Figure 4.6.
  • Page 15 AN0046: USB Hardware Design Guidelines Power 5. Power 5.1 USB Voltage Regulator The EFM32 feature an on-chip 5 V to 3.3 V regulator that is used to power the internal USB PHY. This ensures that the USB signaling levels remain constant and within specification regardless of the voltage level on the rest of the device. But as the regulator can output up to 50 mA, it can also be used to power both the rest of the EFM32 as well as external components.

  • Page 16: Environmental Considerations

    AN0046: USB Hardware Design Guidelines Environmental Considerations 6. Environmental Considerations In this section these phenomena are discussed: • EMI (Electromagnetic Interference); electromagnetic noise generated by an apparatus • EMC (Electromagnetic Compatibility); an apparatus' immunity against electromagnetic noise • ESD (Electrostatic Discharge); an apparatus' immunity against electrostatic discharges 6.1 Isolation of Cable Shield Any cable will act as an antenna that can radiate as well as and pick up electromagnetic noise.
  • Page 17 AN0046: USB Hardware Design Guidelines Environmental Considerations 6.2 ESD Protection The USB pins on EFM32 devices are tolerant of a 2 kV discharge according to the Human Body Model (HBM). Designers should be aware that the HBM model is only intended to model ESD events that may happen in a production environment. I.e. a device that is designed to withstand a HBM discharge will survive being handled during production.
  • Page 18 AN0046: USB Hardware Design Guidelines Environmental Considerations Figure 6.2. Recommended ESD Protection The EFM32GG-STK3700 Giant Gecko Starter Kit has been tested according to IEC 61000-4-2 and has passed an 8 kV contact dis- charge. The ESD protection cirquitry should be placed near the USB connector to prevent the high voltages and frequencies of an ESD event to propagate far into the PCB.

  • Page 19: Further Reading

    AN0046: USB Hardware Design Guidelines Further Reading 7. Further Reading Universal Serial Bus Specification (Revision 2.0) including USB On-The-Go and Embedded Host Supplement to the USB Revision 2.0 Specification. • https://www.usb.org/sites/default/files/documents/usb_otg_and_eh_3-0_release_1_1_10may2012.pdf Human Body Model vs. IEC 61000-4-2 (Protek Devices) • http://www.protekdevices.com/xyz/documents/kb/tech/ta1036.pdf High Speed USB Platform Design Guidelines (Intel) •...

  • Page 20: Revision History

    AN0046: USB Hardware Design Guidelines Revision History 8. Revision History Revision 1.02 June 2020 • Revised example schematics to remove unnecessary ferrite beads • Updated document links Revision 1.01 September 2013 • New Cover Layout Revision 1.00 January 2013 • Initial Revision. silabs.com | Building a more connected world.
  • Page 21 Trademark Information Silicon Laboratories Inc.®, Silicon Laboratories®, Silicon Labs®, SiLabs® and the Silicon Labs logo®, Bluegiga®, Bluegiga Logo®, ClockBuilder®, CMEMS®, DSPLL®, EFM®, EFM32®, EFR, Ember®, Energy Micro, Energy Micro logo and combinations thereof, "the world’s most energy friendly microcontrollers", Ember®, EZLink®, EZRadio®, EZRadioPRO®, Gecko®, Gecko OS, Gecko OS Studio, ISOmodem®, Precision32®, ProSLIC®, Simplicity Studio®, SiPHY®, Telegesis, the Telegesis Logo®, USBXpress®...

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