This is the USB configuration for self powered mode for an EFM32 device -
Problem - If USB insertion occurs before VDD is powered up
In self-powered mode, the chip is powered from an external USB 5V supply. This means that there is the potential for the 5V to be present on the device pins when the AVDD is at 0 V. This would damage the device since the IO pins will have a voltage that exceeds VDD + 0.3 V.
The USB I/O pins (USB D+/D- etc) are tied to:
1. The typical GPIO pad drivers which are powered from IOVDD
2. Some analog drivers specific to USB which are powered from VREGO
The USB PHY is expecting the MCU to be up and running (i.e., VDD=AVDD=IOVDD are valid) before the USB PHY is powered (or at least at the same time). If USB PHY is powered up while VDD=AVDD=IOVDD is low (e.g., Self-powered case), there is a possibility the USB PHY’s analog drivers could begin driving a voltage on the USB IO pads. This would be violating the VDD+0.3V absolute maximum specification on the IO pad.
Workaround
There are a couple of workarounds available to address this issue:
1. A PFET switch could be added between the USB_VBUS pin and the USB jack VBUS 5V supply. The gate of this switch would be controlled by VDD, such that when VDD=0V the switch was open and when VDD>1.8V the switch was closed
2. Another option could be to not use the LDO in the self-powered case. For example, tying VDD=AVDD=IOVDD=USB_VREGI=USB_VREGO. In this case, it wouldn’t be possible for the USB_VREGO to exceed IOVDD.
In some of the documentation under the Soldering Information section it states, "Place as many and as small as possible vias underneath each of the solder patches under the ground pad," does this mean to put filled or covered vias?
Answer
The vias should be filled. If they are left open, the solder has the potential to wick into the holes and cause random fallout due to the part skewing on the PCB.
What is the difference between USB functionality on the EFM32 Happy Gecko, compared to other EFM32 USB devices (Wonder Gecko, Giant Gecko, and Leopard Gecko)?
Answer
Happy Gecko supports device mode only, other devices support device, host, or OTG.
Happy Gecko does not require a crystal oscillator, and can run USB with a 24MHz sysclk. Other devices require a 48MHz crystal.
Happy Gecko also supports low energy USB modes, which reduces current consumption when USB is idle. See AN0886: Happy Gecko Low Energy USB Overview for more information on these modes. Application notes can be found in Simplicity Studio or at www.silabs.com/32bit-appnotes.
What USB audio examples are available for the EFM32?
Answer
There are two USB audio examples (USB Audio Class 1.0) for the EFM32. These examples can be found using the Software Examples tile in Simplicity Studio. The two examples are:
usbdheadphone
usbdmicrophone
Both of these examples are available for the EFM32GG, EFM32LG, and EFM32WG Development Kits.
These examples can also be found on disk here by default:
When I perform a USB reset, the USB GRSTCTL register's AHBIDLE flag is never set. What is the issue?
Answer
In our examples when performing a USB core reset, we perform the USB soft reset, wait 1 µs, then poll AHBIDLE. Ensure the USB soft reset is performed before polling AHBIDLE.
This code can be found in Simplicity Studio > Application Notes > AN0065 EFM32 as USB Device > Import Project > STK3700_usb_device.slsproj(or different extension depending on your preferred IDE) > OK.
After this project opens in the Simplicity Studio IDE, the source code can be found in emusb\em_usbhal.c > USBHAL_CoreReset().
How can I obtain Material Declaration Data Sheet, RoHS, Lead (Pb) Free, PFOS, REACH, and Halogen Free documentation for Silicon Labs devices?
Answer
Environmental & Regulatory documents are made available through MDDS "Material Declaration Data Sheet" via the RFI Portal (free registration required). This portal provides the following documentation for many of our devices:
Detailed Device Composition (MDDS)
Halogen Free Certificate of Compliance
Material Test Results
Pb Free Confirmation
PFOS Certificate of Compliance
PFOS/PFOA Free Confirmation
REACH Declaration
RoHS Certificate of Compliance
To access this content, follow the initial instructions provided in the Knowledge Base article Qualification report up to step # 7. At that point, navigate to and "checkmark" one or more of the following options - captured as an example for an EFM32GG MCU:
After making your selections, click the red arrow to query the RFI Portal for your desired documentation and generate your search results:
32-bit Knowledge Base
Device power up sequence in self-powered USB mode
Layout and Soldering Information
Happy Gecko USB vs. Wonder Gecko, Giant Gecko, and Leopard Gecko
USB audio examples for EFM32
Device not recognized with an EFM32 kit
EFM32 USB CDC driver location
USB GRSTCTL AHBIDLE flag is never set
How to obtain Environmental & Regulatory documents for Silicon Labs devices
Solder composition for EFM32 products
通过USB MCU实现一个通过USB转UART的转换器有哪些方案?