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.
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?
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)?
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.
How can I obtain Material Declaration Data Sheet, RoHS, Lead (Pb) Free, PFOS, REACH, and Halogen Free documentation for Silicon Labs devices?
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
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: