In USB host applications, Nuvoton MCUs will not take the initiative to provide 5V voltage to Vbus. Additional 5V needs to be designed for system circuit to provide to USB devices required to be connected.

In NuTiny-SDK-M451 development board, for example, 5V is provided by the Nu-Link-Me ICE Debugger end USB. When the USB interface is switched as Host in M451, the use of USB_VBUS_EN OTG pin enables NCT3520U (Nuvoton high-side current-limited switches) to output 5V voltage to Vbus. When the USB interface is switched as Device in M451, OTG will disable the NCT3520U.

In addition, NCT3520U provides overcurrent detection. Once the USB_VBUS_ST OTG pin receives an overcurrent signal, the USB_VBUS_EN pin does not need to be set through software, and OTG hardware will take the initiative to set USB_VBUS_EN pin to prohibit 5V voltage output to protect the entire system.

In USB host applications, if the customer has no experiences in designing overcurrent protection and Vbus voltage control, but directly supplies 5V voltage to Vbus, the program needs to be modified, and the USB_VBUS_EN and USB_VBUS_ST pin need to be switched to general I/O.

Please refer to the design schematic of NuTiny-EVB-M451 development board:
http://www.nuvoton.com/opencms/resource-download.jsp?tp_GUID=HL0120141225192023

Products:	Microcontrollers ,Arm Cortex-M4 MCUs ,M452 USB Series ,M453 CAN Series ,NUC442/472 Series ,NUC505 Series
Applications:
Function:	Peripherals,Connectivity,USB

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How to do overcurrent protection and Vbus voltage control in USB host applications? Issue Date：2015-02-04

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