How should the EOT_N be connected to accomplish a vbus sensing functionality?
In a self-powered system, when the USB connection has been removed, there may not be any indication to the microcontroller that the USB cable is disconnected. To detect a disconnection, the EOT_N pin has dual functionality; that is, to function as an EOT (end of transfer) during DMA mode and to detect VBUS sensing (The vbus is the 5V power supply pin from the USB connector). For VBUS sensing, the EOT_N is connected to the vbus via a 1 kW resistor and a 1 MW bleeding resistor is required to leak the charges to ensure that EOT_N goes to zero when vbus is removed. So, when the device is in self-power mode and when the Host is OFF, even if the USB cable is connected, the device will check the non-availability of VBUS (through the EOT_N pin) and switch off the internal SOFTCONNECT resistor. This ensures that the device PDIUSBD12 is disconnected and does not power the D+ line unnecessarily.
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