STM32F401 USB VBUS 设置引起的一些问题

在开发板上调试代码，开发板上的PA9是floating input 。 然后贴片的时候我们的板子应用了这个引脚并且设置为GPIO_MODE_OUTPUT_PP。

最后引起的问题是USB不能正常通信。

最后查看手册看到如下描述：

Note: When VBUS sensing feature is enabled, PA9 should be left at their default state (floating

input), not as alternate function. A typical 200 μA current consumption of the embedded

sensing block (current to voltage conversion to determine the different sessions) can be

observed on PA9 when the feature is enabled.

最后不得不修改代码如下：

USBD_StatusTypeDef  USBD_LL_Init (USBD_HandleTypeDef *pdev)

{ 

  /* Init USB_IP */

  if (pdev->id == DEVICE_FS) {

  /* Link The driver to the stack */    

  hpcd_USB_OTG_FS.pData = pdev;

  pdev->pData = &hpcd_USB_OTG_FS; 

  hpcd_USB_OTG_FS.Instance = USB_OTG_FS;

  hpcd_USB_OTG_FS.Init.dev_endpoints = 4;

  hpcd_USB_OTG_FS.Init.speed = PCD_SPEED_FULL;

  hpcd_USB_OTG_FS.Init.dma_enable = DISABLE;

  hpcd_USB_OTG_FS.Init.ep0_mps = DEP0CTL_MPS_64;

  hpcd_USB_OTG_FS.Init.phy_itface = PCD_PHY_EMBEDDED;

  hpcd_USB_OTG_FS.Init.Sof_enable = DISABLE;

  hpcd_USB_OTG_FS.Init.low_power_enable = DISABLE;

  hpcd_USB_OTG_FS.Init.lpm_enable = DISABLE;

  //hpcd_USB_OTG_FS.Init.vbus_sensing_enable = ENABLE;

  hpcd_USB_OTG_FS.Init.use_dedicated_ep1 = DISABLE;

  if (HAL_PCD_Init(&hpcd_USB_OTG_FS) != HAL_OK)

  {

    Error_Handler();

  }

  HAL_PCDEx_SetRxFiFo(&hpcd_USB_OTG_FS, 0x80);

  HAL_PCDEx_SetTxFiFo(&hpcd_USB_OTG_FS, 0, 0x40);

  HAL_PCDEx_SetTxFiFo(&hpcd_USB_OTG_FS, 1, 0x80);

  }

  return USBD_OK;

}

屏蔽标红部分，USB就能够正常通信。