STM32F030 ADC采样问题

L342785896 提问时间：2016-5-23 12:02 /

大家好：
我的ADC初始化如下：
void  Adc_Init(void)
{
      ADC_InitTypeDef ADC_InitStructure;
      GPIO_InitTypeDef GPIO_InitStructure;

      RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1       , ENABLE );       //Ê¹ÄÜADC1Í¨µÀÊ±ÖÓ
      RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA       , ENABLE );       //Ê¹ÄÜHGPIOAÍ¨µÀÊ±ÖÓ

      RCC_ADCCLKConfig(RCC_ADCCLK_PCLK_Div4); //ÉèÖÃADC·ÖÆµÒò×Ó4 48M/4=12,ADC×î´óÊ±¼ä²»ÄÜ³¬¹ý14M

      //PA5 ×÷ÎªÄ£ÄâÍ¨µÀÊäÈëÒý½Å
      GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;
      GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;             //Ä£ÄâÊäÈëÒý½Å
      GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;
      GPIO_Init(GPIOA, &GPIO_InitStructure);

      ADC_DeInit(ADC1);  //¸´Î»ADC1,½«ÍâÉè ADC1 µÄÈ«²¿¼Ä´æÆ÷ÖØÉèÎªÈ±Ê¡Öµ
      ADC_StructInit(&ADC_InitStructure);

  /* Configure the ADC1 in continous mode withe a resolutuion equal to 12 bits  */
  ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;
  ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;
  ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;
  ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
  ADC_InitStructure.ADC_ScanDirection = ADC_ScanDirection_Upward;
  ADC_Init(ADC1, &ADC_InitStructure);

//       ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b; //×ª»»¾«¶È
//       ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;       //µ¥´Î×ª»»Ä£Ê½
//       ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None; //×ª»»ÓÉÈí¼þ¶ø²»ÊÇÍâ²¿´¥·¢Æô¶¯
//       ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right; //Êý¾ÝÓÒ¶ÔÆë
//       ADC_InitStructure.ADC_ScanDirection = ADC_ScanDirection_Upward;
//       ADC_Init(ADC1, &ADC_InitStructure);

      ADC_ChannelConfig(ADC1, ADC_Channel_5 , ADC_SampleTime_71_5Cycles);

      ADC_GetCalibrationFactor(ADC1);//ADCÐ£×¼
      ADC_Cmd(ADC1, ENABLE);       //Ê¹ÄÜÖ¸¶¨µÄADC1

  /* µÈ´ýADRDY falg */
  while(!ADC_GetFlagStatus(ADC1, ADC_FLAG_ADRDY));

  /* ADC1 regular Software Start Conv */
  ADC_StartOfConversion(ADC1);       //¿ªÆôÈí¼þ×ª»»

}

现在运行后发现，ADC脚输出3.7V电压，不知道为什么？