STM32F405 ADC内部上拉的问题求解

我正在使用带有 DMA（循环）的三重同时转换 ADC（每个 2 次转换）：

static void MX_ADC1_Init(void)
{
ADC_MultiModeTypeDef multimode = {0};
ADC_ChannelConfTypeDef sConfig = {0};
/** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
*/
hadc1.Instance = ADC1;
hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;
hadc1.Init.Resolution = ADC_RESOLUTION_12B;
hadc1.Init.ScanConvMode = ENABLE;
hadc1.Init.ContinuousConvMode = DISABLE;
hadc1.Init.DiscontinuousConvMode = DISABLE;
hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_RISING;
hadc1.Init.ExternalTrigConv = ADC_EXTERNALTRIGCONV_T8_TRGO;
hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc1.Init.NbrOfConversion = 2;
hadc1.Init.DMAContinuousRequests = ENABLE;
hadc1.Init.EOCSelection = ADC_EOC_SEQ_CONV;
if (HAL_ADC_Init(&hadc1) != HAL_OK)
{
Error_Handler();
}
/** Configure the ADC multi-mode
*/
multimode.Mode = ADC_TRIPLEMODE_REGSIMULT;
multimode.DMAAccessMode = ADC_DMAACCESSMODE_1;
multimode.TwoSamplingDelay = ADC_TWOSAMPLINGDELAY_5CYCLES;
if (HAL_ADCEx_MultiModeConfigChannel(&hadc1, &multimode) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_12;
sConfig.Rank = 1;
sConfig.SamplingTime = ADC_SAMPLETIME_28CYCLES;
if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_7;
sConfig.Rank = 2;
if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief ADC2 Initialization Function
* @param None
* @retval None
*/
static void MX_ADC2_Init(void)
{
ADC_ChannelConfTypeDef sConfig = {0};
/** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
*/
hadc2.Instance = ADC2;
hadc2.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;
hadc2.Init.Resolution = ADC_RESOLUTION_12B;
hadc2.Init.ScanConvMode = ENABLE;
hadc2.Init.ContinuousConvMode = DISABLE;
hadc2.Init.DiscontinuousConvMode = DISABLE;
hadc2.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc2.Init.NbrOfConversion = 2;
hadc2.Init.DMAContinuousRequests = DISABLE;
hadc2.Init.EOCSelection = ADC_EOC_SEQ_CONV;
if (HAL_ADC_Init(&hadc2) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_11;
sConfig.Rank = 1;
sConfig.SamplingTime = ADC_SAMPLETIME_28CYCLES;
if (HAL_ADC_ConfigChannel(&hadc2, &sConfig) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_14;
sConfig.Rank = 2;
if (HAL_ADC_ConfigChannel(&hadc2, &sConfig) != HAL_OK)
{
Error_Handler();
}
}
/**
* @brief ADC3 Initialization Function
* @param None
* @retval None
*/
static void MX_ADC3_Init(void)
{
ADC_ChannelConfTypeDef sConfig = {0};
/** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
*/
hadc3.Instance = ADC3;
hadc3.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;
hadc3.Init.Resolution = ADC_RESOLUTION_12B;
hadc3.Init.ScanConvMode = ENABLE;
hadc3.Init.ContinuousConvMode = DISABLE;
hadc3.Init.DiscontinuousConvMode = DISABLE;
hadc3.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc3.Init.NbrOfConversion = 2;
hadc3.Init.DMAContinuousRequests = DISABLE;
hadc3.Init.EOCSelection = ADC_EOC_SEQ_CONV;
if (HAL_ADC_Init(&hadc3) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_10;
sConfig.Rank = 1;
sConfig.SamplingTime = ADC_SAMPLETIME_28CYCLES;
if (HAL_ADC_ConfigChannel(&hadc3, &sConfig) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_13;
sConfig.Rank = 2;
if (HAL_ADC_ConfigChannel(&hadc3, &sConfig) != HAL_OK)
{
Error_Handler();
}
}

我的问题是 ADC3 (PC3) 的通道 13 - 它正在测量一个简单的分压器：

即使在移除 R2 和 C2 之后，万用表和 ADC 都显示在 3.2V 左右（似乎内部上拉）。例如，当我将引脚模式更改为 AF_OD 或 OUTPUT_OD 时，电压为 0.6-0.8V。但是，如果我切换回模拟，无论如何电压都会升至 3.2。我在 C2 的位置焊接了 6k8 电阻以产生更强的下拉，但这并没有改变任何事情......
关于可能是什么问题的任何想法？