Hi there,
I have a custom board with an STM32F070. The VDD and VDDA are connected together. System runs at 48 MHz from a 8 MHz crystal. Each VDD has a 100nF cap. VDD is 3.3V, from a 1% LDO.
The code uses UART1, UART2, USB and I2C2. Also, many I/O pins. All works correctly.
I have a single channel (ADC_IN5) conversion, with a simple polling. Result of conversion fluctuates by several hundreds even at 0V (ie. from 0 up to 300).
The initialitation code is below:
/**
* @brief ADC Initialization Function
* @PAram None
* @retval None
*/
static void MX_ADC_Init(void)
{
/* USER CODE BEGIN ADC_Init 0 */
/* USER CODE END ADC_Init 0 */
ADC_ChannelConfTypeDef sConfig = {0};
/* USER CODE BEGIN ADC_Init 1 */
/* USER CODE END ADC_Init 1 */
/** Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
*/
hadc.Instance = ADC1;
hadc.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV1;
hadc.Init.Resolution = ADC_RESOLUTION_12B;
hadc.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc.Init.ScanConvMode = ADC_SCAN_DIRECTION_FORWARD;
hadc.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
hadc.Init.LowPowerAutoWait = DISABLE;
hadc.Init.LowPowerAutoPowerOff = DISABLE;
hadc.Init.ContinuousConvMode = DISABLE;
hadc.Init.DiscontinuousConvMode = DISABLE;
hadc.Init.ExternalTrigConv = ADC_SOFTWARE_START;
hadc.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
hadc.Init.DMAContinuousRequests = DISABLE;
hadc.Init.Overrun = ADC_OVR_DATA_PRESERVED;
if (HAL_ADC_Init(&hadc) != HAL_OK)
{
Error_Handler();
}
/** Configure for the selected ADC regular channel to be converted.
*/
sConfig.Channel = ADC_CHANNEL_5;
sConfig.Rank = ADC_RANK_CHANNEL_NUMBER;
sConfig.SamplingTime = ADC_SAMPLETIME_1CYCLE_5;
if (HAL_ADC_ConfigChannel(&hadc, &sConfig) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN ADC_Init 2 */
// ADC Initialization
HAL_ADCEx_Calibration_Start(&hadc);
/* USER CODE END ADC_Init 2 */
}
The polling code is below:
// Perform ADC conversion
HAL_ADC_Start(&hadc); // Enables ADC and starts conversion
// Waits for a conversion to be performed with a 10 ms timeout
if(HAL_ADC_PollForConversion(&hadc,10) == HAL_OK)
{
value = HAL_ADC_GetValue(&hadc);
}
HAL_ADC_Stop(&hadc); // Stops conversion
And the config:
What am I missing? Thank you!
Thanks for replying, but the sampling time is not the issue. I believe there is a fundamental problem.
I have increased the sampling time to maximum anyway.
The ADC pin is going HIGH during conversion. Below is the waveform at 239.5 cycles, which match the timing on the scope considering ADC running at 14MHz.
This pull-up is periodic, of course, I am doing ADC polling at around 20ms.
But the pulling-up level is also consistent: if I put an external pull-down, the peak voltage on the pin consistently gets reduced reducing the pull-down resistance. On this case the resistor is 820R.
So, my conclusion is that there is something pulling up the pin when the conversion is started.
