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Noisy DAC on STM32F303

Question asked by Palaima.Emmett on Aug 8, 2016
Latest reply on Aug 16, 2016 by FTITI.Walid
Hi, I just set up DAC output on the STM32F303 Discovery Board and I'm noticing a lot of wideband noise on the output (about .5 volts peak to peak), even when I set it to a constant value within my program. Is there something in the way I'm am setting up DAC output that might be causing this? I based the output configuration off of the DMA_RAM_DAC peripheral example project.

Here is my code for setting up DAC output, please let me know if you see anything: 

int main(void)
{
  /*!< At this stage the microcontroller clock setting is already configured, 
       this is done through SystemInit() function which is called from startup
       file (startup_stm32f30x.s) before to branch to application main.
       To reconfigure the default setting of SystemInit() function, refer to
       system_stm32f30x.c file
     */
  

  DMA_Config();
  DAC_Config();
  TIM_Config();

  while (1)
  {
       DAC1Output = 4095;
  }
}


/**
  * @brief  Configures the TIM2
  * @param  None
  * @retval None
  */
static void TIM_Config(void)
{
  TIM_TimeBaseInitTypeDef    TIM_TimeBaseStructure;


  /* TIM2 Periph clock enable */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);


  /* Time base configuration */
  TIM_TimeBaseStructInit(&TIM_TimeBaseStructure); 
  TIM_TimeBaseStructure.TIM_Period = 0xFF;//0xFF;
  TIM_TimeBaseStructure.TIM_Prescaler = 0x0;       
  TIM_TimeBaseStructure.TIM_ClockDivision = 0x0;    
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  
  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);


  /* TIM2 TRGO selection: update event is selected as trigger for DAC */
  TIM_SelectOutputTrigger(TIM2, TIM_TRGOSource_Update);


  /* TIM2 enable counter */
  TIM_Cmd(TIM2, ENABLE);
}


/**
  * @brief  Configures DAC channel 1 and channel 2
  * @param  None
  * @retval None
  */
static void DAC_Config(void)
{
  DAC_InitTypeDef   DAC_InitStructure;
  GPIO_InitTypeDef  GPIO_InitStructure;
  
  /* Enable GPIOA Periph clock --------------------------------------*/
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
  
  /* Configure PA.04 (DAC1_OUT1), PA.05 (DAC1_OUT2) as analog */
  GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_4 | GPIO_Pin_5;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOA, &GPIO_InitStructure);
  
  /* DAC Periph clock enable */
  RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);
  
  /* Fill DAC InitStructure */
  DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;
  DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;
  //DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_4095;
  DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable;
  
  /* DAC channel1 Configuration */
  DAC_Init(DAC_Channel_1, &DAC_InitStructure);
  
  /* DAC channel2 Configuration */
  DAC_Init(DAC_Channel_2, &DAC_InitStructure);
  
  /* Enable DAC Channel1: Once the DAC channel1 is enabled, PA.04 is 
  automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_1, ENABLE);
  
  /* Enable DAC Channel2: Once the DAC channel2 is enabled, PA.05 is 
  automatically connected to the DAC converter. */
  DAC_Cmd(DAC_Channel_2, ENABLE);
  
  /* Enable DMA for DAC Channel1 */
  DAC_DMACmd(DAC_Channel_1, ENABLE);
}


/**
  * @brief  Configures DMA2 channel3
  * @param  None
  * @retval None
  */
static void DMA_Config(void)
{
  DMA_InitTypeDef   DMA_InitStructure;


  /* Enable DMA2 clock -------------------------------------------------------*/
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA2, ENABLE);


  DMA_DeInit(DMA2_Channel3);
  DMA_InitStructure.DMA_PeripheralBaseAddr = DAC_DHR12RD_Address;
  DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)&DAC1Output;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;
  DMA_InitStructure.DMA_BufferSize = 1;
  DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Disable;
  DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
  DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
  DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
  DMA_InitStructure.DMA_Priority = DMA_Priority_High;
  DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
  DMA_Init(DMA2_Channel3, &DMA_InitStructure);


  /* Enable DMA2 Channel3 */
  DMA_Cmd(DMA2_Channel3, ENABLE);
}

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