Voltage with DACs unstable

[FTrom]

I'm using the DACs of STM32F303K8.

The max voltage of the DAC1 is 3.3V but the second is 3V.

I don't find any explanation for it and it looks like also quite strange.

PS. To my nucleo is not. Connected to any Vref. It is necessary?

Anyone can help me?

[Peter BENSCH]

What is your DAC configuration (with/without buffer), what load is connected to the DACs?

Regards

/Peter

[FTrom]

Hi Peter

In the file .ioc the DAC2 (connected to PA6 ) is OUT1 Configuration "DAC Output switch Enable".

In the DAC1 (connected to PA4) the OUT2 Configuration is Disable.

Following the initialization in the program:

static void MX_DAC1_Init(void)
 
{
 
 
 
 /* USER CODE BEGIN DAC1_Init 0 */
 
 
 
 /* USER CODE END DAC1_Init 0 */
 
 
 
 DAC_ChannelConfTypeDef sConfig = {0};
 
 
 
 /* USER CODE BEGIN DAC1_Init 1 */
 
 
 
 /* USER CODE END DAC1_Init 1 */
 
 /** DAC Initialization
 
 */
 
 hdac1.Instance = DAC1;
 
 if (HAL_DAC_Init(&hdac1) != HAL_OK)
 
 {
 
  Error_Handler();
 
 }
 
 /** DAC channel OUT1 config
 
 */
 
 sConfig.DAC_Trigger = DAC_TRIGGER_NONE;
 
 sConfig.DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE;
 
 if (HAL_DAC_ConfigChannel(&hdac1, &sConfig, DAC_CHANNEL_1) != HAL_OK)
 
 {
 
  Error_Handler();
 
 }
 
 /* USER CODE BEGIN DAC1_Init 2 */
 
 
 
 /* USER CODE END DAC1_Init 2 */
 
 
 
}

static void MX_DAC2_Init(void)
{
 
  /* USER CODE BEGIN DAC2_Init 0 */
 
  /* USER CODE END DAC2_Init 0 */
 
  DAC_ChannelConfTypeDef sConfig = {0};
 
  /* USER CODE BEGIN DAC2_Init 1 */
 
  /* USER CODE END DAC2_Init 1 */
  /** DAC Initialization
  */
  hdac2.Instance = DAC2;
  if (HAL_DAC_Init(&hdac2) != HAL_OK)
  {
    Error_Handler();
  }
  /** DAC channel OUT1 config
  */
  sConfig.DAC_Trigger = DAC_TRIGGER_NONE;
  sConfig.DAC_OutputSwitch = DAC_OUTPUTSWITCH_ENABLE;
  if (HAL_DAC_ConfigChannel(&hdac2, &sConfig, DAC_CHANNEL_1) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN DAC2_Init 2 */
 
  /* USER CODE END DAC2_Init 2 */
 
}

[Peter BENSCH]

So the configuration looks identical.

What about my 2nd question: what load is connected to the DACs?

Regards

/Peter

[FTrom]

it is a high impedance of the ADC input of a Motor Driver. Each DAC drives with an analog signal the motor drivers. But the motor driver are identical.

PS I don't use any Vref so far.

[Peter BENSCH]

Hmm, I missed something: DAC1_OUT1 is buffered and DAC2_OUT1 is unbuffered, which in connection with the following load could explain the voltage drop. How many systems does the problem occur on?

Regards

/Peter

[FTrom]

Hi Peter,

"DAC1_OUT1 is buffered and DAC2_OUT1 is unbuffered": maybe but usually there is a voltage drop either when there is a low resistance or the power supply is not enough, which is not my case because I use an external power supply of 5V and circa 1 A.

sorry but I don't get your question: "How many systems does the problem occur on?"

What do you mean for system?

Thanks in advance

Fausto

[S.Ma]

Cut the dac outputs and measure. In debug mode, manually inspect the Dac registers too. Then continue digging.

[FTrom]

I did some deep measures and are not nice:

without any External Power supply of 5V but only the USB and the DACs without any load.

DAC1 is good: at 0 digits the voltage I measure 0 V, at 4095 digits I measure 3.287 V.

DAC2 not good: at 0 digits the voltage I measure 0.1 V, at 4095 digits I measure 3.6 V.

with External Power supply supply of 5V and the DACs without any load

DAC1 is good: at 0 digits the voltage I measure 0 V, at 4095 digits I measure 3.288 V.

DAC2 not good: at 0 digits the voltage I measure 0.610 V, at 4095 digits I measure 3.6 V.

Maybe I forgot to say: I'm using a Nucleo STM32F303K8

Thanks

Fausto

[waclawek.jan]

Have you disconnected all onboard connections to the DAC pin (maybe SB16)?

JW