Stm32f103 DAC 最低电流输出问题

void AnalogInit(void)

{

    DAC_InitTypeDef  DAC_InitStructure;

    GPIO_InitTypeDef GPIO_InitStructure;



      RCC_APB2PeriphClockCmd(RCC_APB2Periph_AFIO | RCC_APB2Periph_GPIOA, ENABLE);

      /* DAC Periph clock enable */

      RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);

      

    /* Configure DAC channe1 output pin */

    GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_4;

    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;

    GPIO_Init(GPIOA, &GPIO_InitStructure);



    /* Configure DAC channe1 output pin */

    GPIO_InitStructure.GPIO_Pin =  GPIO_Pin_5;

    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;

    GPIO_Init(GPIOA, &GPIO_InitStructure);



    

    /* DAC channel1 Configuration */

    DAC_InitStructure.DAC_Trigger = DAC_Trigger_Software;

    DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;

    DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Disable;    //输出缓冲失能    

    DAC_InitStructure.DAC_LFSRUnmask_TriangleAmplitude = DAC_TriangleAmplitude_4095;



    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);



}



//端口1AD值更新

void DAC1_update(u16 ch1)

{

    ch1 = (ch1 <<4) & 0xfff0;

    /* Set DAC Channel1 DHR12L register */

    DAC_SetChannel1Data(DAC_Align_12b_L, ch1);



    /* Start DAC Channel1 conversion by software */

    DAC_SoftwareTriggerCmd(DAC_Channel_1, ENABLE);

}



void DAC2_update(u16 ch2)

{

    ch2 = (ch2 <<4) & 0xfff0;

    /* Set DAC Channel2 DHR12L register */

    DAC_SetChannel2Data(DAC_Align_12b_L, ch2);



    /* Start DAC Channel1 conversion by software */

    DAC_SoftwareTriggerCmd(DAC_Channel_2, ENABLE);

}