ESP32-S3 ADC2电压偏差是什么原因造成的？

1. 使用ESP32-S3 ADC2 CH7(GPIO18)，读取校准后的电压偏低。实际是2V左右，log打印只有1.8V多。没有打开wifi，请问可能是什么问题？

2. 另外如果直接计算adc_raw/4095*Vref，这个Vref是多少

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I (100531) bat_adc: adc_raw= 2238 cali_data= 1803mV
I (102531) bat_adc: adc_raw= 2238 cali_data= 1803mV
I (104531) bat_adc: adc_raw= 2236 cali_data= 1800mV
I (106531) bat_adc: adc_raw= 2236 cali_data= 1800mV
I (108531) bat_adc: adc_raw= 2238 cali_data= 1803mV
I (110531) bat_adc: adc_raw= 2237 cali_data= 1802mV
I (112531) bat_adc: adc_raw= 2237 cali_data= 1802mV
I (114531) bat_adc: adc_raw= 2237 cali_data= 1802mV
I (116531) bat_adc: adc_raw= 2237 cali_data= 1802mV
I (118531) bat_adc: adc_raw= 2237 cali_data= 1802mV
I (120531) bat_adc: adc_raw= 2235 cali_data= 1800mV
I (122531) bat_adc: adc_raw= 2239 cali_data= 1803mV


附上ADC2读取函数：
Code: Select all
//ADC Channels
#define ADC_EXAMPLE_CHAN0    ADC2_CHANNEL_7   // GPIO18

//ADC Attenuation
#define ADC_EXAMPLE_ATTEN    ADC_ATTEN_DB_11

//ADC Calibration
#if CONFIG_IDF_TARGET_ESP32
#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_VREF
#elif CONFIG_IDF_TARGET_ESP32S2
#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_TP
#elif CONFIG_IDF_TARGET_ESP32C3
#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_TP
#elif CONFIG_IDF_TARGET_ESP32S3
#define ADC_EXAMPLE_CALI_SCHEME ESP_ADC_CAL_VAL_EFUSE_TP_FIT
#endif

static esp_adc_cal_characteristics_t adc_chars;

static bool adc_calibration_init(void)
{
    esp_err_t ret;
    bool cali_enable = false;

    ret = esp_adc_cal_check_efuse(ADC_EXAMPLE_CALI_SCHEME);
    if (ret == ESP_ERR_NOT_SUPPORTED)
    {
        ESP_LOGW(TAG, "Calibration scheme not supported, skip software calibration");
    }
    else if (ret == ESP_ERR_INVALID_VERSION)
    {
        ESP_LOGW(TAG, "eFuse not burnt, skip software calibration");
    }
    else if (ret == ESP_OK)
    {
        cali_enable = true;
        esp_adc_cal_characterize(ADC_UNIT_2, ADC_EXAMPLE_ATTEN, ADC_WIDTH_BIT_DEFAULT, 0, &adc_chars);
    }
    else
    {
        ESP_LOGE(TAG, "Invalid arg");
    }

    return cali_enable;
}

esp_err_t adc_init(void)
{
    bool cali_enable = adc_calibration_init();
    if (true != cali_enable)
    {
        ESP_LOGI(TAG, "adc init fail!!!");
        return ESP_FAIL;
    }
   
    //ADC2 config
    ESP_ERROR_CHECK(adc2_config_channel_atten(ADC_EXAMPLE_CHAN0, ADC_EXAMPLE_ATTEN));

    ESP_LOGI(TAG, "adc init ok");
    return ESP_OK;
}

uint16_t adc_get_voltage(void)
{
    uint16_t adc_raw;
    uint16_t voltage = 0;

    adc2_get_raw(ADC_EXAMPLE_CHAN0, ADC_WIDTH_BIT_DEFAULT, &adc_raw);
    voltage = esp_adc_cal_raw_to_voltage(adc_raw, &adc_chars);

    ESP_LOGI(TAG, "adc_raw= %d cali_data= %dmV", adc_raw, voltage);

    return voltage;
}