In adc.h file there is such notes ;
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The default ADC full-scale voltage is 1.1V. To read higher voltages (up to the pin maximum voltage,
* usually 3.3V) requires setting >0dB signal attenuation for that ADC channel.
* When VDD_A is 3.3V:
* - 0dB attenuaton (ADC_ATTEN_DB_0) gives full-scale voltage 1.1V
* - 2.5dB attenuation (ADC_ATTEN_DB_2_5) gives full-scale voltage 1.5V
* - 6dB attenuation (ADC_ATTEN_DB_6) gives full-scale voltage 2.2V
* - 11dB attenuation (ADC_ATTEN_DB_11) gives full-scale voltage 3.9V (see note below)
* @note The full-scale voltage is the voltage corresponding to a maximum reading (depending on ADC1 configured
* bit width, this value is: 4095 for 12-bits, 2047 for 11-bits, 1023 for 10-bits, 511 for 9 bits.)
* @note At 11dB attenuation the maximum voltage is limited by VDD_A, not the full scale voltage.
* Due to ADC characteristics, most accurate results are obtained within the following approximate voltage ranges:
* - 0dB attenuaton (ADC_ATTEN_DB_0) between 100 and 950mV
* - 2.5dB attenuation (ADC_ATTEN_DB_2_5) between 100 and 1250mV
* - 6dB attenuation (ADC_ATTEN_DB_6) between 150 to 1750mV
* - 11dB attenuation (ADC_ATTEN_DB_11) between 150 to 2450mV
* For maximum accuracy, use the ADC calibration APIs and measure voltages within these recommended ranges.
So what is attenuation ? i can not see any attenuation in datasheet if i am not wrong. There is pga unit in datasheet so attenuation 0 means maximum pga gain ? is there any relation these attenuation and pga ?if yes why did you do such confusion , if no what is this attenuation and where pga defined in adc.h file for configuration?