Point of ADC saturation really depends on your reference voltage and your chosen prescaling. If you use the 1.2V VBG internal reference voltage the ADC range will be 0-1.2V with a saturation of 1.2V. This means that your AIN signal with 1/1 prescaling should be in the range 0-1.2V in order to obtain proper conversion. Input above 1.2V will just be converted to the maximum ADC value. However if you use for example 1/3 prescaling for your AIN input the input is scaled down by 1/3. The effect is that your AIN voltage range is 0-3.6V, because the 3.6V input voltage is scaled down to 3.6/3=1.2V.
Examples of saturation points for ADC AIN inputs are:
1.2VBG reference, AIN 1/1 prescaling: AIN 1.2V
1.2VBG reference, AIN 2/3 prescaling: AIN 1.8V
1.2VBG reference, AIN 1/3 prescaling: AIN 3.6V
1.0V AREF, AIN 1/1 prescaling: AIN 1.0V
1.0V AREF, AIN 2/3 prescaling: AIN 1.5V
1.0V AREF, AIN 1/3 prescaling: AIN 3.0V
VDD is 3.0V, VDD 1/2 reference, AIN 1/1 prescaling: AIN 1.5V
Point of ADC saturation really depends on your reference voltage and your chosen prescaling. If you use the 1.2V VBG internal reference voltage the ADC range will be 0-1.2V with a saturation of 1.2V. This means that your AIN signal with 1/1 prescaling should be in the range 0-1.2V in order to obtain proper conversion. Input above 1.2V will just be converted to the maximum ADC value. However if you use for example 1/3 prescaling for your AIN input the input is scaled down by 1/3. The effect is that your AIN voltage range is 0-3.6V, because the 3.6V input voltage is scaled down to 3.6/3=1.2V.
Examples of saturation points for ADC AIN inputs are:
1.2VBG reference, AIN 1/1 prescaling: AIN 1.2V
1.2VBG reference, AIN 2/3 prescaling: AIN 1.8V
1.2VBG reference, AIN 1/3 prescaling: AIN 3.6V
1.0V AREF, AIN 1/1 prescaling: AIN 1.0V
1.0V AREF, AIN 2/3 prescaling: AIN 1.5V
1.0V AREF, AIN 1/3 prescaling: AIN 3.0V
VDD is 3.0V, VDD 1/2 reference, AIN 1/1 prescaling: AIN 1.5V
According to the nRF51882 Product Specification, the input voltage on any IO Pin must not exceed VDD + 0.3V.
This means that ADC inputs must not exceed 2.1V if the nRF51822 is supplied by 1.8V, is this correct? I guess this is also true even if the ADC input is prescaled with 1/3 or 2/3 right?
