What is the maximum input voltage for the ADC

[Anonymous]

What is the maximum input voltage on ADC analog input pins?

[Stefan Birnir Sverrisson]

There are basically two rules to follow when deciding max voltage on ADC analog input (AIN) pins:

1. The ADC should not be exposed to higher voltage than 2.4V on an ADC AIN pin after prescaling
2. GPIO pin should not be exposed to higher voltage than VDD+0.3V, see Aboslute maximum ratings in the nRF51822/nRF51422 Product Specification

For example, when having 2/3 prescaling you can expose 2.4V/(2/3)=3.6V to an AIN pin. For not to violate rule 2, VDD should be 3.3V or higher in this case.

These are the maximum voltages that can be exposed to an ADC AIN pins in order for not to damage the ADC, depending on supply voltage and your prescale settings:

VDD 3.6, prescaling 1/1: AIN max 2.4V  (rule 1 limitation)  
VDD 3.6, prescaling 2/3: AIN max 3.6V  (rule 1 limitation)  
VDD 3.6, prescaling 1/3: AIN max 3.9V  (rule 2 limitation)  
VDD 3.3, prescaling 1/1: AIN max 2.4V  (rule 1 limitation)  
VDD 3.3, prescaling 2/3: AIN max 3.6V  (rule 1 and rule 2 limitation)  
VDD 3.3, prescaling 1/3: AIN max 3.6V  (rule 2 limitation)  
VDD 1.8, prescaling 1/1: AIN max 2.1V  (rule 2 limitation)  
VDD 1.8, prescaling 2/3: AIN max 2.1V  (rule 2 limitation)  
VDD 1.8, prescaling 1/3: AIN max 2.1V  (rule 2 limitation)